Dark Matter Doesn't Exist(iai.tv)
iai.tv
Dark Matter Doesn't Exist
https://iai.tv/articles/dark-matter-doesnt-exist-auid-2180
398 comments
> * The current best theory of the structure formation and galaxy evolution involves dark matter and critically depend on it to reproduce observations.
Dark matter models are fine-tuned to reproduce certain observations. These don't really count as evidence in favour of DM.
> * It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.
MOND has more points in favour for it as a preferred theory than DM models. See [1].
> Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.
I'm not sure why I should find your claim that DM is "essential" as persuasive given MOND has received orders of magnitude less attention and less development than DM models. I would certainly not bet any money on MOND being incapable of reproducing these observations.
[1] From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
Dark matter models are fine-tuned to reproduce certain observations. These don't really count as evidence in favour of DM.
> * It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.
MOND has more points in favour for it as a preferred theory than DM models. See [1].
> Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.
I'm not sure why I should find your claim that DM is "essential" as persuasive given MOND has received orders of magnitude less attention and less development than DM models. I would certainly not bet any money on MOND being incapable of reproducing these observations.
[1] From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
> Dark matter models are fine-tuned to reproduce certain observations
That's the definition of physics. Models are fine-tuned to match the observation and be predictive.
That's the definition of physics. Models are fine-tuned to match the observation and be predictive.
> That's the definition of physics. Models are fine-tuned to match the observation and be predictive.
That's not what "fine-tuned" means. Epicycles can be fine-tuned to reproduce the motion we see from elliptical orbits. However, we should clearly prefer the theory of elliptical orbits because it reproduces observations without any extra parameters needed to fine-tune it.
That's not what "fine-tuned" means. Epicycles can be fine-tuned to reproduce the motion we see from elliptical orbits. However, we should clearly prefer the theory of elliptical orbits because it reproduces observations without any extra parameters needed to fine-tune it.
In physics, a (free) parameter is finely-tuned when the model is highly sensitive to different values at high precisions. If you get radically different results for some parameter k = 0.0000000010 and k = 0.0000000011, and observations match only the first case but clearly do not match the second (or any value much larger or smaller than either of these), then the value of parameter k is finely-tuned.
One may need to add more free parameters to a theory, but those parameters need not be finely tuned.
A free parameter is one that must be measured or estimated, as opposed to dependent parameters which are fixed by the theory (and possibly its free parameters).
The pointwise energy-density of dark matter, or its contribution to the stress-energy tensor at a point -- a free parameter -- is presently only estimated, but that estimate is not finely-tuned. In fact, that's part of the practical problem of proving particle dark matter: the pointwise density is underdetermined by observation. As a result, we don't know whether the DM particles must all have very small masses, or whether there can be a mix of masses right up to masses comparable to that of Jupiter. We also don't know the density-gradient very precisely within galaxy clusters and individual galaxies. However, we get coarsely-similar galaxies and clusters in simulations for a wide variety of choices in these areas. So therefore, the dark-matter density (and its gradient, if any) are not finely-tuned. We must therefore search the parameter space to exclude many families of possibilities as significant contributors to dark matter energy-density. (Which has happened: many types of MACHO have been ruled out by observation; various supersymmetry candidates for WIMPs have been ruled out by experiment; most "warm" dark matter has been ruled out; and so forth).
If only the distribution of dark matter was finely-tuned, we could quickly narrow down the search space : <https://en.wikipedia.org/wiki/Dark_matter#Composition> (the last box in the table is for the cases where one has the mathematical freedom to choose to move some or all of the non-metric-tensor additional field(s) from the curvature side of the Einstein Field Equations to the matter side (where the stress-energy tensor is found), without prejudice as to whether it is more naturally (in a conceptual sense) a function on the curvature (which is why the cosmological constant appears on that side, where it could just as easily be written down as a function on stress-energy)).
One may need to add more free parameters to a theory, but those parameters need not be finely tuned.
A free parameter is one that must be measured or estimated, as opposed to dependent parameters which are fixed by the theory (and possibly its free parameters).
The pointwise energy-density of dark matter, or its contribution to the stress-energy tensor at a point -- a free parameter -- is presently only estimated, but that estimate is not finely-tuned. In fact, that's part of the practical problem of proving particle dark matter: the pointwise density is underdetermined by observation. As a result, we don't know whether the DM particles must all have very small masses, or whether there can be a mix of masses right up to masses comparable to that of Jupiter. We also don't know the density-gradient very precisely within galaxy clusters and individual galaxies. However, we get coarsely-similar galaxies and clusters in simulations for a wide variety of choices in these areas. So therefore, the dark-matter density (and its gradient, if any) are not finely-tuned. We must therefore search the parameter space to exclude many families of possibilities as significant contributors to dark matter energy-density. (Which has happened: many types of MACHO have been ruled out by observation; various supersymmetry candidates for WIMPs have been ruled out by experiment; most "warm" dark matter has been ruled out; and so forth).
If only the distribution of dark matter was finely-tuned, we could quickly narrow down the search space : <https://en.wikipedia.org/wiki/Dark_matter#Composition> (the last box in the table is for the cases where one has the mathematical freedom to choose to move some or all of the non-metric-tensor additional field(s) from the curvature side of the Einstein Field Equations to the matter side (where the stress-energy tensor is found), without prejudice as to whether it is more naturally (in a conceptual sense) a function on the curvature (which is why the cosmological constant appears on that side, where it could just as easily be written down as a function on stress-energy)).
> One may need to add more free parameters to a theory, but those parameters need not be finely tuned.
You're right I've been too loose with how I've been using the term "fine-tuning". Adding a parameter is not fine-tuning so much as just tuning.
The point I was trying to make is that both adding parameters to a theory to fit observations that it didn't predict, and fine-tuning it's parameters to fit should count against its plausibility, since they're both forms of tweaking the theory to match observations after the fact rather than making accurate predictions that follow naturally from the model being proposed.
You're right I've been too loose with how I've been using the term "fine-tuning". Adding a parameter is not fine-tuning so much as just tuning.
The point I was trying to make is that both adding parameters to a theory to fit observations that it didn't predict, and fine-tuning it's parameters to fit should count against its plausibility, since they're both forms of tweaking the theory to match observations after the fact rather than making accurate predictions that follow naturally from the model being proposed.
Famaey & McGaugh's review <https://arxiv.org/abs/1112.3960> (Stacey McGaugh is <https://tritonstation.com/>, a frequent critic of particle dark matter) §7 is all about adding whole new fields ("parameters") to standard General Relativity in order to capture higher-order terms in post-Newtonian expansions (in 1/c^n or in the metric tensor) of theories that preserve the central characteristics of Milgrom's MOND.
Those characteristics are: no "non-luminous" or "hidden" matter sources -- the glowing, refracting, and obscuring dusts are the sole sources of gravitation -- and in circumstances where post-Newtonian corrections are vanishingly small, strong concordance with Newton and Kepler except at the lowest accelerations.
The orbits of galactic blobs of slowly-moving molecular gas that produce characteristic spectral lines amenable to Doppler redshift study are almost always in those special circumstances, and they have higher accelerations "corewards" in galaxies and low accelerations "outwards" in galaxies. These gas blobs are most interesting at the leading and trailing limbs of edge-on discoid/spiral galaxies, or face-on in large elliptical galaxies with negligible bulk rotation (the Doppler-shifting blobs move in and out, almost entirely radially), precisely where the accelerations are smallest.
The question we then ask is: what if we have a blob or some other spectrally well-defined object in a galaxy is on a very fast orbit? We can no longer ignore post-Newtonian corrections, or we lose the MONDian match with spectral lines. This is what drives §7 ibid.
If we think of the expansion as:
Total gravitation = empty flat background + MONDian matter relation + higher-order terms (h.-o.t.s. or HOTs)
the relativistically moving but still-MONDian matter is the generator of the HOTs, which has been measured (by among other people Pavel Kroupa, the author of the fine article at the top of all this discussion).
Abandoning the MONDian matter relation is easy. Just recast:
Total Einstein gravitation = empty flat background + unknown stress-energy tensor + higher-order terms
and adapt the stress-energy tensor. Nothing in the theory of gravitation has ever suggested strongly the nature of matter which generates the stress-energy, but we can get constraints from other areas of physics like the standard model of particle physics (or even classical electromagnetism, as was the case when General Relativity was new), and we can get candidates from programs seeking to expand or alter the Standard Model to solve open non-gravitational problems. Thus: various types of electrically-neutral particles like axions or supersymmetrical sparticles have been considered because "someone else" (i.e., not a relativist) hypothesized them. (Observational cosmologists can find evidence to constrain such theories, and in practice helped kill off several supersymmetry extensions of the standard model, for example). Low-mass primordial black holes were a candidate too, because there were non-galactic-dynamics reasons to suspect they could exist in significant number. But those black holes (or very dim tiny stars or isolated cold Jupiters) could maybe generate the unknown stress-energy tensor.
Retaining the MONDian approach can be done in a couple of ways. Hold to the idea that the "luminous" stuff is the only source of gravitation, and then ask whether relativistically-moving MONDian matter is coupled to an unexpected background:
Total gravitation = empty flat background + curvature corrections + MONDian matter + HOTs
(where all that's left in HOTs is basically gravitational waves from relativistically-moving MONDian matter)
or alternatively whether there is a further field or fields to which slow-moving MONDian matter couples only very weakly, but fast-moving MONDian matter experiences quite strongly. That means the HOTs imply the existence of one or more new fields.
Are these fields free parameters? Good (and open) question.
What types of fields are allowed? §7 ibid. explores this largely in terms of adding fields to the Einstein Field Equations (EFEs) of general relativity. The fields conceptually modify Einsteinian gravitation, so are written on the curvature side of the EFEs. However, as the authors of the survey note, in most cases for purely mathematical reasons the fields could be written exactly equivalently as a function on the stress-energy tensor (the matter side of the curvature = matter relation).
Why are we thinking in terms of an adaptation of the Einstein Field equation in the first place? Because it works well for length scales much shorter than ~ten kiloparsecs, and might work well for length scales much greater than megaparsecs. In particular, it works so well in the solar system that it cannot be ignored: it is the effective theory of gravitation near us. So however one might eventually write down a relativistic MOND theory, it must be possible to re-write it into a modification of the Einstein Field Equations for use in the solar system and in systems like Hulse-Taylor or triple-pulsar J0337+1715.
Additionally, analysis through tools like the Parameterized post-Newtonian formalism <https://en.wikipedia.org/wiki/Alternatives_to_general_relati...> is extremely useful if one recasts some arbitrarily-different-from-General-Relativity gravitational theory into something for which PPNF variables can be found. The discipline of submitting to PPNF by rewriting a theory for PPNF friendliness often is personally useful for the theorist keenly interested in her or his not-like-General-Relativity theory of gravitation.
One might say, aiming for neutrality, that if one adapts the EFEs in such a way that the adaptation can appear on either side of the EFEs, the "conceptual" weight of the adaptation is perhaps more aesthetic than physical.
However, that's not quite fair: outright adding extra stress-energy dark-matter-style lets one decouple the "adaptation" of the galactic relation from galaxies themselves. One could put particle dark matter in parts of the universe where there are no electrons or protons. For instance, before electroweak decoupling and big bang baryogenesis, or in the extreme distant future where we have basically isolated black holes and relic microwaves (and neutrinos) that are undetectably cold/long-wavelength. Even around "today"'s epoch, dark matter could be put willy nilly well away from clusters of galaxies.
A modified gravity theory, relativized along the lines of Famaey and McGaugh's surveyed options, might also be able to do this. Strange curvature just existing apart from any matter. (One can do this by a choice of a strange background in a post-Newtonian correction formulation of standard General Relativity too.) But to be MONDian I think that you would want attractive gravitation to appear only where there is matter that interacts electromagnetically, because far from such matter (attractive) accelerations will be very low, and the central feature of MOND is that Newtonian gravitation needs adjustment at very low accelerations.
So for a fully-relativistic MONDian theory of gravitation, although maybe mathematically we could treat the low-acceleration as a field that we could drop just about anywhere, doing so would violate MOND's spirit. There is thus no vacuum + MOND field(s) gravitational solution that is remotely physical. This is certainly not the case for particle theories of dark matter. Those basically insist that it is perfectly reasonable to drop dark matter just about anywhere. One can easily expect to simulate a vacuum + cold dark matter solution to the Einstein Field Equations, and that the simulation might accord with some part of our actual universe.
Finally, without further diving into the aesthetics or bets about what particle physics at CERN and the like might discover about mechanisms that generate stress-energy, I think the "fight" between MONDian modified gravitation and Einsteinian gravitation with dark matter is irrelevant to astrophysicists (as opposed to theorists who deal with non-astrophysical systems), even those who work on galaxy dynamics. It is almost certain that it will be possible to find an initial values formulation for either type of "final conceptual" answer to the observed Milgrom relation. It's just a question then of finding out how to populate the initial values surface, and then letting the dynamical laws go to work on those.
(The initial data and laws for each theory (MOND or GR+DM) reformulated this way will necessarily differ, perhaps by a lot, but the approach of evolving a set of initial data will be the same (this is done in many areas of physics having little/nothing to do with gravitation, after all)).
That is, the core of the MOND/particle DM fight might be more about bets on whether the single minimally-coupled metric tensor approach in General Relativity is not always suitable, or whether the Standard Model of particle physics is incomplete in relevant ways, than about whether one is really more suitable for calculations than the other. (The bet is also not strictly either/or!)
I'm honestly not sure who will really care in practice, if it's ever "finally" decided one way or another.
Those characteristics are: no "non-luminous" or "hidden" matter sources -- the glowing, refracting, and obscuring dusts are the sole sources of gravitation -- and in circumstances where post-Newtonian corrections are vanishingly small, strong concordance with Newton and Kepler except at the lowest accelerations.
The orbits of galactic blobs of slowly-moving molecular gas that produce characteristic spectral lines amenable to Doppler redshift study are almost always in those special circumstances, and they have higher accelerations "corewards" in galaxies and low accelerations "outwards" in galaxies. These gas blobs are most interesting at the leading and trailing limbs of edge-on discoid/spiral galaxies, or face-on in large elliptical galaxies with negligible bulk rotation (the Doppler-shifting blobs move in and out, almost entirely radially), precisely where the accelerations are smallest.
The question we then ask is: what if we have a blob or some other spectrally well-defined object in a galaxy is on a very fast orbit? We can no longer ignore post-Newtonian corrections, or we lose the MONDian match with spectral lines. This is what drives §7 ibid.
If we think of the expansion as:
Total gravitation = empty flat background + MONDian matter relation + higher-order terms (h.-o.t.s. or HOTs)
the relativistically moving but still-MONDian matter is the generator of the HOTs, which has been measured (by among other people Pavel Kroupa, the author of the fine article at the top of all this discussion).
Abandoning the MONDian matter relation is easy. Just recast:
Total Einstein gravitation = empty flat background + unknown stress-energy tensor + higher-order terms
and adapt the stress-energy tensor. Nothing in the theory of gravitation has ever suggested strongly the nature of matter which generates the stress-energy, but we can get constraints from other areas of physics like the standard model of particle physics (or even classical electromagnetism, as was the case when General Relativity was new), and we can get candidates from programs seeking to expand or alter the Standard Model to solve open non-gravitational problems. Thus: various types of electrically-neutral particles like axions or supersymmetrical sparticles have been considered because "someone else" (i.e., not a relativist) hypothesized them. (Observational cosmologists can find evidence to constrain such theories, and in practice helped kill off several supersymmetry extensions of the standard model, for example). Low-mass primordial black holes were a candidate too, because there were non-galactic-dynamics reasons to suspect they could exist in significant number. But those black holes (or very dim tiny stars or isolated cold Jupiters) could maybe generate the unknown stress-energy tensor.
Retaining the MONDian approach can be done in a couple of ways. Hold to the idea that the "luminous" stuff is the only source of gravitation, and then ask whether relativistically-moving MONDian matter is coupled to an unexpected background:
Total gravitation = empty flat background + curvature corrections + MONDian matter + HOTs
(where all that's left in HOTs is basically gravitational waves from relativistically-moving MONDian matter)
or alternatively whether there is a further field or fields to which slow-moving MONDian matter couples only very weakly, but fast-moving MONDian matter experiences quite strongly. That means the HOTs imply the existence of one or more new fields.
Are these fields free parameters? Good (and open) question.
What types of fields are allowed? §7 ibid. explores this largely in terms of adding fields to the Einstein Field Equations (EFEs) of general relativity. The fields conceptually modify Einsteinian gravitation, so are written on the curvature side of the EFEs. However, as the authors of the survey note, in most cases for purely mathematical reasons the fields could be written exactly equivalently as a function on the stress-energy tensor (the matter side of the curvature = matter relation).
Why are we thinking in terms of an adaptation of the Einstein Field equation in the first place? Because it works well for length scales much shorter than ~ten kiloparsecs, and might work well for length scales much greater than megaparsecs. In particular, it works so well in the solar system that it cannot be ignored: it is the effective theory of gravitation near us. So however one might eventually write down a relativistic MOND theory, it must be possible to re-write it into a modification of the Einstein Field Equations for use in the solar system and in systems like Hulse-Taylor or triple-pulsar J0337+1715.
Additionally, analysis through tools like the Parameterized post-Newtonian formalism <https://en.wikipedia.org/wiki/Alternatives_to_general_relati...> is extremely useful if one recasts some arbitrarily-different-from-General-Relativity gravitational theory into something for which PPNF variables can be found. The discipline of submitting to PPNF by rewriting a theory for PPNF friendliness often is personally useful for the theorist keenly interested in her or his not-like-General-Relativity theory of gravitation.
One might say, aiming for neutrality, that if one adapts the EFEs in such a way that the adaptation can appear on either side of the EFEs, the "conceptual" weight of the adaptation is perhaps more aesthetic than physical.
However, that's not quite fair: outright adding extra stress-energy dark-matter-style lets one decouple the "adaptation" of the galactic relation from galaxies themselves. One could put particle dark matter in parts of the universe where there are no electrons or protons. For instance, before electroweak decoupling and big bang baryogenesis, or in the extreme distant future where we have basically isolated black holes and relic microwaves (and neutrinos) that are undetectably cold/long-wavelength. Even around "today"'s epoch, dark matter could be put willy nilly well away from clusters of galaxies.
A modified gravity theory, relativized along the lines of Famaey and McGaugh's surveyed options, might also be able to do this. Strange curvature just existing apart from any matter. (One can do this by a choice of a strange background in a post-Newtonian correction formulation of standard General Relativity too.) But to be MONDian I think that you would want attractive gravitation to appear only where there is matter that interacts electromagnetically, because far from such matter (attractive) accelerations will be very low, and the central feature of MOND is that Newtonian gravitation needs adjustment at very low accelerations.
So for a fully-relativistic MONDian theory of gravitation, although maybe mathematically we could treat the low-acceleration as a field that we could drop just about anywhere, doing so would violate MOND's spirit. There is thus no vacuum + MOND field(s) gravitational solution that is remotely physical. This is certainly not the case for particle theories of dark matter. Those basically insist that it is perfectly reasonable to drop dark matter just about anywhere. One can easily expect to simulate a vacuum + cold dark matter solution to the Einstein Field Equations, and that the simulation might accord with some part of our actual universe.
Finally, without further diving into the aesthetics or bets about what particle physics at CERN and the like might discover about mechanisms that generate stress-energy, I think the "fight" between MONDian modified gravitation and Einsteinian gravitation with dark matter is irrelevant to astrophysicists (as opposed to theorists who deal with non-astrophysical systems), even those who work on galaxy dynamics. It is almost certain that it will be possible to find an initial values formulation for either type of "final conceptual" answer to the observed Milgrom relation. It's just a question then of finding out how to populate the initial values surface, and then letting the dynamical laws go to work on those.
(The initial data and laws for each theory (MOND or GR+DM) reformulated this way will necessarily differ, perhaps by a lot, but the approach of evolving a set of initial data will be the same (this is done in many areas of physics having little/nothing to do with gravitation, after all)).
That is, the core of the MOND/particle DM fight might be more about bets on whether the single minimally-coupled metric tensor approach in General Relativity is not always suitable, or whether the Standard Model of particle physics is incomplete in relevant ways, than about whether one is really more suitable for calculations than the other. (The bet is also not strictly either/or!)
I'm honestly not sure who will really care in practice, if it's ever "finally" decided one way or another.
> So however one might eventually write down a relativistic MOND theory, it must be possible to re-write it into a modification of the Einstein Field Equations for use in the solar system and in systems like Hulse-Taylor or triple-pulsar J0337+1715.
This is the contention I have with the "fine-tune" argument against DM: there's still tuning needed from the MOND side to both make it a predictable tool across the universe and also ensure it still acts like EFE at home. Everybody's tuning/tweaking because no one has anything novel.
To bring in an interesting analogy: it's almost like the debate over functional and OO programming paradigms. MOND seeks to tune the "function" or theory to better fit all observations. DM seeks to tune the "objects" or observations to better fit the theory.
This is the contention I have with the "fine-tune" argument against DM: there's still tuning needed from the MOND side to both make it a predictable tool across the universe and also ensure it still acts like EFE at home. Everybody's tuning/tweaking because no one has anything novel.
To bring in an interesting analogy: it's almost like the debate over functional and OO programming paradigms. MOND seeks to tune the "function" or theory to better fit all observations. DM seeks to tune the "objects" or observations to better fit the theory.
> This is the contention I have with the "fine-tune" argument against DM: there's still tuning needed from the MOND side to both make it a predictable tool across the universe and also ensure it still acts like EFE at home.
The whole point of MOND is that our gravitational theory is inadequate, and exploring what modifications are needed to match observations is the way move forward, rather than assuming GR is correct and searching for the missing mass it says should be there. We actually already know GR must be wrong because of its singularities, so this insistence on looking for DM despite the constant failures is doubly strange.
MOND's process of exploring what modifications are needed isn't "fine-tuning" in the way that DM has been tuned because MOND is not a final or complete theory, and nobody has presented it as such.
The whole point of MOND is that our gravitational theory is inadequate, and exploring what modifications are needed to match observations is the way move forward, rather than assuming GR is correct and searching for the missing mass it says should be there. We actually already know GR must be wrong because of its singularities, so this insistence on looking for DM despite the constant failures is doubly strange.
MOND's process of exploring what modifications are needed isn't "fine-tuning" in the way that DM has been tuned because MOND is not a final or complete theory, and nobody has presented it as such.
> We actually already know GR must be wrong because of its singularities
This is not why we "know" GR must be wrong.
You keep making very strong assertions that any expert -- including those not hostile to MOND, or even positively in favour of properly capturing the empirical MOND relation into some other theory (whether that's the standard one or one like Bekenstein's) -- simply would not make.
I do not know what you are trying to do here on HN, but it does not seem to be an attempt to honestly help people who are interested in dark matter but who lack expertise; it doesn't seem to be an attempt to acquire expertise you clearly lack; and it doesn't seem to be an attempt to work out how you yourself might better understand difficult concepts through a process of ELI5/ELI12. It seems, frankly, like you just enjoy being rude on hackernews.
In order to make up for the observations above that might be fairly taken as leading off with insults, I'll supply some related real, standard, uncontroversial physics discussion.
The principal problem with General Relativity is that the stress-energy tensor when generated by real matter (which we know can behave quantum mechanically) must in principle be able to encode superpositions of (at least) spin, momentum, and position. However, the Einstein Field Equations are fully classical, so how to do this encoding is not known. As a result "hacks" like taking the expectation value of the stress-energy T_{\mu\nu} -> <T_{\mu\nu}> are used to make the EFEs work at all. Unfortunately this averaging generally destroys superpositions, so one runs into problems like: if we took a fairly large molecule and put it into a superposition of position in a laboratory full of sensitive precision-stabilized accelerometers, what should we expect them to show? To which the answers are unattractive (and hopefully will be tested soon enough by direct experiment (at e.g. <https://www.npl.washington.edu/eotwash/node/1>)). A little more detail in <https://en.wikipedia.org/wiki/Semiclassical_gravity> or for more advanced readers e.g. <https://journals.aps.org/prd/abstract/10.1103/PhysRevD.47.45...> which corresponds with <https://arxiv.org/abs/gr-qc/9304008>.
This is far far far from the strong gravity regime near gravitational singularities. It's a problem we could test in a spacecraft in deep space, or in a laboratory here on Earth. No black holes required.
Singularities, while annoying for developing Cauchy problems as one likes to do in many areas of physics, are not immediately fatal to the theory for several reasons, including the probable correctness of the cosmic censorship hypothesis and the long term stability of realistic black holes. Indeed, at least General Relativity is a complete theory that makes a prediction about what happens at its highest energy levels (measured in curvature invariants, like Kretschmann's). The Standard Model of Particle Physics is not presently "UV-complete". (More details @ <https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Mo...>, "The Standard Model is inherently an incomplete theory.") The converse is that while General Relativity is an inherently complete theory, it requires care in encoding the stress-energy tensor, any "background" curvature, boundary conditions, constraints, energy and coordinate conditions, and so forth. It is not an easy theory at all, especially when one does not understand all the mechanisms that generate the stress-energy tensor. Its successes as an effective field theory in astrophysical applications are legion, and completely contradict the remainder of your second paragraph.
All of the above equally applies to relativistic MOND (except the last sentence of the preceding paragraph: relativistic MOND generically gets the acoustic peaks of the CMB temperature power spectrum wrong, and usually badly wrong for the odd-numbered peaks, principally and importantly because of how different MOND is, by design, at assigning pressure in equations-of-state, and how that matters before the formation of the first galaxies). Milgrom's work has afaik always been in the regime where quantum weirdness has been negligible (and indeed, for most of MOND's history was even wholly in the regime where special-relativistic weirdness was negligible).
MOND has been explored for more than fifty years, and Relativistic MOND for more than twenty years, by some of the biggest brains in gravitational physics, including Mordehai Milgrom <https://arxiv.org/abs/1310.3373>. There are endless publications about MOND even today (tiny sample: <https://arxiv.org/search/advanced?advanced=&terms-0-operator...>). Nobody working in galactic astrophysics is ignorant of it, or of the phenomenological Milgrom's law. Most theorists working in gravitation have played with it so they already know:
> exploring what modifications are needed to match observations is the way forward
So I find myself wondering: do you genuinely not know that MOND "is a thing" already (and has been for decades) in the relevant academic and professional circles?
This is not why we "know" GR must be wrong.
You keep making very strong assertions that any expert -- including those not hostile to MOND, or even positively in favour of properly capturing the empirical MOND relation into some other theory (whether that's the standard one or one like Bekenstein's) -- simply would not make.
I do not know what you are trying to do here on HN, but it does not seem to be an attempt to honestly help people who are interested in dark matter but who lack expertise; it doesn't seem to be an attempt to acquire expertise you clearly lack; and it doesn't seem to be an attempt to work out how you yourself might better understand difficult concepts through a process of ELI5/ELI12. It seems, frankly, like you just enjoy being rude on hackernews.
In order to make up for the observations above that might be fairly taken as leading off with insults, I'll supply some related real, standard, uncontroversial physics discussion.
The principal problem with General Relativity is that the stress-energy tensor when generated by real matter (which we know can behave quantum mechanically) must in principle be able to encode superpositions of (at least) spin, momentum, and position. However, the Einstein Field Equations are fully classical, so how to do this encoding is not known. As a result "hacks" like taking the expectation value of the stress-energy T_{\mu\nu} -> <T_{\mu\nu}> are used to make the EFEs work at all. Unfortunately this averaging generally destroys superpositions, so one runs into problems like: if we took a fairly large molecule and put it into a superposition of position in a laboratory full of sensitive precision-stabilized accelerometers, what should we expect them to show? To which the answers are unattractive (and hopefully will be tested soon enough by direct experiment (at e.g. <https://www.npl.washington.edu/eotwash/node/1>)). A little more detail in <https://en.wikipedia.org/wiki/Semiclassical_gravity> or for more advanced readers e.g. <https://journals.aps.org/prd/abstract/10.1103/PhysRevD.47.45...> which corresponds with <https://arxiv.org/abs/gr-qc/9304008>.
This is far far far from the strong gravity regime near gravitational singularities. It's a problem we could test in a spacecraft in deep space, or in a laboratory here on Earth. No black holes required.
Singularities, while annoying for developing Cauchy problems as one likes to do in many areas of physics, are not immediately fatal to the theory for several reasons, including the probable correctness of the cosmic censorship hypothesis and the long term stability of realistic black holes. Indeed, at least General Relativity is a complete theory that makes a prediction about what happens at its highest energy levels (measured in curvature invariants, like Kretschmann's). The Standard Model of Particle Physics is not presently "UV-complete". (More details @ <https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Mo...>, "The Standard Model is inherently an incomplete theory.") The converse is that while General Relativity is an inherently complete theory, it requires care in encoding the stress-energy tensor, any "background" curvature, boundary conditions, constraints, energy and coordinate conditions, and so forth. It is not an easy theory at all, especially when one does not understand all the mechanisms that generate the stress-energy tensor. Its successes as an effective field theory in astrophysical applications are legion, and completely contradict the remainder of your second paragraph.
All of the above equally applies to relativistic MOND (except the last sentence of the preceding paragraph: relativistic MOND generically gets the acoustic peaks of the CMB temperature power spectrum wrong, and usually badly wrong for the odd-numbered peaks, principally and importantly because of how different MOND is, by design, at assigning pressure in equations-of-state, and how that matters before the formation of the first galaxies). Milgrom's work has afaik always been in the regime where quantum weirdness has been negligible (and indeed, for most of MOND's history was even wholly in the regime where special-relativistic weirdness was negligible).
MOND has been explored for more than fifty years, and Relativistic MOND for more than twenty years, by some of the biggest brains in gravitational physics, including Mordehai Milgrom <https://arxiv.org/abs/1310.3373>. There are endless publications about MOND even today (tiny sample: <https://arxiv.org/search/advanced?advanced=&terms-0-operator...>). Nobody working in galactic astrophysics is ignorant of it, or of the phenomenological Milgrom's law. Most theorists working in gravitation have played with it so they already know:
> exploring what modifications are needed to match observations is the way forward
So I find myself wondering: do you genuinely not know that MOND "is a thing" already (and has been for decades) in the relevant academic and professional circles?
> This is not why we "know" GR must be wrong.
I don't at all dispute that GR is very well confirmed in many regimes, but it's still an indisputable fact is that GR is definitely wrong because of its singularities. Whether it's wrong in other regimes remains to be seen.
Some like to reframe its breakdown as GR being "incomplete", but that's just a cute euphemism for "wrong". This point couldn't be more obvious so I'm not even sure why you would dispute it.
You can of course argue that GR may only be wrong on small scales or very high energies where quantum effects become relevant, but that's just conjecture. A conjecture with good reasons given GR's empirical success so far, but still not established fact.
How GR fails may or may not impact the argument for DM, but we should acknowledge that the fact that GR is wrong actually might impact the justification for DM, which should already make us more skeptical of the core case for DM.
> So I find myself wondering: do you genuinely not know that MOND "is a thing" already (and has been for decades) in the relevant academic and professional circles?
Of course it's a thing. I'm not sure how I can be more clear on what arguing, so I'll try one last time: while I appreciate the interesting details you've put into your replies, nothing you've said changes the fact that DM's highly regarded status in this field is just undeserved, and that MOND still gets less attention than it deserves given its unexpected predictive successes [3,4].
DM was very plausible early on, but it has repeatedly failed to provide clear predictions and failed to match observations without post-hoc adjustments, where MOND has had some very surprising predictions that matched observations in ways it had no right to if DM were true. I don't believe I ever disputed that MOND also required tuning to match some results, so clearly neither theory is adequate to explain all of our observations in their current forms. At the very least we should be able to agree on that.
Other specific points:
TeVeS is one relativistic generalization of MOND, but hardly the only one possible is it? How much attention has been paid to MOND and relativistic generalizations when compared to tweaking DM theories to match results, would you say? Wouldn't you agree that all of the attention to DM, and the dogma that DM must simply exist [1], detracts from exploring other possible avenues, like questioning assumptions that underlie our theories, as in [2]?
On a final point on tone, I have no idea what you mean by me being enjoying being rude. I haven't said a single rude thing that I can see, I've only disagreed with some interpretations of the data and claimed that DM enjoys an undeserved status as preferred model, and that MOND deserves more attention, all positions with ample evidence.
[1] https://www.preposterousuniverse.com/blog/2011/02/26/dark-ma...
[2] https://www.mdpi.com/2075-4434/9/4/76/htm
[3] http://astroweb.case.edu/ssm/mond/LCDMmondtesttable.html
[4] http://astroweb.case.edu/ssm/mond/Claim-Rebuttal.pdf
I don't at all dispute that GR is very well confirmed in many regimes, but it's still an indisputable fact is that GR is definitely wrong because of its singularities. Whether it's wrong in other regimes remains to be seen.
Some like to reframe its breakdown as GR being "incomplete", but that's just a cute euphemism for "wrong". This point couldn't be more obvious so I'm not even sure why you would dispute it.
You can of course argue that GR may only be wrong on small scales or very high energies where quantum effects become relevant, but that's just conjecture. A conjecture with good reasons given GR's empirical success so far, but still not established fact.
How GR fails may or may not impact the argument for DM, but we should acknowledge that the fact that GR is wrong actually might impact the justification for DM, which should already make us more skeptical of the core case for DM.
> So I find myself wondering: do you genuinely not know that MOND "is a thing" already (and has been for decades) in the relevant academic and professional circles?
Of course it's a thing. I'm not sure how I can be more clear on what arguing, so I'll try one last time: while I appreciate the interesting details you've put into your replies, nothing you've said changes the fact that DM's highly regarded status in this field is just undeserved, and that MOND still gets less attention than it deserves given its unexpected predictive successes [3,4].
DM was very plausible early on, but it has repeatedly failed to provide clear predictions and failed to match observations without post-hoc adjustments, where MOND has had some very surprising predictions that matched observations in ways it had no right to if DM were true. I don't believe I ever disputed that MOND also required tuning to match some results, so clearly neither theory is adequate to explain all of our observations in their current forms. At the very least we should be able to agree on that.
Other specific points:
TeVeS is one relativistic generalization of MOND, but hardly the only one possible is it? How much attention has been paid to MOND and relativistic generalizations when compared to tweaking DM theories to match results, would you say? Wouldn't you agree that all of the attention to DM, and the dogma that DM must simply exist [1], detracts from exploring other possible avenues, like questioning assumptions that underlie our theories, as in [2]?
On a final point on tone, I have no idea what you mean by me being enjoying being rude. I haven't said a single rude thing that I can see, I've only disagreed with some interpretations of the data and claimed that DM enjoys an undeserved status as preferred model, and that MOND deserves more attention, all positions with ample evidence.
[1] https://www.preposterousuniverse.com/blog/2011/02/26/dark-ma...
[2] https://www.mdpi.com/2075-4434/9/4/76/htm
[3] http://astroweb.case.edu/ssm/mond/LCDMmondtesttable.html
[4] http://astroweb.case.edu/ssm/mond/Claim-Rebuttal.pdf
Hands up everybody that understood all that...
I agree. I find it hard to argue against the claim that all physics is just curve fitting. We always end up with tuned parameters to make the maths work. For example the G in F = Gmm/r^2 (Newtonian mechanics).
I'm not an expert, but it seems like Dark Matter theories allow the DM distribution to be tuned. Is that the case? Can you say, "oh, there must be a clump of DM over here with mass X". If so, that would give you lots of parameters to tune per situation you're modelling. It may be that IS how the universe works. The problem is that the theory is hard to falsify if it has so much wiggle room to fit every situation.
I'm not an expert, but it seems like Dark Matter theories allow the DM distribution to be tuned. Is that the case? Can you say, "oh, there must be a clump of DM over here with mass X". If so, that would give you lots of parameters to tune per situation you're modelling. It may be that IS how the universe works. The problem is that the theory is hard to falsify if it has so much wiggle room to fit every situation.
Fine tuning usually means some kind of teleological goal, not merely uniqueness of present state.
Same way normal matter has a clump here or a galaxy there or a super cluster over there.
Except we don't get to invent where they are because you can see normal matter. We tried before to invent some normal matter to explain the orbit of Mercury. https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet).
sure, but you didn't get the point. just because a model can predict certain results doesn't mean its correct. early astronomers were able to very precisely predict the positions (w/ looping motions and all) of stellar bodies in the night sky despite using a geocentric model. if you make it complex enough, you can engineer quite a few models that can predict natural phenomenon pretty well.
Yes of course, but this applies to any model. We cannot know of any model is "correct", they are just tools to describe what we observe. If they are more predictive than other models, then we should use them. Or course it's better to use a simpler model that gives the same predictions.
> if you make it complex enough, you can engineer quite a few models that can predict natural phenomenon pretty well.
Well, yes. Next thing is to pick the easiest of these models: Occam's razor. But pondering whether such model is "correct" won't bring any further improvements.
Well, yes. Next thing is to pick the easiest of these models: Occam's razor. But pondering whether such model is "correct" won't bring any further improvements.
If this is true, then were epicycle models physics? How about the luminiferous aether?
I worked in this field for a minute (XENON1T) and I heard a few talks about MOND. We were all pretty open minded but it failed to stick because it didn’t convince us, for a number of reasons. Curious about your background here.
> MOND has more points in favour for it as a preferred theory than DM models.
Isn't MOND completely falsified by the discovery of galaxies without dark matter?
Isn't MOND completely falsified by the discovery of galaxies without dark matter?
It was already falsified by well established limits on self interaction of DM from galaxy collisions. And from the already mentioned temperature fluctuations in the CMB. Every now and then some MOND supporter comes out if they found a way to tune their model to one specific observation, but particle DM remains the only approach that can fit all these observations at the same time. Ofc that doesn't guarantee that particle DM is the only explanation. After all, it could be a combination of DM+MOND. But MOND alone is just not possible, whereas DM alone might be.
By that argument, DM was already falsified by the observations pointed out in this article and the paper I linked. Your claim that DM could "fit all of these observations at the same time" is just wrong. DM has been tuned to correct its parameter-free predictions, so if you're going to compare like against like, then MOND should be permitted to be tuned to fit as well, and we can judge in the end which theory requires the least fine-tuning.
As for galaxies without DM, those observations are still being debated, but even if true, that doesn't entail MOND can't explain those results.
As for galaxies without DM, those observations are still being debated, but even if true, that doesn't entail MOND can't explain those results.
I don't think it's fair to say that it's "tuned" to fit observation. It's not like several different types of DM are introduced to fit the observation. Rather the observations add some constraints to the DM properties. That's how it's supposed to be.
If DM has to have a very specific initial distribution to reproduce what we see, for example, that too is a constraint but it's also fine-tuning. Another theory that is free of such parameters should be preferred. Some types of constraints really should decrease a theory's plausibility.
MOND needs some pretty crazy arguing to explain decoupling of gravity from baryonic matter distributions. And it also needs a varying length scale parameter to account for different galaxy types. Particle DM can explain all of these things at the same time without re-tuning the model every time.
> MOND needs some pretty crazy arguing to explain decoupling of gravity from baryonic matter distributions. And it also needs a varying length scale parameter to account for different galaxy types.
You mean the theory that has received 2-3 orders of magnitude less attention than DM has some conceptual holes to patch up? Colour me shocked. The fact that DM still fails despite all of that investment should worry you more.
> Particle DM can explain all of these things at the same time without re-tuning the model every time.
DM has already been tweaked and fine-tuned to patch up its own endless list of holes, many of which were recently reviewed by McGaugh [1]. Many more remain despite that, like the dynamical friction discussed in this article.
[1] https://tritonstation.com/2022/04/08/two-hypotheses/
You mean the theory that has received 2-3 orders of magnitude less attention than DM has some conceptual holes to patch up? Colour me shocked. The fact that DM still fails despite all of that investment should worry you more.
> Particle DM can explain all of these things at the same time without re-tuning the model every time.
DM has already been tweaked and fine-tuned to patch up its own endless list of holes, many of which were recently reviewed by McGaugh [1]. Many more remain despite that, like the dynamical friction discussed in this article.
[1] https://tritonstation.com/2022/04/08/two-hypotheses/
Here's an explanation why McGaugh's work is highly dubious: https://www.preposterousuniverse.com/blog/2011/02/26/dark-ma... It also talks about the general problems with alternatives to particle DM.
Sean's breakdown is ironic, because every point he makes against MOND also applies to DM theories, particularly given new evidence. I have no problem acknowledging that MOND is inadequate given the data, but apparently it's difficult for DM supporters to similarly acknowledge that DM has been refuted. The core argument for DM rests on a theory (GR) that we already know must be incorrect due to its singularities.
Finally, I'll just note that literally nothing in Sean's post suggests McGaugh's work is "dubious" in the least, so I have no idea where you got that notion.
Finally, I'll just note that literally nothing in Sean's post suggests McGaugh's work is "dubious" in the least, so I have no idea where you got that notion.
The best thing this article can provide is that some galaxies work without DM. Only particle DM can explain the early universe observations from the CMB (which this article completely glosses over), decoupling from baryonic matter (which also isn't even mentioned) and galaxy rotation curves at the same time. The arguments in favour of DM are far more general and rightly accepted for what they are, whereas the sporadic argument for MOND that works in one domain is rightly shunned as long as its proponents blissfully keep ignoring the overwhelming incompatibilities in the remaining domains.
> Only particle DM can explain the early universe observations from the CMB
Are you actually arguing that DM is the only conceivable theory that can possibly explain those observations? Be serious. This obsession with DM when it's been clearly falsified numerous times is restricting imagination and attention on novel approaches.
Are you actually arguing that DM is the only conceivable theory that can possibly explain those observations? Be serious. This obsession with DM when it's been clearly falsified numerous times is restricting imagination and attention on novel approaches.
I explicitly said it might very well not be the only one. But the data clearly shows that MOND is definitely not the only one. Since Occam's Razor tells us to go with the simplest solution, science goes for DM, instead of DM+MOND. If we ever discover DM (eg in the form of WIMPs) and it can't account for all the extra mass in the universe, then people will be able to look closer at modified gravity again. But right now these models are just not at a point where they could explain more than noise. If you're interested in how difficult it actually is to come up with a robust alternative theory of gravity that can fully explain all aspects of DM we see in the universe, I suggest this lecture here: https://www.youtube.com/watch?v=WECVq2YBduY tl;dr: it's hard. Very hard. Noone has done it yet.
> I explicitly said it might very well not be the only one.
Actually you didn't. Perhaps you claimed that in another thread, but I quoted exactly what you wrote in this thread, which is that only DM can explain those results.
> Since Occam's Razor tells us to go with the simplest solution, science goes for DM, instead of DM+MOND.
That's not a correct formulation of Occam's razor. Occam's razor tells us not to posit the existence of more things than are necessary to explain observations. Observations already tell us that DM either does not exist, or doesn't exist in the amounts most people think exists, ie. most DM models have been refuted. Therefore, even if DM exists, something else is still needed to explain our observations.
Actually you didn't. Perhaps you claimed that in another thread, but I quoted exactly what you wrote in this thread, which is that only DM can explain those results.
> Since Occam's Razor tells us to go with the simplest solution, science goes for DM, instead of DM+MOND.
That's not a correct formulation of Occam's razor. Occam's razor tells us not to posit the existence of more things than are necessary to explain observations. Observations already tell us that DM either does not exist, or doesn't exist in the amounts most people think exists, ie. most DM models have been refuted. Therefore, even if DM exists, something else is still needed to explain our observations.
>Observations already tell us that DM either does not exist
This is just a plain lie and since you obviously have no interest in further educating yourself in any way, I will now stop wasting my time with replying to you.
This is just a plain lie and since you obviously have no interest in further educating yourself in any way, I will now stop wasting my time with replying to you.
Convenient you omit the other possibility. But sure, bury your head in the sand of the prevailing evidence reviewed in the paper I linked.
As my understanding goes the models used are there to see what would be needed to replicate the current best know state of the universe, given what we know about its beginnings and as said its "current" state. Running very many different scenarios the best models need something the astro "community" came to call "dark matter".
As long as a opposing theory can't replicate these simulations from initial state to known "now" state without the use of some form of "whatever" it is quite interesting to call out that there is nothing like "dark matter" (whatever this something may be).
But that is just my layman's take.
As long as a opposing theory can't replicate these simulations from initial state to known "now" state without the use of some form of "whatever" it is quite interesting to call out that there is nothing like "dark matter" (whatever this something may be).
But that is just my layman's take.
> This is the same shtick from from a known anti-DM guy.
Whether it's a "shtick" or not, his basic point seems like one that is worthy of some kind of substantive counter argument, if one exists. His basic point is that small galaxies orbiting larger galaxies should experience Chandrasekhar dynamical friction if dark matter exists, but no such thing is observed. Therefore dark matter cannot exist.
Has any astrophysicist who supports the dark matter hypothesis published a counter argument to this?
Edit: A published paper of Kroupa's that gives much more detail about his point is here:
https://arxiv.org/pdf/1406.4860.pdf
Whether it's a "shtick" or not, his basic point seems like one that is worthy of some kind of substantive counter argument, if one exists. His basic point is that small galaxies orbiting larger galaxies should experience Chandrasekhar dynamical friction if dark matter exists, but no such thing is observed. Therefore dark matter cannot exist.
Has any astrophysicist who supports the dark matter hypothesis published a counter argument to this?
Edit: A published paper of Kroupa's that gives much more detail about his point is here:
https://arxiv.org/pdf/1406.4860.pdf
> Therefore dark matter cannot exist.
How about therefore thing we've yet to observe if it exists fails to behave as we naively expect.
This is a grand claim from one piece of work and feels more like a straw man grab at further research funding rather than finding the heffalon at the LHC https://arxiv.org/abs/1303.7367
Or in other words Occam's razor says you have a stripey horse in northern Europe rather than a zebra.
How about therefore thing we've yet to observe if it exists fails to behave as we naively expect.
This is a grand claim from one piece of work and feels more like a straw man grab at further research funding rather than finding the heffalon at the LHC https://arxiv.org/abs/1303.7367
Or in other words Occam's razor says you have a stripey horse in northern Europe rather than a zebra.
> How about therefore thing we've yet to observe if it exists fails to behave as we naively expect.
As I understand it, the "behavior" of dark matter in Kroupa's analysis is the behavior that is claimed for it by dark matter proponents. So if dark matter doesn't behave the way dark matter proponents say it does, the burden would be on the dark matter proponents to modify their models to say how it does behave.
As I understand it, the "behavior" of dark matter in Kroupa's analysis is the behavior that is claimed for it by dark matter proponents. So if dark matter doesn't behave the way dark matter proponents say it does, the burden would be on the dark matter proponents to modify their models to say how it does behave.
Trust me this is a straw man picking at a hole of a yet incomplete theory to claim the whole deck of cards is invalid.
AFAIK none of these alternatives offer a serious explanation of gravitational lensing for instance (yet, I'm happy for someone to make a theoretical breakthrough that explains away the need for an unknown new particle, but that just opens more questions around CP violation and so on)
AFAIK none of these alternatives offer a serious explanation of gravitational lensing for instance (yet, I'm happy for someone to make a theoretical breakthrough that explains away the need for an unknown new particle, but that just opens more questions around CP violation and so on)
> Trust me
Why? Who made you an infallible authority?
> none of these alternatives
The basic point I described is not proposing an alternative to dark matter, and I'm not asking for a refutation of Kroupa's well-known preference for alternative gravity theories. I'm just pointing out that Kroupa has described a prediction of the dark matter hypothesis that does not appear to match observations. I'm wondering if any proponent of the dark matter hypothesis has a counter argument to this: either an explanation of why the dark matter hypothesis doesn't make the prediction Kroupa is describing, or an explanation of why that prediction does match observations after all. This seems to me to be a perfectly reasonable question that does not require any discussion of alternative theories at all.
Why? Who made you an infallible authority?
> none of these alternatives
The basic point I described is not proposing an alternative to dark matter, and I'm not asking for a refutation of Kroupa's well-known preference for alternative gravity theories. I'm just pointing out that Kroupa has described a prediction of the dark matter hypothesis that does not appear to match observations. I'm wondering if any proponent of the dark matter hypothesis has a counter argument to this: either an explanation of why the dark matter hypothesis doesn't make the prediction Kroupa is describing, or an explanation of why that prediction does match observations after all. This seems to me to be a perfectly reasonable question that does not require any discussion of alternative theories at all.
> Who made you an infallible authority?
I'm not infallible but I do have a PhD in the study of CPV in particle physics so I understand this at a level enough to pass a doctoral viva.
Alternate gravity theories struggle with gravitational lensing. This is a proven observable optical phenomena in the study of the universe.
Kroupa is still trying to explain the rotational differences between observation and "normal" Newtonian/Einstein gravity. This is colloquially referred to as Dark Matter. A gravitational (matter like) effect, which doesn't interact optically via standard EM as we can see the galaxies and stars. Hence the name Dark Matter.
I'm not infallible but I do have a PhD in the study of CPV in particle physics so I understand this at a level enough to pass a doctoral viva.
Alternate gravity theories struggle with gravitational lensing. This is a proven observable optical phenomena in the study of the universe.
Kroupa is still trying to explain the rotational differences between observation and "normal" Newtonian/Einstein gravity. This is colloquially referred to as Dark Matter. A gravitational (matter like) effect, which doesn't interact optically via standard EM as we can see the galaxies and stars. Hence the name Dark Matter.
> Alternate gravity theories
Are not what I'm asking about here. I know Kroupa pushes them, but that's not the part of Kroupa's work that I'm asking about.
> Kroupa is still trying to explain the rotational differences between observation and "normal" Newtonian/Einstein gravity.
Not in the specific item I'm asking about. In that specific item, he's not talking about any alternative theories of gravity at all. He's pointing out what he claims is a conflict between the predictions of the dark matter hypothesis and actual observations. I've already explained what a counter argument to that would look like. Do you have one?
Are not what I'm asking about here. I know Kroupa pushes them, but that's not the part of Kroupa's work that I'm asking about.
> Kroupa is still trying to explain the rotational differences between observation and "normal" Newtonian/Einstein gravity.
Not in the specific item I'm asking about. In that specific item, he's not talking about any alternative theories of gravity at all. He's pointing out what he claims is a conflict between the predictions of the dark matter hypothesis and actual observations. I've already explained what a counter argument to that would look like. Do you have one?
Unfortunately you are getting a little crossed from your perspective. You're asking a question that to experts is structured oddly because you can't disentangle things you're trying to separate.
I'll try to explain.
Again dark matter is an attempt to explain a collection of observations that don't match current accepted theoretical models.
There "classical dark matter hypothesises" is just that. That these observations can be explained by a quantizable matter candidate of some form with some yet to be determined properties.
The only non particle descriptions of "dark matter phenomena" is a modified gravity framework. These attempt to address the "classical dark matter phenomena" whilst disentangling it from the "CPV phenomena". This is fine but breaks the big bang model at the stage of baryogenesis (matter formation from pure energy).
There is the possibility that you can explain "classical dark matter phenomena" without demanding it also be responsible for CPV. However, if you do that the CPV step of the big bang model demands additional particle candidates which then raises the problem of what do they look like and where are they and do they interact with the Higgs field and therefore have mass.
There are no counter arguments to "classical dark matter phenomena" because they are just that. Observed natural phenomena which do not fit into our current understanding of the universe.
A "complete dark matter theory" tends to explain CPV+DM. These again don't make many testable predictions other than a (potentially TeV scale) weekly interacting particle candidate. So the testable prediction is that a dark matter candidate exists and we can observe it.
> I've already explained what a counter argument to that would look like. Do you have one?
I'll choose to read that in a relaxed manner, albeit it's a bit direct. There is no counter argument to natural phenomena. The main 2 theories are that dark matter particles exist and we can find them or we can't. MOND et al make few predictions and struggle to observe defined "gravitational phenomena", hence why there is little interest in them. There are differences between DM particle models but almost all agree that the major premise is that we might/should be able to see certain particle types given how they interact.
I'll try to explain.
Again dark matter is an attempt to explain a collection of observations that don't match current accepted theoretical models.
There "classical dark matter hypothesises" is just that. That these observations can be explained by a quantizable matter candidate of some form with some yet to be determined properties.
The only non particle descriptions of "dark matter phenomena" is a modified gravity framework. These attempt to address the "classical dark matter phenomena" whilst disentangling it from the "CPV phenomena". This is fine but breaks the big bang model at the stage of baryogenesis (matter formation from pure energy).
There is the possibility that you can explain "classical dark matter phenomena" without demanding it also be responsible for CPV. However, if you do that the CPV step of the big bang model demands additional particle candidates which then raises the problem of what do they look like and where are they and do they interact with the Higgs field and therefore have mass.
There are no counter arguments to "classical dark matter phenomena" because they are just that. Observed natural phenomena which do not fit into our current understanding of the universe.
A "complete dark matter theory" tends to explain CPV+DM. These again don't make many testable predictions other than a (potentially TeV scale) weekly interacting particle candidate. So the testable prediction is that a dark matter candidate exists and we can observe it.
> I've already explained what a counter argument to that would look like. Do you have one?
I'll choose to read that in a relaxed manner, albeit it's a bit direct. There is no counter argument to natural phenomena. The main 2 theories are that dark matter particles exist and we can find them or we can't. MOND et al make few predictions and struggle to observe defined "gravitational phenomena", hence why there is little interest in them. There are differences between DM particle models but almost all agree that the major premise is that we might/should be able to see certain particle types given how they interact.
> You're asking a question that to experts is structured oddly because you can't disentangle things you're trying to separate.
To me this reads as the answer "no" to the question I asked. Nobody actually has a counter argument. "Experts" have simply chosen to dismiss the matter without any argument at all.
To expand on this somewhat: you appear to believe that I am asking for some kind of separation of observations, so that we consider only the particular observations Kroupa refers to (orbits of small satellite galaxies around large galaxies) and ignore all the other observations. That is not what I am asking. I am asking for a simple response from "experts" who support the dark matter hypothesis in general to these two questions:
(1) Is Kroupa correct in his claims about what dark matter models of "halos" around galaxies predict regarding the orbits of small satellite galaxies around larger galaxies? If not, why not?
(2) Is Kroupa correct that actual observations of the orbits of small satellite galaxies around larger galaxies do not match the predictions of dark matter models? If not, why not?
These seem to me like straightforward questions of the kind that scientists pose to other scientists all the time, and it does not seem credible to me that "experts" would not have responses to them along any of several obvious lines:
(A) Kroupa's computations of the predictions of dark matter "halo" models are wrong. Here are the correct predictions, which match observations.
(B) Kroupa's claims about the predictions are correct, but his comparison with the data is wrong. Here is the correct comparison with the data, which shows that the models match observations.
(C) Kroupa's claims that the predictions don't match observations in this particular domain are correct taken in isolation. However, when the entirety of all observations are considered, including ones that have nothing to do with individual galaxies (such as the evolution of the early universe), the dark matter models do much better at minimizing the overall error between model and observation than any of the alternative models, including the ones Kroupa favors.
You seem to be leaning towards something like (C), but if so, you could just say (C) and be done with it. Instead, you appear to be trying to avoid any possible admission that there is any discrepancy between dark matter models and observations at all, which IMO is not a good strategy. No model ever matches 100% of observations.
> dark matter is an attempt to explain a collection of observations that don't match current accepted theoretical models
I would not put it that way. I would put it that dark matter is an attempt to explain a collection of observations using currently accepted theoretical models (General Relativity and the relevant solutions to the Einstein Field Equation), by making use of a free parameter in the models, namely the assumed stress-energy tensor (or distribution of matter, if you like). By adding a "dark matter" component to the distribution of matter, which does not interact electromagnetically and therefore is not visible to us by any means other than its gravitational effects, many observations can be matched much better.
MOND, by contrast, proposes modifying the theory of gravity in general. That, to me, is a much bigger change than adding a component to the distribution of matter.
> There is no counter argument to natural phenomena.
So what? I wasn't asking for a counter argument to "natural phenomena". I was asking for a counter argument to a claim that a particular model makes predictions that don't match observations. Claims like this are made all the time in science, and the appropriate response is to give a counter argument along the lines I described. I have not seen one, and as I noted above, all your remarks have given me the strong impression that there isn't one, and that "experts" have no interest in providing one. That answers my question, although no doubt the inferences I draw from that answer will be very different than yours.
To me this reads as the answer "no" to the question I asked. Nobody actually has a counter argument. "Experts" have simply chosen to dismiss the matter without any argument at all.
To expand on this somewhat: you appear to believe that I am asking for some kind of separation of observations, so that we consider only the particular observations Kroupa refers to (orbits of small satellite galaxies around large galaxies) and ignore all the other observations. That is not what I am asking. I am asking for a simple response from "experts" who support the dark matter hypothesis in general to these two questions:
(1) Is Kroupa correct in his claims about what dark matter models of "halos" around galaxies predict regarding the orbits of small satellite galaxies around larger galaxies? If not, why not?
(2) Is Kroupa correct that actual observations of the orbits of small satellite galaxies around larger galaxies do not match the predictions of dark matter models? If not, why not?
These seem to me like straightforward questions of the kind that scientists pose to other scientists all the time, and it does not seem credible to me that "experts" would not have responses to them along any of several obvious lines:
(A) Kroupa's computations of the predictions of dark matter "halo" models are wrong. Here are the correct predictions, which match observations.
(B) Kroupa's claims about the predictions are correct, but his comparison with the data is wrong. Here is the correct comparison with the data, which shows that the models match observations.
(C) Kroupa's claims that the predictions don't match observations in this particular domain are correct taken in isolation. However, when the entirety of all observations are considered, including ones that have nothing to do with individual galaxies (such as the evolution of the early universe), the dark matter models do much better at minimizing the overall error between model and observation than any of the alternative models, including the ones Kroupa favors.
You seem to be leaning towards something like (C), but if so, you could just say (C) and be done with it. Instead, you appear to be trying to avoid any possible admission that there is any discrepancy between dark matter models and observations at all, which IMO is not a good strategy. No model ever matches 100% of observations.
> dark matter is an attempt to explain a collection of observations that don't match current accepted theoretical models
I would not put it that way. I would put it that dark matter is an attempt to explain a collection of observations using currently accepted theoretical models (General Relativity and the relevant solutions to the Einstein Field Equation), by making use of a free parameter in the models, namely the assumed stress-energy tensor (or distribution of matter, if you like). By adding a "dark matter" component to the distribution of matter, which does not interact electromagnetically and therefore is not visible to us by any means other than its gravitational effects, many observations can be matched much better.
MOND, by contrast, proposes modifying the theory of gravity in general. That, to me, is a much bigger change than adding a component to the distribution of matter.
> There is no counter argument to natural phenomena.
So what? I wasn't asking for a counter argument to "natural phenomena". I was asking for a counter argument to a claim that a particular model makes predictions that don't match observations. Claims like this are made all the time in science, and the appropriate response is to give a counter argument along the lines I described. I have not seen one, and as I noted above, all your remarks have given me the strong impression that there isn't one, and that "experts" have no interest in providing one. That answers my question, although no doubt the inferences I draw from that answer will be very different than yours.
In my opinion, the big bang model, along with all of GR - LCDM is broken and can not be fixed.
Please take a look at the modified gravity proposal that I have put forward. This idea incorporates a mechanism that would explain why gravity might slightly deviate from Newtonian and/or GR in some circumstances.
This paper also adapts GR in such a way that it is consistent with galactic rotation rates, the anisotropies of the CMB, and cosmological expansion -- while showing that the simple operation of gravity is the cause of each of these phenomena.
This idea, Cyclic Gravity and Cosmology (CGC) predicts that there are discrete specific sizes allowable for macro-objects. The instability of Bennu and the fact that it behaves more like loosely held scree rather than a compact mass -- is an example of a mass that is not exactly at one of the discrete allowable sizes. Please also refer to the link I included wherein I uploaded a video simulation of the formation of a solar system using this type of force law. (This is in section 18 of the paper)
I would greatly appreciate any comments on this idea. A copy may be downloaded here:
https://vixra.org/pdf/2203.0032v3.pdf
Please take a look at the modified gravity proposal that I have put forward. This idea incorporates a mechanism that would explain why gravity might slightly deviate from Newtonian and/or GR in some circumstances.
This paper also adapts GR in such a way that it is consistent with galactic rotation rates, the anisotropies of the CMB, and cosmological expansion -- while showing that the simple operation of gravity is the cause of each of these phenomena.
This idea, Cyclic Gravity and Cosmology (CGC) predicts that there are discrete specific sizes allowable for macro-objects. The instability of Bennu and the fact that it behaves more like loosely held scree rather than a compact mass -- is an example of a mass that is not exactly at one of the discrete allowable sizes. Please also refer to the link I included wherein I uploaded a video simulation of the formation of a solar system using this type of force law. (This is in section 18 of the paper)
I would greatly appreciate any comments on this idea. A copy may be downloaded here:
https://vixra.org/pdf/2203.0032v3.pdf
Tl;Dr c is closest to what you're asking but it's more like.
(D) Kroupka is making bold claims that have to be verified first in the scientific arena very loudly and publically. That is odd. He is claiming that DM doesn't exist which is effectively saying the particle solution to the problem can't exist. This breaks the big bang model as we understand it as I've stated. And is offering a gravity based solution which explains some small phenomena which he claims that not only that this isn't modelled accurately currently but that it can't be using the DM models. That claim requires huge effort to correctly simulate the matter field as it _might_ exist and that requires more assumptions. This could mean certain particle solutions are ruled out or that we need to revise the particle model (fantastic we learned something), but it's much less likely that it's completely dead just because one test says so.
His model may be valid. His data might be good. His conclusion has little to do with either.
Just because a theory doesn't match all observations doesn't mean people stop working on it. If that happened the foundations leading to the Higgs scalar boson wouldn't have been researched as at the time everyone was interested in understanding other field theories.
Ok some background.
DM research was introduced as a solution to the problem of the distribution of mass within galaxies. I.e. orbital velocities of stars within a single galaxy.
In order to try and understand this phenomena models were used to simulate the distribution of "matter fields" within galaxies. Now modern modelling has evolved to simulate complex systems of multiple galaxies or even larger. We now suspect and have strong evidence for huge mega structures (MPa mega parsecs in size) made of some "DM goop" in the universe.
Modeling of this is notoriously difficult and relies on numerous assumptions because we can't model everything exactly so we take sensible shortcuts which shouldn't impact the physics of interest for the simulation.
Large simulations have problems the further they evolve. This is a stochastic not model dependent statement. Modelling a thing we're yet to observe is even more difficult.
Most claims that DM can't exist are people modifying gravity in some way to remove DM as a physical particle that you can build a DM hammer out of in principle. These claims are not entirely baseless but really struggle when you try to match large gravitational structures we have seen so far in the universe (cosmic filaments).
Kroupa claiming his simulation has to be the only simulation to explain a problem (if he makes or infers this) would be false. Everything in science has requirement of reproducibility which goes beyond share the source and run the tool.
Kroupa claiming that his model perfectly describes this set of observations might be interesting, but is yet to be demonstrated at different scales. Again this has to satisfy orbital momenta of stars within a galaxy as well as demonstrating larger scale effects such as gravitational lensing.
Dark matter simulations _all of them_ will have some amount of disagreement or uncertainty. That is the nature of scientific computer modelling and comparison to scientificly collected data. Uncertainty and error estimation/understanding is a huge part of this field. Anyone claiming exact results better have a huge amount of data to back it up.
This is either a conversation that would have been easier by Skype. I'm guessing you don't have a strong background in a formal science. I'm not saying this from some pedastle, it's a joint question/observation of you focusing on the socialogical implications and exactness of a thing.
There is no lack of interest from experts to talk about their field. There is almost never a lack of wanting to move away from the "status quo" in the scientific community. Especially in blue sky particle and astro research at a professional level. The public perception of this existing comes from 2 issues. 1) "loud" individuals who shout loudly that they're not being heard will be ignored. That isn't discourse, that is someone acting like a small child within this area. Unfortunately they often get awarded by funding and we're stuck with them. As they get pushed aside for shouting rather than discussing they tend to get louder. 2) the media loves to paint the image of scientists sitting there as gatekeepers to some theoretical framework. This is fun in movies etc but mostly we talk about this in science education as a case of remember the mistakes from the last 100 years. As a result you will be looked at strangely for dismissing an idea out of hand without proof or testability.
(D) Kroupka is making bold claims that have to be verified first in the scientific arena very loudly and publically. That is odd. He is claiming that DM doesn't exist which is effectively saying the particle solution to the problem can't exist. This breaks the big bang model as we understand it as I've stated. And is offering a gravity based solution which explains some small phenomena which he claims that not only that this isn't modelled accurately currently but that it can't be using the DM models. That claim requires huge effort to correctly simulate the matter field as it _might_ exist and that requires more assumptions. This could mean certain particle solutions are ruled out or that we need to revise the particle model (fantastic we learned something), but it's much less likely that it's completely dead just because one test says so.
His model may be valid. His data might be good. His conclusion has little to do with either.
Just because a theory doesn't match all observations doesn't mean people stop working on it. If that happened the foundations leading to the Higgs scalar boson wouldn't have been researched as at the time everyone was interested in understanding other field theories.
Ok some background.
DM research was introduced as a solution to the problem of the distribution of mass within galaxies. I.e. orbital velocities of stars within a single galaxy.
In order to try and understand this phenomena models were used to simulate the distribution of "matter fields" within galaxies. Now modern modelling has evolved to simulate complex systems of multiple galaxies or even larger. We now suspect and have strong evidence for huge mega structures (MPa mega parsecs in size) made of some "DM goop" in the universe.
Modeling of this is notoriously difficult and relies on numerous assumptions because we can't model everything exactly so we take sensible shortcuts which shouldn't impact the physics of interest for the simulation.
Large simulations have problems the further they evolve. This is a stochastic not model dependent statement. Modelling a thing we're yet to observe is even more difficult.
Most claims that DM can't exist are people modifying gravity in some way to remove DM as a physical particle that you can build a DM hammer out of in principle. These claims are not entirely baseless but really struggle when you try to match large gravitational structures we have seen so far in the universe (cosmic filaments).
Kroupa claiming his simulation has to be the only simulation to explain a problem (if he makes or infers this) would be false. Everything in science has requirement of reproducibility which goes beyond share the source and run the tool.
Kroupa claiming that his model perfectly describes this set of observations might be interesting, but is yet to be demonstrated at different scales. Again this has to satisfy orbital momenta of stars within a galaxy as well as demonstrating larger scale effects such as gravitational lensing.
Dark matter simulations _all of them_ will have some amount of disagreement or uncertainty. That is the nature of scientific computer modelling and comparison to scientificly collected data. Uncertainty and error estimation/understanding is a huge part of this field. Anyone claiming exact results better have a huge amount of data to back it up.
This is either a conversation that would have been easier by Skype. I'm guessing you don't have a strong background in a formal science. I'm not saying this from some pedastle, it's a joint question/observation of you focusing on the socialogical implications and exactness of a thing.
There is no lack of interest from experts to talk about their field. There is almost never a lack of wanting to move away from the "status quo" in the scientific community. Especially in blue sky particle and astro research at a professional level. The public perception of this existing comes from 2 issues. 1) "loud" individuals who shout loudly that they're not being heard will be ignored. That isn't discourse, that is someone acting like a small child within this area. Unfortunately they often get awarded by funding and we're stuck with them. As they get pushed aside for shouting rather than discussing they tend to get louder. 2) the media loves to paint the image of scientists sitting there as gatekeepers to some theoretical framework. This is fun in movies etc but mostly we talk about this in science education as a case of remember the mistakes from the last 100 years. As a result you will be looked at strangely for dismissing an idea out of hand without proof or testability.
> (D) Kroupka is making bold claims that have to be verified first in the scientific arena very loudly and publically.
Meaning basically that other experts haven't had time yet to check his work? How long is that expected to take? The paper I referenced was published in 2015.
> He is claiming that DM doesn't exist
Yes, on the basis of his claim that dark matter models make predictions about the orbits of small satellite galaxies around larger galaxies that don't match observations. As I've said, these kinds of claims get made in science all the time. Scientific models are supposed to be tested against observations. When someone sees a mismatch, they're supposed to say so. That's part of how science is supposed to work.
> This breaks the big bang model as we understand it as I've stated.
More precisely, it "breaks" the belief that we can construct a valid model of our universe using standard General Relativity, on the basis of the claim that we cannot find any assumption for the distribution of matter that gives a satisfactory fit against all observations. That's the larger claim he's making and the basis of his advocacy for alternative theories of gravity, yes. But, as I've already stated, that larger claim is not what I have been asking about.
> it's much less likely that it's completely dead just because one test says so.
That doesn't change the fact that there should be some answer to how that one test comes out: either it does come out the way he claims, or it doesn't. Which is all I was asking about. If the answer is "nobody else has had the time or resources to check as yet", then that's the answer.
> Ok some background.
While this is all valid information it's not information I really needed. I'm well aware of the difficulties involved in constructing these models and checking them against observations.
> I'm guessing you don't have a strong background in a formal science.
Your guess would be wrong. I don't currently do scientific research for a living, but that doesn't mean I don't have a lot of background in how science works.
> you focusing on the socialogical implications and exactness of a thing.
I have no idea where you are getting this from. I haven't asked about "sociological implications" at all. You're the one who keeps bringing that up. And I have already explicitly recognized that no scientific model matches observations with 100% exactness.
> The public perception
Has nothing to do with what I've been asking about. I haven't been asking general questions about how the scientific field of cosmology works or whether or not cosmologists are supporting a "status quo" or whether or not "dissenters" in science get a fair hearing. I've been asking a very specific question which I've already described several times.
Meaning basically that other experts haven't had time yet to check his work? How long is that expected to take? The paper I referenced was published in 2015.
> He is claiming that DM doesn't exist
Yes, on the basis of his claim that dark matter models make predictions about the orbits of small satellite galaxies around larger galaxies that don't match observations. As I've said, these kinds of claims get made in science all the time. Scientific models are supposed to be tested against observations. When someone sees a mismatch, they're supposed to say so. That's part of how science is supposed to work.
> This breaks the big bang model as we understand it as I've stated.
More precisely, it "breaks" the belief that we can construct a valid model of our universe using standard General Relativity, on the basis of the claim that we cannot find any assumption for the distribution of matter that gives a satisfactory fit against all observations. That's the larger claim he's making and the basis of his advocacy for alternative theories of gravity, yes. But, as I've already stated, that larger claim is not what I have been asking about.
> it's much less likely that it's completely dead just because one test says so.
That doesn't change the fact that there should be some answer to how that one test comes out: either it does come out the way he claims, or it doesn't. Which is all I was asking about. If the answer is "nobody else has had the time or resources to check as yet", then that's the answer.
> Ok some background.
While this is all valid information it's not information I really needed. I'm well aware of the difficulties involved in constructing these models and checking them against observations.
> I'm guessing you don't have a strong background in a formal science.
Your guess would be wrong. I don't currently do scientific research for a living, but that doesn't mean I don't have a lot of background in how science works.
> you focusing on the socialogical implications and exactness of a thing.
I have no idea where you are getting this from. I haven't asked about "sociological implications" at all. You're the one who keeps bringing that up. And I have already explicitly recognized that no scientific model matches observations with 100% exactness.
> The public perception
Has nothing to do with what I've been asking about. I haven't been asking general questions about how the scientific field of cosmology works or whether or not cosmologists are supporting a "status quo" or whether or not "dissenters" in science get a fair hearing. I've been asking a very specific question which I've already described several times.
Interestingly, a similar argument (ie. “if it exists, it should behave like this, and it doesn’t”) was used to disprove the existence of the aether[1].
1: Michelson-Morley experiment: https://physics.stackexchange.com/a/472611
1: Michelson-Morley experiment: https://physics.stackexchange.com/a/472611
Yes, and it is a very nice experiment.
However, "dark matter" is an admittedly lose framework it could be due to 1 new type of particles, 10, or higher dimensional effects and new physics we don't understand yet. Saying "therefore it doesn't exist" is ignoring the mountain of decades old solid data showing gaps in our knowledge exist.
And as for dark energy... "The universal expansion is accelerating". Well done you now know as much as 99% of the physicists in the world on this strange unexplained problem.
However, "dark matter" is an admittedly lose framework it could be due to 1 new type of particles, 10, or higher dimensional effects and new physics we don't understand yet. Saying "therefore it doesn't exist" is ignoring the mountain of decades old solid data showing gaps in our knowledge exist.
And as for dark energy... "The universal expansion is accelerating". Well done you now know as much as 99% of the physicists in the world on this strange unexplained problem.
We consider particles with oscillatory behaviour sufficiently different from aether to abandon the name and the concept as useless. But contrary to aether, dark matter is still a new, vague and complicated concept: there is ample room to evolve dark matter theories without giving up on the idea of dark matter.
In any case competing theories will need to converge towards new experimental evidence and therefore towards each other, and then names and starting principles will be unimportant.
In any case competing theories will need to converge towards new experimental evidence and therefore towards each other, and then names and starting principles will be unimportant.
Your statement implies dark matter cannot be falsified by a contradicting observation, because it (dark matter) hasn't yet been observed. But if it doesn't exist, then it will never be observed. So it, therefore, can never be falsified?
If I'm straw manning you, it is unintentional. How would you propose dark matter be falsified?
If I'm straw manning you, it is unintentional. How would you propose dark matter be falsified?
Dark matter as a particle has to have certain properties in order to satisfy what we know about a) it's EW interactions and b) the fact we haven't seen it yet.
Over the next 20 years or so we will likely cover a huge amount of the phase space of direct observation of dark matter like candidates assuming they weakly interact with the standard model.
If we observe it, great we now know a huge chunk more than ever before of the universe.
If we fail to observe it then we have to go away and explain the Dark Matter problem another way. Axions are my personal favourite here because I claim nature for her beauty is sometimes horrible. But this could (in the most scary scenario) potentially be non quantisable interactions between unknown aspects of the universe. At that point we need to further our understanding of potential graviton candidates to evolve our theories of spacetime.
DM isn't a solid prediction like an aether it's a statement of a big gap in our knowledge that has implications to asto and particle physics models.
The big problem is then CP violation (why more matter than not, real why are we here at all stuff). This can't be explained by the standard model and stuff we can see and touch as far as we know. So we assume that this huge amount of it that we can't explain must come from interactions with new particles somewhere in some way at some energy scale.
Physicists try to narrow down that phase space of where and how but a lot of this stuff makes the search for the higgs, look like cheating and watching where your parents hid the Easter eggs. There is scary little to directly go on so theoreticians have to get clever.
Edit: There is also little to say that extra-SM CP violation _must_ be from the same source as Dark Matter astro candidates. The combination of the 2 fields is much more a car of. "Hmm we both have a missing piece in our jigsaw that has 3 of the same sides and a 4th we've never seen. That's odd let's look together to try and find it." Modeling of the early universe to today relies on some unknown amount of CP violation occurring and we know we see it in particle physics which describes everything we see eat and touch. So why the amounts are so different (orders of magnitude different) keeps some scientists up at night.
Over the next 20 years or so we will likely cover a huge amount of the phase space of direct observation of dark matter like candidates assuming they weakly interact with the standard model.
If we observe it, great we now know a huge chunk more than ever before of the universe.
If we fail to observe it then we have to go away and explain the Dark Matter problem another way. Axions are my personal favourite here because I claim nature for her beauty is sometimes horrible. But this could (in the most scary scenario) potentially be non quantisable interactions between unknown aspects of the universe. At that point we need to further our understanding of potential graviton candidates to evolve our theories of spacetime.
DM isn't a solid prediction like an aether it's a statement of a big gap in our knowledge that has implications to asto and particle physics models.
The big problem is then CP violation (why more matter than not, real why are we here at all stuff). This can't be explained by the standard model and stuff we can see and touch as far as we know. So we assume that this huge amount of it that we can't explain must come from interactions with new particles somewhere in some way at some energy scale.
Physicists try to narrow down that phase space of where and how but a lot of this stuff makes the search for the higgs, look like cheating and watching where your parents hid the Easter eggs. There is scary little to directly go on so theoreticians have to get clever.
Edit: There is also little to say that extra-SM CP violation _must_ be from the same source as Dark Matter astro candidates. The combination of the 2 fields is much more a car of. "Hmm we both have a missing piece in our jigsaw that has 3 of the same sides and a 4th we've never seen. That's odd let's look together to try and find it." Modeling of the early universe to today relies on some unknown amount of CP violation occurring and we know we see it in particle physics which describes everything we see eat and touch. So why the amounts are so different (orders of magnitude different) keeps some scientists up at night.
The idea is to propose a model that does not need dark matter to describe observations.
Unfortunately a lot of the models try to remove DM completely from either a gravity or CP perspective and both have direct consequences as to what sort of stable structures in the universe that allow to form. And the models often conflict with other observations showing theyre no better.
It's asif Newton observed an extra solar comet and therefore decided the Principia must otherwise all be wrong. It's a big step to say shinny thing in sky makes the Apple not fall as we observe it.
It's asif Newton observed an extra solar comet and therefore decided the Principia must otherwise all be wrong. It's a big step to say shinny thing in sky makes the Apple not fall as we observe it.
We cannot simulate evolution of galaxies using equations of General Relativity. So at best the simulations are done using Newton mechanics with minimal corrections like accounting for finite speed of light. And often it is not even done using Newton mechanics per see, but numerical models use artificial constrains like a minimal distance between stars to avoid dealing with numerical instabilities.
Yet there is no proof that such simplifications or constrains are valid on the scale of a typical galaxy. Moreover, when people managed to use full equations of General Relativity, then it was possible to account the effects previously thought to require the dark matter hypothesis.
So until it is mathematically proven that the current simulations are valid approximations, I will remain very skeptical about the dark matter.
Yet there is no proof that such simplifications or constrains are valid on the scale of a typical galaxy. Moreover, when people managed to use full equations of General Relativity, then it was possible to account the effects previously thought to require the dark matter hypothesis.
So until it is mathematically proven that the current simulations are valid approximations, I will remain very skeptical about the dark matter.
Like the GP, I'm not in love with DM hypothesis and wouldn't mind something else. I also used to think the same as you. But DM explains a lot of disparate effects, in ways that MOND does not.
The best-well known effect is the "missing mass" in rotating galaxies. Well recently we found galaxies that look like they have no dark matter in them - i.e. they behave as you would expect from classical gravity/centripetal force arguments [1]. So while you can tweak General Relativity to match some of the effects in typical galaxies, you would then expect the results to hold in all galaxies. The "outliers" are easily explained by Dark Matter - they just don't have it for whatever reason.
The simulations of Universe formation, sure have their limitations, but look much worse without DM.
Galaxy clusters look like they have unexplained mass in them. Crucially, this isn't only from observing their rotational speeds (so like galaxy rotations) but also from looking at the strength of gravitational lensing they induce. This is as compared to fluid-dynamics-y calculations of gas temperature, pressure etc.
Bullet cluster is another interesting case [2]. It is the result of a collision of two galaxies. In such cases, you expect (a) the stars to "fly through" each other, as they are basically point masses and only interact gravitationally, but (b) the gasses and dust to collide. In this case, most of the mass is in fact gas and dust, so it should be distributed in the middle of the cluster (having just had an inelastic collision). But in fact observed mass is where the stars are, further out of what looks like center of mass.
[1] https://www.nature.com/articles/d41586-022-01410-x [2] https://en.wikipedia.org/wiki/Bullet_Cluster
The best-well known effect is the "missing mass" in rotating galaxies. Well recently we found galaxies that look like they have no dark matter in them - i.e. they behave as you would expect from classical gravity/centripetal force arguments [1]. So while you can tweak General Relativity to match some of the effects in typical galaxies, you would then expect the results to hold in all galaxies. The "outliers" are easily explained by Dark Matter - they just don't have it for whatever reason.
The simulations of Universe formation, sure have their limitations, but look much worse without DM.
Galaxy clusters look like they have unexplained mass in them. Crucially, this isn't only from observing their rotational speeds (so like galaxy rotations) but also from looking at the strength of gravitational lensing they induce. This is as compared to fluid-dynamics-y calculations of gas temperature, pressure etc.
Bullet cluster is another interesting case [2]. It is the result of a collision of two galaxies. In such cases, you expect (a) the stars to "fly through" each other, as they are basically point masses and only interact gravitationally, but (b) the gasses and dust to collide. In this case, most of the mass is in fact gas and dust, so it should be distributed in the middle of the cluster (having just had an inelastic collision). But in fact observed mass is where the stars are, further out of what looks like center of mass.
[1] https://www.nature.com/articles/d41586-022-01410-x [2] https://en.wikipedia.org/wiki/Bullet_Cluster
The point is that there is no need to tweak GR. For example, [1] shows how properly accounting for GR and using rather detailed data about Milky Way allows to explain the rotational curves.
But GR is complex enough to allow very different behavior depending on the initial conditions of galaxy formations. So it would not be surprising to see different scale of deviations from Newtonian mechanics depending on Galaxy history or age.
[1] - https://arxiv.org/abs/1810.04445
But GR is complex enough to allow very different behavior depending on the initial conditions of galaxy formations. So it would not be surprising to see different scale of deviations from Newtonian mechanics depending on Galaxy history or age.
[1] - https://arxiv.org/abs/1810.04445
One more thing. It is not true that stars simply fly through. Already in the second-order approximation in GR there are forces that behave like Lorentz force of electromagnetism perpendicular to the line of movement. Granted this a small effect, but on the scale of millions of years it matters. That alone can explain a lot of subtle behavior.
I don't understand this: "Without such theory, claiming DM doesn't exist is simply stupid IMO."
You are saying that without another theory to explain something, the current theory must be true because ... How does this logic work exactly?
In the middle ages, there wasn't a theory that explained headaches, so dismissing the idea that we should cut hole in people's skulls to let out the evil spirits is "stupid"?
Dismissing the idea that lighting is caused by Zeus being angry is "stupid" because there is no other theory yet?
You are saying that without another theory to explain something, the current theory must be true because ... How does this logic work exactly?
In the middle ages, there wasn't a theory that explained headaches, so dismissing the idea that we should cut hole in people's skulls to let out the evil spirits is "stupid"?
Dismissing the idea that lighting is caused by Zeus being angry is "stupid" because there is no other theory yet?
Theories are not necessarily absolutely true. They are models that describe and help us understand problems. In most (all?) cases they are approximations. We know that there are problems with them but they are the best tool we have to understand something. Until another tool comes along that works better, the current tool will sufficient.
We know that General Relativity is incomplete. It cannot describe the work at high energies or very small scales. It is useful as far as it goes but it is not a perfect match.
Quantum Mechanics does describe the world of the small and the hot, but we cannot apply it to the larger world. QD, too, is incomplete. We look for a new theory that can combine the features of both but it evades us, so far.
Dark Matter is a similar theory. It describes a world. It seems to describe this work better than other theories like MOND. Looking for actual dark matter will let us see if DM is a good enough theory or not. If another theory can be found that is a better match, we can switch to that. In the meantime, every time we continue to try to verify/disprove DM.
We know that General Relativity is incomplete. It cannot describe the work at high energies or very small scales. It is useful as far as it goes but it is not a perfect match.
Quantum Mechanics does describe the world of the small and the hot, but we cannot apply it to the larger world. QD, too, is incomplete. We look for a new theory that can combine the features of both but it evades us, so far.
Dark Matter is a similar theory. It describes a world. It seems to describe this work better than other theories like MOND. Looking for actual dark matter will let us see if DM is a good enough theory or not. If another theory can be found that is a better match, we can switch to that. In the meantime, every time we continue to try to verify/disprove DM.
We've been looking for dark matter for a long time without success. Until we actually find it, I think it is premature to dismiss out of hand other theories that explain the same phenomena. I'm not sure MOND is any better than DM, but I think it is worth at least pursuing the idea that maybe DM doesn't exist and there is something about gravity that isn't fully explained by general relativity.
> Until we actually find it, I think it is premature to dismiss out of hand other theories that explain the same phenomena. I'm not sure MOND is any better than DM, but I think it is worth at least pursuing the idea
“Dark matter” is just a phenomenological name to whatever mechanism that might explain all the observations consistently. Under this banner, people have studied models of everything from axions to small black holes. Speaking as someone who’s worked in the field, nobody is “ignoring” alternatives to dark matter — if they could think of ways to make up new alternatives (leveraging MOND, or otherwise) they totally would do it — the problem is that most such alternatives raise more complicated questions like breaking the consistency our theory of gravity, or introducing bizarre quantum behavior of certain cosmological fields, etc. Maybe all those problems can also be solved — but nobody knows how! That’s why it appears like they “ignore” it.
Further, any new theory going to supplant dark matter needs to explain not just galactic rotation curves, but also beat the Lambda CDM model in its ability to model/predict details of the cosmic microwave background radiation. AFAIK, MOND or whatever else is not even close, when you try to put all that together.
“Dark matter” is just a phenomenological name to whatever mechanism that might explain all the observations consistently. Under this banner, people have studied models of everything from axions to small black holes. Speaking as someone who’s worked in the field, nobody is “ignoring” alternatives to dark matter — if they could think of ways to make up new alternatives (leveraging MOND, or otherwise) they totally would do it — the problem is that most such alternatives raise more complicated questions like breaking the consistency our theory of gravity, or introducing bizarre quantum behavior of certain cosmological fields, etc. Maybe all those problems can also be solved — but nobody knows how! That’s why it appears like they “ignore” it.
Further, any new theory going to supplant dark matter needs to explain not just galactic rotation curves, but also beat the Lambda CDM model in its ability to model/predict details of the cosmic microwave background radiation. AFAIK, MOND or whatever else is not even close, when you try to put all that together.
> the problem is that most such alternatives raise more complicated questions like breaking the consistency our theory of gravity, or introducing bizarre quantum behavior of certain cosmological fields, etc. Maybe all those problems can also be solved — but nobody knows how! That’s why it appears like they “ignore” it.
To me as a lay-man, this seems like you are indeed ignoring non-dark matter solutions, as dark matter allows you to add various magical elements to explain up whatever is missing in other models. This seems very un-scientific.
To me as a lay-man, this seems like you are indeed ignoring non-dark matter solutions, as dark matter allows you to add various magical elements to explain up whatever is missing in other models. This seems very un-scientific.
> dark matter allows you to add various magical elements to explain up whatever is missing in other models.
It’s not like physicists are looking for every little possibility to be fanciful. Here’s the irony — The “DAMA” experiment has been claiming to have discovered dark matter particles for years, but most physicists don’t trust that the experiment is understood well enough to call it a victory. The process of “adding particles” is an extremely rigorous one (the various detailed checks and stringent requirements involved are unsexy content ignored by pop science). Adding particles is how we discovered the Higgs boson, the weak nuclear force carriers and the internal structure of the proton. It is a battle tested process that underpins the tremendous success of particle physics in the twentieth century.
> To me as a lay-man, this seems like you are indeed ignoring non-dark matter solutions
Seems like there is a massive disconnect with how one actually “does research”. Let’s say I completely agree with you and want to come up with alternative models, and I’ve read the literature — but don’t know how to solve the hairy outstanding problems. What do I actually do when I get up and go to work tomorrow morning? :-P
It’s not like physicists are looking for every little possibility to be fanciful. Here’s the irony — The “DAMA” experiment has been claiming to have discovered dark matter particles for years, but most physicists don’t trust that the experiment is understood well enough to call it a victory. The process of “adding particles” is an extremely rigorous one (the various detailed checks and stringent requirements involved are unsexy content ignored by pop science). Adding particles is how we discovered the Higgs boson, the weak nuclear force carriers and the internal structure of the proton. It is a battle tested process that underpins the tremendous success of particle physics in the twentieth century.
> To me as a lay-man, this seems like you are indeed ignoring non-dark matter solutions
Seems like there is a massive disconnect with how one actually “does research”. Let’s say I completely agree with you and want to come up with alternative models, and I’ve read the literature — but don’t know how to solve the hairy outstanding problems. What do I actually do when I get up and go to work tomorrow morning? :-P
To me as a lay-man, it is unclear what you expect them to do instead. Which part of "nobody has come up with a theory that explains nearly as much as DM can explain" constitutes "ignoring"?
>but I think it is worth at least pursuing the idea that maybe DM doesn't exist and there is something about gravity that isn't fully explained by general relativity.
I don't think anyone is disagreeing with this. However, the current observations are best explained by dark matter. The various MOND models don't fit as well. We either actually detect and confirm dark matter or someone comes up with a MOND model that fits as well or better and has testable predictions.
When people deride MOND, it's not to say that it can't be an answer later but people who are pushing it now are all ignoring some gaping hole in their theory.
Continuing research is fine but, confidence wise, dark matter is in the lead by a lot.
I don't think anyone is disagreeing with this. However, the current observations are best explained by dark matter. The various MOND models don't fit as well. We either actually detect and confirm dark matter or someone comes up with a MOND model that fits as well or better and has testable predictions.
When people deride MOND, it's not to say that it can't be an answer later but people who are pushing it now are all ignoring some gaping hole in their theory.
Continuing research is fine but, confidence wise, dark matter is in the lead by a lot.
It's easy seem like youre in the lead when you have one free parameter for every galaxy.
Dark matter ratios are not free parameters, because galaxies did not form through independent processes. The evidence for a highly homogeneous early universe is overwhelming, and any dark matter candidate that required large-scale inhomogeneity would be rejected out of hand.
If they aren't free parameters then why do we assign arbitrary dark matter content and distribution to galaxies like the bullet cluster/ultradiffuse galaxies with "too much/almost no/no DM" to "make it work out"?
If dark matter distribution weren't arbitrarily assignable, why would reputable physicists suggest that some galaxies might have a dark matter clump at the center and not a supermassive black hole?
The evidence for a highly homogeneous early universe has basically been refuted, unless systematic difficulties in assigning galaxy distances (certainly a possibility) JWST is observing galaxies that are forming WAY too early for a standard gravitational model; MOND has predicted early galaxy formation for more than a decade now.
If dark matter distribution weren't arbitrarily assignable, why would reputable physicists suggest that some galaxies might have a dark matter clump at the center and not a supermassive black hole?
The evidence for a highly homogeneous early universe has basically been refuted, unless systematic difficulties in assigning galaxy distances (certainly a possibility) JWST is observing galaxies that are forming WAY too early for a standard gravitational model; MOND has predicted early galaxy formation for more than a decade now.
> If they aren't free parameters then why do we assign arbitrary dark matter content and distribution to galaxies like the bullet cluster/ultradiffuse galaxies with "too much/almost no/no DM" to "make it work out"?
Something has to explain why galaxies aren't all exactly the same right? Whatever other theory out there will have some "free parameters" that explain that difference won't they? The observable matter differs, why shouldn't dark matter?
I think you're being really cynical about the scientific process here. The process is a new observation comes along that's a bit out of line with the norm and scientists look at the parameters and see if Dark Matter is still a candidate to explain it. Do you think it's unrealistic to assume that different galaxies might have different amounts of dark matter (should it exist)? They have different amounts of observable matter. If there was some galaxy that just didn't make sense by just adding some arbitrary amount of dark matter, it'd put a real damper on the theory but that hasn't happened yet. As of today, the only thing that seems "off" about galaxies is the amount of gravity which is very simply explained by adding in some amount dark matter.
I think my intuition of that is probably the same as your, that it seems kind of ridiculous to just add some invisible matter to the equation but it does actually do a really good job of explaining a few different phenomenon. I suspect the process for the acceptance of dark matter initially began as a "these galaxies are behaving _as if_ they had more matter" and a lot of people trying to explain why that might be to no avail until they kind of just accepted that maybe there just _is_ more matter that we don't see. At least that's how it's been for me. I'm still holding out some kind of hope/expectation that there's a better theory out there that actually explains dark matter/energy in a more satisfactory way.
Something has to explain why galaxies aren't all exactly the same right? Whatever other theory out there will have some "free parameters" that explain that difference won't they? The observable matter differs, why shouldn't dark matter?
I think you're being really cynical about the scientific process here. The process is a new observation comes along that's a bit out of line with the norm and scientists look at the parameters and see if Dark Matter is still a candidate to explain it. Do you think it's unrealistic to assume that different galaxies might have different amounts of dark matter (should it exist)? They have different amounts of observable matter. If there was some galaxy that just didn't make sense by just adding some arbitrary amount of dark matter, it'd put a real damper on the theory but that hasn't happened yet. As of today, the only thing that seems "off" about galaxies is the amount of gravity which is very simply explained by adding in some amount dark matter.
I think my intuition of that is probably the same as your, that it seems kind of ridiculous to just add some invisible matter to the equation but it does actually do a really good job of explaining a few different phenomenon. I suspect the process for the acceptance of dark matter initially began as a "these galaxies are behaving _as if_ they had more matter" and a lot of people trying to explain why that might be to no avail until they kind of just accepted that maybe there just _is_ more matter that we don't see. At least that's how it's been for me. I'm still holding out some kind of hope/expectation that there's a better theory out there that actually explains dark matter/energy in a more satisfactory way.
It's not rediculous to add invisible matter. This is how we discovered Neptune, and Uranus. But it didn't work for Vulcan and Pluto was super sketchy. But to scientist's credit they gave up on dark matter Vulcan when nothing was found, over and over again, and GR explained mercury's orbit.
The analogy would be if we didn't figure out GR, used dark matter to explain mercury's precession, then used dark matter to explain aberrant voyager probe kinetics, then rejected GR because "it failed to explain the weird motion of voyager"
Adding invisible matter is not crazy, but over time you make your model increasingly unfalsifiable as the observations fail to meet the expectations. Ideally that would decrease confidence in the model, but for dark matter it seems to have entrenched the conviction of mainstream astro.
The analogy would be if we didn't figure out GR, used dark matter to explain mercury's precession, then used dark matter to explain aberrant voyager probe kinetics, then rejected GR because "it failed to explain the weird motion of voyager"
Adding invisible matter is not crazy, but over time you make your model increasingly unfalsifiable as the observations fail to meet the expectations. Ideally that would decrease confidence in the model, but for dark matter it seems to have entrenched the conviction of mainstream astro.
The theories you mention (other than Dark Matter) actually have experimental evidence to support them. They are in a completely different league.
I mean MOND has made "surprising predictions that have come true". Here's one that seems very relevant: https://tritonstation.com/2022/01/03/what-jwst-will-see/
Hasn't MOND been disproven by observed existance of galaxy without dark matter?
No? Those galaxies are ultradiffuse galaxies and if their distance estimates are off by about 25%, which is reasonable -- we don't have good models for distances to such cosmic entities -- then the calculation for their rotations bring them in line with expected.
> You are saying that without another theory to explain something, the current theory must be true because ...
Change that "must" to a "may" and you have something that matches what was written in GP.
Change that "must" to a "may" and you have something that matches what was written in GP.
People were being a bit stupid when they dogmatically stuck with the idea that "the earth is the center of the universe" and had to come up with ridiculously complex epicycles and systems of motion to describe the movement of the planets, when really if they had just change their assumptions and frame of reference, it was quite simple to see the planets were orbiting around the sun rather than in some weird epicycle involving the earth.
The impression a lot of people have about dark matter is I think similar -- dark matter / dark energy basically comes up as an explanation for why theory doesn't match what we observe. Thus a lot of people assume there is simply a more reasonable explanation, like a hidden variable we haven't considered, that would result in a theory that matches our observations. When I was in high school physics this was my assumption as well. I think if that were really the problem, though, someone would have solved it by now. That said, never underestimate an entire school of thought's inability to see things differently.
The impression a lot of people have about dark matter is I think similar -- dark matter / dark energy basically comes up as an explanation for why theory doesn't match what we observe. Thus a lot of people assume there is simply a more reasonable explanation, like a hidden variable we haven't considered, that would result in a theory that matches our observations. When I was in high school physics this was my assumption as well. I think if that were really the problem, though, someone would have solved it by now. That said, never underestimate an entire school of thought's inability to see things differently.
Because of this (from the article):
> (b) We need to scientifically understand why the dark-matter based model, being the most falsified physical theory in the history of humankind, continues to be religiously believed to be true by the vast majority of the modern, highly-educated scientists. This is a problem for the sociological and philosophical sciences and suggests a breakdown of the scientific method [18].
There are few hot takes I agree with more. I don't care if the opponents of DM/DE are proponents of MOND, or proponents of something else involving pixies and turtles. We should continue to investigate DM/DE, but not with the religious fervor that we do today.
> (b) We need to scientifically understand why the dark-matter based model, being the most falsified physical theory in the history of humankind, continues to be religiously believed to be true by the vast majority of the modern, highly-educated scientists. This is a problem for the sociological and philosophical sciences and suggests a breakdown of the scientific method [18].
There are few hot takes I agree with more. I don't care if the opponents of DM/DE are proponents of MOND, or proponents of something else involving pixies and turtles. We should continue to investigate DM/DE, but not with the religious fervor that we do today.
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There are no true theories, only theories that agree with observations and allow useful predictions.
> Dismissing the idea that lighting is caused by Zeus being angry is "stupid" because there is no other theory yet?
It's not true that there are no other theories; here in Norway we believe that it's caused by Thor hammering away up there. Some say he's hammering away at dark matter...
It's not true that there are no other theories; here in Norway we believe that it's caused by Thor hammering away up there. Some say he's hammering away at dark matter...
> In the middle ages, there wasn't a theory that explained headaches, so dismissing the idea that we should cut hole in people's skulls to let out the evil spirits is "stupid"?
> Dismissing the idea that lighting is caused by Zeus being angry is "stupid" because there is no other theory yet?
I think you could have picked far better examples.
> Dismissing the idea that lighting is caused by Zeus being angry is "stupid" because there is no other theory yet?
I think you could have picked far better examples.
My general relativity professor claimed the need to postulate the existence of dark matter disappears when using basis vectors for derivations. To be honest, as the only undergraduate in the class, it was mostly way over my head.
Hopefully I'm not misrepresenting his views, I think the paper is DOI:10.1140/epjp/i2011-11032-x
Hopefully I'm not misrepresenting his views, I think the paper is DOI:10.1140/epjp/i2011-11032-x
Clickable: Goedecke - Global embedding via coordinate basis vectors; http://doi.org/10.1140/epjp/i2011-11032-x. I am skeptical of the idea that the need for dark matter can be "conventioned away", but, while I am a mathematician, I'm not even glancingly familiar with the physics.
I don't have access to the paper right now, but the abstract is off to a very bad start.
> any curved Riemannian space must be a subspace of a larger flat host space
This is not even wrong. Yes, you can always embed a Riemannian manifold in a Euclidean space. In fact, there are infinitely many ways to do so. But this is extra structure that you can choose to impose, if you want to - it's not intrinsic.
You might as well say that every string must be a substring of a larger "host" string.
> the 4D Riemann-Christoffel curvature tensor is identically equal to a geometrical tensor associated with the complementary subspace of the host space
Impossibly vague. Yes, sometimes things are equal to other things. What tensor, and associated how?
> Einstein’s field equations are automatically geometrized, with the stress-energy tensor expressed in terms of the contracted complementary tensor
This is a tautology. The Einstein field equations relate the Ricci tensor to the metric and the stress energy tensor, and the Ricci tensor is a contraction of the Riemann curvature tensor. This remains true even if you rename the Riemann curvature tensor "the complementary tensor".
But the deeper problem is this: the entire point of general relativity is that physics does not, in fact, care what coordinates we use. And this is built into the mathematical structure of the theory - there can't be any such thing as the "the coordinate basis vector approach to tensor calculus", because tensors (properly speaking: tensor fields) are, by definition, coordinate-independent objects.
> any curved Riemannian space must be a subspace of a larger flat host space
This is not even wrong. Yes, you can always embed a Riemannian manifold in a Euclidean space. In fact, there are infinitely many ways to do so. But this is extra structure that you can choose to impose, if you want to - it's not intrinsic.
You might as well say that every string must be a substring of a larger "host" string.
> the 4D Riemann-Christoffel curvature tensor is identically equal to a geometrical tensor associated with the complementary subspace of the host space
Impossibly vague. Yes, sometimes things are equal to other things. What tensor, and associated how?
> Einstein’s field equations are automatically geometrized, with the stress-energy tensor expressed in terms of the contracted complementary tensor
This is a tautology. The Einstein field equations relate the Ricci tensor to the metric and the stress energy tensor, and the Ricci tensor is a contraction of the Riemann curvature tensor. This remains true even if you rename the Riemann curvature tensor "the complementary tensor".
But the deeper problem is this: the entire point of general relativity is that physics does not, in fact, care what coordinates we use. And this is built into the mathematical structure of the theory - there can't be any such thing as the "the coordinate basis vector approach to tensor calculus", because tensors (properly speaking: tensor fields) are, by definition, coordinate-independent objects.
Sounds like a misunderstanding, I’d recommend reading the paper before jumping to conclusions. Certainly we covered the various tensors mentioned here in the class I took - if you want details, you have to read past the summary.
General Relativity largely describes how geometry is nature - what may seem obvious from a mathematical perspective isn’t always so from a physical one. The results of using basis vectors for derivations aren’t riddled with artifacts of any particular coordinate system, as it would become immediately clear when expressing Christoffel symbols, for example - they wouldn’t be equal with other approaches.
One of the other students who was getting her PhD specializing in GR said that using a vector approach gave her intuition about concepts she had previously considered incomprehensible.
General Relativity largely describes how geometry is nature - what may seem obvious from a mathematical perspective isn’t always so from a physical one. The results of using basis vectors for derivations aren’t riddled with artifacts of any particular coordinate system, as it would become immediately clear when expressing Christoffel symbols, for example - they wouldn’t be equal with other approaches.
One of the other students who was getting her PhD specializing in GR said that using a vector approach gave her intuition about concepts she had previously considered incomprehensible.
> The results of using basis vectors for derivations aren’t riddled with artifacts of any particular coordinate system, as it would become immediately clear when expressing Christoffel symbols, for example - they wouldn’t be equal with other approaches.
But the Christoffel symbols are artifacts of a particular coordinate system - the real object is the connection, of which the Christoffel symbols are just basis-dependent components.
But the Christoffel symbols are artifacts of a particular coordinate system - the real object is the connection, of which the Christoffel symbols are just basis-dependent components.
I must admit I haven’t touched the subject for twelve years. It sounds like you have a vested interest in dark matter. I think you’d have better luck talking to the author or reading the paper.
The arguments against it sounded plausible at the time.
The arguments against it sounded plausible at the time.
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This Pavel Kroupa guy is popping up a lot across the futurist and credulous science fandom forums. To cut to the chase, his theory only applies to galactic dynamics and it doesn't even do a very good job at it. There are many other aspects that MOND doesn't address. Kroupa doesn't even bring interesting critiques of DM to the table, just claims about his theories and then concluding DM doesn't exist.
> To cut to the chase, his theory only applies to galactic dynamics and it doesn't even do a very good job at it. There are many other aspects that MOND doesn't address.
There are many more that DM doesn't address, or only addressed by extending it with parameters to fine-tune the result, a process which can also be done with MOND. I hate to keep posting this, but it's a good thorough review of the evidence for/against both DM and MOND, and DM does not fair as well as you imply:
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
There are many more that DM doesn't address, or only addressed by extending it with parameters to fine-tune the result, a process which can also be done with MOND. I hate to keep posting this, but it's a good thorough review of the evidence for/against both DM and MOND, and DM does not fair as well as you imply:
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
I'd love to see some papers from more, shall we say, impactful peer-reviewed journals.
May I get your thoughts on this idea of mine:
We all know the marbles on a rubber sheet experiment. Masses produce "dents" in spacetime that "pull" on other objects.
Couldn't it be that that these dents are balanced out by bulges between the masses, that would additionally "push" smaller masses (like solar systems) towards larger masses (like the centers of galaxies)?
In an experiment it would look like this: the rubber sheet seals the top of a container filled with water. Now if you push down at some point, the increasing water pressure will push up all around that point. If you now added a marble onto that bulge, it would roll down a steeper angle than it would in the normal experiment ... just like if there was extra mass ("dark matter").
Couldn't it be that that these dents are balanced out by bulges between the masses, that would additionally "push" smaller masses (like solar systems) towards larger masses (like the centers of galaxies)?
In an experiment it would look like this: the rubber sheet seals the top of a container filled with water. Now if you push down at some point, the increasing water pressure will push up all around that point. If you now added a marble onto that bulge, it would roll down a steeper angle than it would in the normal experiment ... just like if there was extra mass ("dark matter").
Sabine Hoffensteder had apparently the same intuition as you and set out to develop a theory of dark matter as being anti-gravitating matter. It didn’t work out…
https://backreaction.blogspot.com/2021/11/does-anti-gravity-...
> Because I had this idea that anti-gravitating matter could surround normal galaxies and push in on them. Which would create an additional force that looks much like dark matter. Normally the excess force we observe is believed to be caused by more positive mass inside and around the galaxies. But aren’t those situations very similar? More positive mass inside, or negative mass outside pushing in? And if you remember, the important thing about dark energy is that it has negative pressure. Certainly if you have negative energy you can also get negative pressure somehow.
> So using anti-gravitating matter to explain dark matter and dark energy sounds good at first sight. But at second sight neither of those ideas work. The idea that galaxies would be surrounded by anti-gravitating matter doesn’t work because such an arrangement would be dramatically unstable. Remember the anti-gravitating stuff wants to clump just like normal matter. It wouldn’t enclose galaxies of normal matter, it would just form its own galaxies. So getting anti-gravity to explain dark matter doesn’t work even for galaxies, and that’s leaving aside all the other evidence for dark matter.
She goes into a lot more detail in the video (the blog post is just a transcript), but hearing her describe the thought process is interesting because she spent a lot of time on this theory (I’m assuming after she got her phd), so you’re in good company for coming to this initial conclusion at least :)
https://backreaction.blogspot.com/2021/11/does-anti-gravity-...
> Because I had this idea that anti-gravitating matter could surround normal galaxies and push in on them. Which would create an additional force that looks much like dark matter. Normally the excess force we observe is believed to be caused by more positive mass inside and around the galaxies. But aren’t those situations very similar? More positive mass inside, or negative mass outside pushing in? And if you remember, the important thing about dark energy is that it has negative pressure. Certainly if you have negative energy you can also get negative pressure somehow.
> So using anti-gravitating matter to explain dark matter and dark energy sounds good at first sight. But at second sight neither of those ideas work. The idea that galaxies would be surrounded by anti-gravitating matter doesn’t work because such an arrangement would be dramatically unstable. Remember the anti-gravitating stuff wants to clump just like normal matter. It wouldn’t enclose galaxies of normal matter, it would just form its own galaxies. So getting anti-gravity to explain dark matter doesn’t work even for galaxies, and that’s leaving aside all the other evidence for dark matter.
She goes into a lot more detail in the video (the blog post is just a transcript), but hearing her describe the thought process is interesting because she spent a lot of time on this theory (I’m assuming after she got her phd), so you’re in good company for coming to this initial conclusion at least :)
Thanks.
I don't see what would clump, because it's not negative-mass matter floating between galaxies that I'm suggesting.
Just like entangled particles that are lightyears apart, when you measure the angular momentum of one, you know the other's because of conservation laws and not because of some hidden object nudging the particle the right way either.
Spacetime bulging the other way ("anti-gravity") would simply be a feature of spacetime to conserve some other property. In my example that would be the water pressure that wants to stay constant.
Some commenter below mention that this is like a waterbed. I like that analogy. If you put a large marble on a waterbed, not only will it create a trough, it will also ever so slightly lift everything around it.
Just like entangled particles that are lightyears apart, when you measure the angular momentum of one, you know the other's because of conservation laws and not because of some hidden object nudging the particle the right way either.
Spacetime bulging the other way ("anti-gravity") would simply be a feature of spacetime to conserve some other property. In my example that would be the water pressure that wants to stay constant.
Some commenter below mention that this is like a waterbed. I like that analogy. If you put a large marble on a waterbed, not only will it create a trough, it will also ever so slightly lift everything around it.
Sounds like a waterbed… and there are google hits of other people with the same question! You are not alone.
https://science.slashdot.org/story/20/11/22/1714220/to-expla...
https://science.slashdot.org/story/20/11/22/1714220/to-expla...
Another fun possiblity I remember from Universe in a nutshell, is that Dark matter is gravitation leaking from other branes.
In your analogy rubber sheet analogy, it's about stacking another rubber layer on top of current one.
It has no prediction powers , but it would explain things like why gravity is so weak and why we can't detect it.
In your analogy rubber sheet analogy, it's about stacking another rubber layer on top of current one.
It has no prediction powers , but it would explain things like why gravity is so weak and why we can't detect it.
Analogies are great for explaining versions of complex theories, but they rarely prove or disprove the theory because they aren't a 1:1 mapping to the theory, they're analogous. Similar. But similar is not "is the same"
Has anyone in the MoND world looked into the James Webb observations that seem to contradict our current theories of galaxy formation in the early universe?
ie the observations seem to show more mature structures than predicted, we're finding.
I've been wondering if some MoND / non-DM kind of theory may better explain these new JWST observations.
- I'm not anything close to an astrophysicist, so give me some rope :-)
ie the observations seem to show more mature structures than predicted, we're finding.
I've been wondering if some MoND / non-DM kind of theory may better explain these new JWST observations.
- I'm not anything close to an astrophysicist, so give me some rope :-)
The MOND guys are aware: https://tritonstation.com/2022/07/21/jwst-twitter-bender/
Specifically this paper[0] is mentioned as predicting it
> Remarkably, the data roughly follow the green line, which is an L* galaxy magically put in place at the inconceivably high redshift of z=10. Galaxies seem to have gotten big impossibly early. This is why you see us astronomers flipping our lids at the JWST results. Can’t happen.
> Except that it can, and was predicted[0] to do so by Bob Sanders a quarter century ago: “Objects of galaxy mass are the first virialized objects to form (by z=10) and larger structure develops rapidly.”
0: https://arxiv.org/abs/astro-ph/9710335
Specifically this paper[0] is mentioned as predicting it
> Remarkably, the data roughly follow the green line, which is an L* galaxy magically put in place at the inconceivably high redshift of z=10. Galaxies seem to have gotten big impossibly early. This is why you see us astronomers flipping our lids at the JWST results. Can’t happen.
> Except that it can, and was predicted[0] to do so by Bob Sanders a quarter century ago: “Objects of galaxy mass are the first virialized objects to form (by z=10) and larger structure develops rapidly.”
0: https://arxiv.org/abs/astro-ph/9710335
> Galaxies seem to have gotten big impossibly early.
A MoND-like theory that allows the strength of gravity / inertia to vary over time can explain that. Granted, that sounds farfetched, but then, so does DM. Of course, it's easy to spend money looking for DM, and hard to spend money looking for a better theory of gravity.
A MoND-like theory that allows the strength of gravity / inertia to vary over time can explain that. Granted, that sounds farfetched, but then, so does DM. Of course, it's easy to spend money looking for DM, and hard to spend money looking for a better theory of gravity.
Mond doesn't need that to explain early galaxies. When the matter is sparse gravitational contributions are weak and thus overwhelmingly in the O(1/r) regime and not the O(1/r^2) -- this makes gravity "seem stronger", and so stuff clumps together faster.
I believe 99.99% of new discoveries in astrophysics create more problems for cosmic models than they had before. Pluto shocked the scientific world in 2015 when we got up close photos of what was supposed to be a cold frozen stone, being so small and so far from the sun, but it's still geologically active, something no model could account for at the time, nor since afaik.
This made me dig up an old comment I left 8 months ago regarding JWST predictions
https://news.ycombinator.com/item?id=29488993
> the observations seem to show more mature structures than predicted
Thank you for closing the loop for me! (would you happen to have a source?)
https://news.ycombinator.com/item?id=29488993
> the observations seem to show more mature structures than predicted
Thank you for closing the loop for me! (would you happen to have a source?)
Nice recall! Thanks for posting this.
> Has anyone [in the MoND world] looked into the James Webb observations
Probably. Certainly non-MoND people have:
> so give me some rope
Ok, here's some rope <https://telescoper.wordpress.com/2022/08/10/recalibration-of...>
Telescoper is an anagram of Peter Coles. It's his blog. He's a well known physical cosmologist <https://en.wikipedia.org/wiki/Peter_Coles>.
Adams et al., authors of the preprint linked in that blog entry, are all well-known astronomers. Adams is a research associate and Observational Astronomer at <https://en.wikipedia.org/wiki/Jodrell_Bank_Observatory> specializing in high-redshift galaxies, and is in several large-telescope international collaborations (ESO, SKA, MIGHTEE, LADUMA).
The punchline: those seemingly super-far-away galaxies are getting much much closer as JWST's calibrations proceed according to plan.
Probably. Certainly non-MoND people have:
> so give me some rope
Ok, here's some rope <https://telescoper.wordpress.com/2022/08/10/recalibration-of...>
Telescoper is an anagram of Peter Coles. It's his blog. He's a well known physical cosmologist <https://en.wikipedia.org/wiki/Peter_Coles>.
Adams et al., authors of the preprint linked in that blog entry, are all well-known astronomers. Adams is a research associate and Observational Astronomer at <https://en.wikipedia.org/wiki/Jodrell_Bank_Observatory> specializing in high-redshift galaxies, and is in several large-telescope international collaborations (ESO, SKA, MIGHTEE, LADUMA).
The punchline: those seemingly super-far-away galaxies are getting much much closer as JWST's calibrations proceed according to plan.
I would like to toss my own idea into this discussion. This idea incorporates a mechanism that would explain why gravity might slightly deviate from Newtonian and/or GR in some circumstances.
This paper also adapts GR in such a way that it is consistent with galactic rotation rates, the anisotropies of the CMB, and cosmological expansion -- while showing that the simple operation of gravity is the cause of each of these phenomena.
Cyclic Gravity and Cosmology (CGC) predicts that there are discrete specific sizes allowable for macro-objects. The instability of Bennu and the fact that it behaves more like loosely held scree rather than a compact mass -- is an example of a mass that is not exactly at one of the discrete allowable sizes. Please also refer to the link I included wherein I uploaded a video simulation of the formation of a solar system using this type of force law. (This is in section 18 of the paper)
I would greatly appreciate any comments on this idea. Copies may be downloaded here:
https://vixra.org/pdf/2203.0032v3.pdf
This paper also adapts GR in such a way that it is consistent with galactic rotation rates, the anisotropies of the CMB, and cosmological expansion -- while showing that the simple operation of gravity is the cause of each of these phenomena.
Cyclic Gravity and Cosmology (CGC) predicts that there are discrete specific sizes allowable for macro-objects. The instability of Bennu and the fact that it behaves more like loosely held scree rather than a compact mass -- is an example of a mass that is not exactly at one of the discrete allowable sizes. Please also refer to the link I included wherein I uploaded a video simulation of the formation of a solar system using this type of force law. (This is in section 18 of the paper)
I would greatly appreciate any comments on this idea. Copies may be downloaded here:
https://vixra.org/pdf/2203.0032v3.pdf
dark matter - the new epicycle?
I have personally no problems with epicycles. Those were effectively the Fourier decompositions of the elliptical orbits while viewed from the Earth. At some point we found a simpler and a more predictive theory and that naturally produces the right shapes (kepler laws + classical gravitational dynamics) and we choose that instead.
I think many people would be happy (myself included) if there is theory that wouldn't require dark matter and dark energy. But at the moment there is none and to me (and many astrophysicsts) the universe with dark matter is the best description we've found so far of what we observe.
I think many people would be happy (myself included) if there is theory that wouldn't require dark matter and dark energy. But at the moment there is none and to me (and many astrophysicsts) the universe with dark matter is the best description we've found so far of what we observe.
from the angle of "explaining observations" a fundamentally incorrect theory can work well. but it breaks down as soon as you interact with the object of the theory in new ways. in epicycles' case that means traveling to a satellite that doesn't orbit the earth. usually the theory is disproven before it kills people, but you know, possibility's there
I don't believe in fundamentally correct theories. All theories have limitations. They work until they do not. Is general relativity fundamentally correct ? I wouldn't call it that (others may disagree), because it doesn't explain quantum effects or very early universe.
So to me theories are just tools that explain what we see and predict the future.
I'm with you - "All models are wrong, but some models are useful".
I do think dark matter is tantalizing because it hints strongly that our model needs a fundamental change in understanding at some other level. It just feels like too much wall paper to be adding to the model in an attempt to cover the holes.
Doesn't mean I find any of the current alternatives more viable then our current models.
I do think dark matter is tantalizing because it hints strongly that our model needs a fundamental change in understanding at some other level. It just feels like too much wall paper to be adding to the model in an attempt to cover the holes.
Doesn't mean I find any of the current alternatives more viable then our current models.
exactly, so when we attempt to put general relativity into practice at the limit of its predictive capability, we may see something is very wrong, then extrapolate a better model, and a few decades later everyone will look back on general relativity as an example of science's ability to carry us away from grossly false beliefs. as with epicycles. and maybe dark matter.
Theories, sure, but knowledge is not confined to theories, i.e. isn’t there positive knowledge, a.k.a. “facts”?
Yes there are facts. I.e. there is a particle called electron, there is a Sun, Cosmic Microwave background, Milky Way galaxy. I'd say those are facts. But I do think the boundary what's a 'fact' vs model/theory dependent statement can be different among different people.
There are theories with super high levels of supporting evidence, so we treat them as true.
This isn't to say that is a bad thing, it is a great thing.
This isn't to say that is a bad thing, it is a great thing.
I treat them as true because they are true. I guess there is more than one definition of truth.
But I think what you mean that you treat some theories as axioms (temporarily, I hope). It's a great aid in thinking but a great source of confusion for newbies as well.
But I think what you mean that you treat some theories as axioms (temporarily, I hope). It's a great aid in thinking but a great source of confusion for newbies as well.
There are absolutely multiple definitions of truth. "1 + 1 = 2" is not true in the sense that "Paris is the capital of France" or "Water boils at 100C" are true.
Outside of mathematics, not really. Special relativity and QM proved that 300 year old "facts" were actually subtly wrong, for example.
I think the OP's point is that we should understand our current models of natural phenomenon to be just that, models. Outside of their predictive capabilities we should remain humble about how much "truth" they contain and be skeptical of their ability to tell us what's "really going on".
Kepler and Newton's models produce better predictions over a long period than Ptolemaic models, which is great. But it's a bit of delusion to think that necessarily means they are analogous to the cosmological mechanisms that produce orbital mechanics.
Kepler and Newton's models produce better predictions over a long period than Ptolemaic models, which is great. But it's a bit of delusion to think that necessarily means they are analogous to the cosmological mechanisms that produce orbital mechanics.
> I think the OP's point is that we should understand our current models of natural phenomenon to be just that, models
this was my point with the initial epicycle comparison
this was my point with the initial epicycle comparison
Or dark matter - the new germ theory of disease. Both introduce a new, hard-to-observe-with-current-technology entity which explains observations better than any other theory we've came up with. MOND doesn't explain structure formations or lower rotational speed galaxies; miasma didn't explain non-airborne illness.
It's incredibly hard to know until we've either observed DM particles or made good alternative hypothesises which also fit the data.
It's incredibly hard to know until we've either observed DM particles or made good alternative hypothesises which also fit the data.
Dark matter sounds suspiciously like aether to non-experts. I’m not saying it is, but do recall that the concept of aether filling the universe was an immensely popular one prior to the turn of the last century, so not too long ago. We don’t believe it any more, it’s hogwash of course.
Aether seemed to be necessary conceptually because the theory of electromagnetism was a theory of waves, and no would could conceive of waves except in some medium, hence aether. Einstein's breakthrough was to show that the concept of aether was not necessary to explain empirical observations about electromagnetism and the speed of light.
Dark matter, on the other hand, is not a conceptual necessity but an empirical one. Whereas aether was something people clung to because they couldn't imagine a world without it, dark matter is something scientists have been forced into even though the world would be more conceptually elegant without it.
Dark matter, on the other hand, is not a conceptual necessity but an empirical one. Whereas aether was something people clung to because they couldn't imagine a world without it, dark matter is something scientists have been forced into even though the world would be more conceptually elegant without it.
The luminiferous ether theory met the basic criteria of being testable and falsifiable, hence the Michaelson-Morley experiment. Isn't that the basic objection to dark matter, that there's nothing in it that's falsifiable?
The reason we teach the Michaelson-Morley experiment in basic Physics classes is because it's a bedrock example of Science functioning correctly. The reason people believed in the ether theory is because in the wake of Maxwell's revolutionary work, there needed to be an explanation of how light propagated that could be reconciled with Newton's mechanics which had been laid out 200 years earlier. In hindsight, we credit Einstein with finding the way out, but in the late 1800's it was in no way obvious that it was going to work out that way.
The reason we teach the Michaelson-Morley experiment in basic Physics classes is because it's a bedrock example of Science functioning correctly. The reason people believed in the ether theory is because in the wake of Maxwell's revolutionary work, there needed to be an explanation of how light propagated that could be reconciled with Newton's mechanics which had been laid out 200 years earlier. In hindsight, we credit Einstein with finding the way out, but in the late 1800's it was in no way obvious that it was going to work out that way.
> Isn't that the basic objection to dark matter, that there's nothing in it that's falsifiable?
I don't think that's case, at least to me it seems that the basic objection is some vague discomfort with the idea, not an issue with the falsifiability. And dark matter is clearly falsifiable, it has already survived many observations.
The CMB power spectrum would look entirely different if there was no dark matter.
Gravitational lensing in certain areas in the sky wouldn't look as strong as it does without dark matter either.
I don't think that's case, at least to me it seems that the basic objection is some vague discomfort with the idea, not an issue with the falsifiability. And dark matter is clearly falsifiable, it has already survived many observations.
The CMB power spectrum would look entirely different if there was no dark matter.
Gravitational lensing in certain areas in the sky wouldn't look as strong as it does without dark matter either.
Until Michaelson-Morley’s landmark experiment, we hadn’t found a way to falsify aether either. Is there physical proof that dark matter is not falsifiable? If not, we still have a bit further to go.
There is always a tension in Physics between physical proof and observability on the one hand, and having the right idea, the right intuition on the other.
Going back to my Einstein example, there were other Physicists who contributed to Relativity (Lorentz, Minkowski, Poincaré, Fitzgerald) but we give Einstein the most credit because he had the right idea, that it's not enough to treat the speed of light as a constant in your math, you actually have to believe the Universe works that way. One of the stories that gets told is the reason Einstein never got a Nobel prize for Relativity is because the Nobel committee just wasn't ready to give it up and credit Einstein with discovering a new, fundamental truth about the Universe.
Another story that gets told is that when Einstein was an undergrad at the ETH in Zurich, Minkowski was one of his professors and he dismissed Einstein for being a "Lazy Dog" because the math never came easy to him. But he looked at how Physics was taught at the time and knew something had to change. And he was right about that.
I'll just leave this here, Feynman explained it better than I ever will.
https://youtu.be/NM-zWTU7X-k
Going back to my Einstein example, there were other Physicists who contributed to Relativity (Lorentz, Minkowski, Poincaré, Fitzgerald) but we give Einstein the most credit because he had the right idea, that it's not enough to treat the speed of light as a constant in your math, you actually have to believe the Universe works that way. One of the stories that gets told is the reason Einstein never got a Nobel prize for Relativity is because the Nobel committee just wasn't ready to give it up and credit Einstein with discovering a new, fundamental truth about the Universe.
Another story that gets told is that when Einstein was an undergrad at the ETH in Zurich, Minkowski was one of his professors and he dismissed Einstein for being a "Lazy Dog" because the math never came easy to him. But he looked at how Physics was taught at the time and knew something had to change. And he was right about that.
I'll just leave this here, Feynman explained it better than I ever will.
https://youtu.be/NM-zWTU7X-k
Dark Matter in totality is hard to disprove (as it's really not one theory, but a rather large set). But large parts of that parameter space is testable, and is tested. See WIMPs for example, where we searched extensively. Have we ruled out everything? No. But we have ruled out many variants, mass and coupling ranges.
Michaelson-Morley didn't falsify aether. At the time, their results were interpreted within the aether framework in terms of compression of the aether yielding the Lorentz transformations.
We still have the aether, we just call it the "electromagnetic field"
We absolutely do not have an aether! Light does not travel through a medium like ripples in water.
The aether makes specific predictions. Like the fact that we're all traveling through it because it is a background medium. These were clearly refuted.
Fields are not aethers. Fields do not have a reference frame.
The aether makes specific predictions. Like the fact that we're all traveling through it because it is a background medium. These were clearly refuted.
Fields are not aethers. Fields do not have a reference frame.
Why wouldn't dark matter be falsifiable?
I mean, i imagine its difficult because we can't really conduct direct experiments, but i don't see any reason that its non-falsifiable.
I mean, i imagine its difficult because we can't really conduct direct experiments, but i don't see any reason that its non-falsifiable.
As non-expert I have always wondered about Dark Matter and particle physics. So just how many MeV do we need? And how much would that cost?
Lots, and more than we can afford, assuming particle colliders could even produce it.
It's popular to look for types of Dark Matter that interact very weakly with forces other than gravity (WIMPs). That's a lot like the joke of the man searching for his keys under a street light even though he dropped them away from the light, because the light is better there. It's perfectly possible that Dark Matter ONLY interacts gravitationally, and so will never be detected by any of the current approaches. Detecting the gravitational force of an elementary particle is ridiculously difficult, well beyond the sensitivity of any current detectors. Even if we could, there would be a huge noise floor from all the normal matter around!
It's popular to look for types of Dark Matter that interact very weakly with forces other than gravity (WIMPs). That's a lot like the joke of the man searching for his keys under a street light even though he dropped them away from the light, because the light is better there. It's perfectly possible that Dark Matter ONLY interacts gravitationally, and so will never be detected by any of the current approaches. Detecting the gravitational force of an elementary particle is ridiculously difficult, well beyond the sensitivity of any current detectors. Even if we could, there would be a huge noise floor from all the normal matter around!
I thought that a purely gravitationally interacting dark matter would not produce the right clumping, i.e. there must be an additional force -- either one of the known ones, or a new one.
True, a pure GIMP alone can't do it. But they could account for most of the observed effects of Dark Matter, meaning we'd be very far from ever detecting any. And an extra force (if one exists) might interact with Dark Matter but not to any detectable degree (or at all) with normal matter, leaving things in about the same position (you'd never produce Dark Matter from colliding normal matter).
germs are provably real, what you're looking for is miasma
Germs are observable _today_, because we have powerful microscopes. For most of its existence, germ theory relied on unobservable entities, and it had to be supported by the fact that the theory fits the data, not through direct observation. Similarly, dark matter is observable in principle, just not with our current technology.
I don't know which aspects you think dark matter shares with miasma. Dark matter fits all the data; miasma doesn't.
I don't know which aspects you think dark matter shares with miasma. Dark matter fits all the data; miasma doesn't.
miasma largely fit the data for a millennium, the same way dark matter largely fits the data. if you believed in germs in the 1600s, which is about where we are now with dark matter, you would have been considered insane, so i get where you're coming from.
the fact that dark matter is widely accepted without proof, and that the current model continues to encounter new anomalies, puts it about on the same level as strings for me—very cool and i hope it's real, but likely to be explained away when we better understand quantum physics and higher dimensions
the fact that dark matter is widely accepted without proof, and that the current model continues to encounter new anomalies, puts it about on the same level as strings for me—very cool and i hope it's real, but likely to be explained away when we better understand quantum physics and higher dimensions
Sorry, but you're just wrong. You can't look at a disease outbreak and explain the transmission among the population with a miasma-based statistical model. In other words, it doesn't fit the data.
And dark matter is not accepted without proof. It fits the data extremely well. That is the proof. It explains many unrelated phenomena and isn't ruled out by anything; just like gravity. The fact that we can explain why things fall down, why the moon orbits around the earth, why the earth orbits around the sun, why stars form, why planets form and a whole bunch of other phenomena with one force is the proof; we haven't seen a gravity particle, but that doesn't matter, because that's not how proof works in science.
It's not about thinking it's cool and hoping it's real either. It's simply the only explanation we have for a whole bunch of stuff, and it's a damn good explanation that's extremely simple.
That's not to say it's necessarily correct. It's just the only explanation we have, and we have no reason to believe it not to be correct.
And dark matter is not accepted without proof. It fits the data extremely well. That is the proof. It explains many unrelated phenomena and isn't ruled out by anything; just like gravity. The fact that we can explain why things fall down, why the moon orbits around the earth, why the earth orbits around the sun, why stars form, why planets form and a whole bunch of other phenomena with one force is the proof; we haven't seen a gravity particle, but that doesn't matter, because that's not how proof works in science.
It's not about thinking it's cool and hoping it's real either. It's simply the only explanation we have for a whole bunch of stuff, and it's a damn good explanation that's extremely simple.
That's not to say it's necessarily correct. It's just the only explanation we have, and we have no reason to believe it not to be correct.
in AD 700 one would absolutely have been able to explain an outbreak with a miasma-based model, and the explanation absolutely would have become consensus among the best and brightest. you can't apply what we know now to what was known at a given point in the past
> we can explain why things fall down
that's pretty new too! and it's not semantically correct, but was considered so for quite a while. this is a pretty good analogy for why i'm skeptical of dark matter
> we can explain why things fall down
that's pretty new too! and it's not semantically correct, but was considered so for quite a while. this is a pretty good analogy for why i'm skeptical of dark matter
> It fits the data extremely well. That is the proof. It explains many unrelated phenomena and isn't ruled out by anything;
Suppose you had six frames of a ball moving in a parabolic trajectory. A sixth order polynomial would fit the data incredibly well, but I don't think you would accept it as a good model for the motion of the ball.
You can't say "it isn't ruled out by anything":
EFE rules out LCDM. Galaxies are redshift >~ 7 rules out LCDM (we now have galaxies at redshift > 13).
Suppose you had six frames of a ball moving in a parabolic trajectory. A sixth order polynomial would fit the data incredibly well, but I don't think you would accept it as a good model for the motion of the ball.
You can't say "it isn't ruled out by anything":
EFE rules out LCDM. Galaxies are redshift >~ 7 rules out LCDM (we now have galaxies at redshift > 13).
They weren't provably real when proposed.
> Both introduce a new, hard-to-observe-with-current-technology entity which explains observations better than any other theory we've came up with. MOND doesn't explain structure formations or lower rotational speed galaxies
DM's failures are more numerous, and it has to be extended with new assumptions to account for other observations. MOND's predictions fair better as favourable evidence actually [1].
[1] From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
DM's failures are more numerous, and it has to be extended with new assumptions to account for other observations. MOND's predictions fair better as favourable evidence actually [1].
[1] From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
Epicycles aren't wrong. In fact, the Copernican model of the solar system is less correct than the Ptolemaic epicycle model that was being used because Copernicus still viewed orbits as circular.
More to the point, since epicycles are just a Fourier decomposition, they're actually perfectly correct. The problem, though, is that they are a nightmare to compute with unless you have a modern computer.
Once Kepler decided to use an ellipse to model solar orbits; however, things were vastly easier to compute. At that point, the epicycle model got swiftly pushed aside.
More to the point, since epicycles are just a Fourier decomposition, they're actually perfectly correct. The problem, though, is that they are a nightmare to compute with unless you have a modern computer.
Once Kepler decided to use an ellipse to model solar orbits; however, things were vastly easier to compute. At that point, the epicycle model got swiftly pushed aside.
Epicycles aren't wrong, they're not even wrong. You could model an orbit that looks like homer Simpson's face with epicycles, but the ancients weren't sophisticated enough to understand that. The problem is that the technique of epicycles this has diminishing explanatory power, as you add more free variables (how many epicycles you are "allowed" to have.
The reason why LCDM gets called epicycles is that there is charitably one free parameter per galaxy (dm: bm ratio -- but actually more, because it's an arbitrary distribution)... So the fact that it has high explanatory power is unsurprising. And what's should be dismaying is the number of things it can't explain, given just how many free parameters you're allowed to have in a DM model.
The reason why LCDM gets called epicycles is that there is charitably one free parameter per galaxy (dm: bm ratio -- but actually more, because it's an arbitrary distribution)... So the fact that it has high explanatory power is unsurprising. And what's should be dismaying is the number of things it can't explain, given just how many free parameters you're allowed to have in a DM model.
Not a physicist, but it feels more like the orbit of Mercury. Newtonian physics didn't quite predict it correctly, but it was still the best theory available until relativity came along. That seems to be the thrust of the GP comment: "you got a better idea?"
Forget GR. I got a better idea for the orbit of mercury. A ball of dark matter pulling the planet around. Does this seem silly?
Only if we find a better explanation.
This is a constant bug/feature of human thought. When we try to see beyond the limits of our technology we find it irresistible promote explanations that can't be proved yet. Often these placeholder theories turn out to be complete nonsense (epicycles). Often they are incredibly convincing (Dark Matter), and sometimes they even turn out to be mostly correct - so this process is generally a good thing.
Where we run into trouble is by assigning too much credence (or too little skepticism) for that which has not been proven yet. This can be counter-productive as it may stifle research into other areas (in this case gravity). When we take the "best current theory" and deride skeptics of it to the point that it discourages other areas of investigation, that's a bug, not a feature.
Our current understanding of gravity is woefully inadequate, as shown by our inability to reproducibly measure the gravitational constant as well as we should be able to with current technology. The flyby anomaly is another example where DM does not help. I hope that the current popularity of DM does not stifle research into gravity.
Where we run into trouble is by assigning too much credence (or too little skepticism) for that which has not been proven yet. This can be counter-productive as it may stifle research into other areas (in this case gravity). When we take the "best current theory" and deride skeptics of it to the point that it discourages other areas of investigation, that's a bug, not a feature.
Our current understanding of gravity is woefully inadequate, as shown by our inability to reproducibly measure the gravitational constant as well as we should be able to with current technology. The flyby anomaly is another example where DM does not help. I hope that the current popularity of DM does not stifle research into gravity.
Epicycles had low predictive power and was needlessly complicated compared to later theories, but it wasn't "nonsense"; the predictions the theory made about the relative positions of the Earth and planets were pretty accurate.
And thanks to our knowledge of Fourier Series we could come up with an even more accurate epicyclic model today! It's only when you try to explain tides or Lagrange points that a geocentric epicyclic model falls apart.
[deleted]
I feel like scientists today have forgotten a fundamental truth about science and understanding: We can never _know_ when we are right about our theories. We can only ever _know_ when we are wrong about them. New evidence can arrive at any time, and that evidence will either bolster our theories, or prove one or more theories incorrect. New evidence is always arriving.
I mean do we really believe that we know everything about this? Somehow, we A) know we have large knowledge gaps, AND B) believe that we understand things we have unanswered questions about.
We have a LOT of confidence about dark matter and exactly zero direct evidence.
It seems much more likely to me (I am not a scientist) that we are wrong about things that we assume to be hard facts and those error(s) have artificially produced the need for dark matter in order for things to make sense.
I mean do we really believe that we know everything about this? Somehow, we A) know we have large knowledge gaps, AND B) believe that we understand things we have unanswered questions about.
We have a LOT of confidence about dark matter and exactly zero direct evidence.
It seems much more likely to me (I am not a scientist) that we are wrong about things that we assume to be hard facts and those error(s) have artificially produced the need for dark matter in order for things to make sense.
> We can only ever _know_ when we are wrong about them.
I think this is what the OP is saying though: There are many ideas about what dark matter is or could be, but astrophysicists model the early universe using only baryonic matter, the results _are wrong_.
As a theory, it's quite simple: in its absence, the physics doesn't work. If you add matter that behaves in a particular way, simulations align to observation.
What is dark matter? shrug I don't think we can call any answer to that question a theory yet, we don't have any way to falsify it. We have many hypotheses, but those aren't theories.
I think this is what the OP is saying though: There are many ideas about what dark matter is or could be, but astrophysicists model the early universe using only baryonic matter, the results _are wrong_.
As a theory, it's quite simple: in its absence, the physics doesn't work. If you add matter that behaves in a particular way, simulations align to observation.
What is dark matter? shrug I don't think we can call any answer to that question a theory yet, we don't have any way to falsify it. We have many hypotheses, but those aren't theories.
> There are many ideas about what dark matter is or could be, but astrophysicists model the early universe using only baryonic matter, the results _are wrong_.
That doesn’t make any particular theory correct. It is only proof that our current model is wrong.
Filling the gaps with math, and calling the math “dark matter” does not make dark matter correct; one or more of our existing models is wrong.
That doesn’t make any particular theory correct. It is only proof that our current model is wrong.
Filling the gaps with math, and calling the math “dark matter” does not make dark matter correct; one or more of our existing models is wrong.
The name dark matter is not a specific thing, rather, it's a collection of hypotheses whose characteristics are bounded by results in high energy experiments and astronomical observation.
> As a theory, it's quite simple: in its absence, the physics doesn't work. If you add matter that behaves in a particular way, simulations align to observation.
They actually don't, numerous extra parameters have to be added for DM to account for observations. DM was invented to fix one problem with observation, and 15 more have cropped up which don't fit.
They actually don't, numerous extra parameters have to be added for DM to account for observations. DM was invented to fix one problem with observation, and 15 more have cropped up which don't fit.
What are those extra parameters?
See the paper [1] and the discussions of the times DM has been falsified. Extra parameters were then added to account for the new observations, where MOND makes certain parameter-free predictions that match observations. Clearly neither theory is a perfect fit for observations but the strong preference for DM seems unjustified.
[1] From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
[1] From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
Could you elaborate on where dark matter was "falsified"?
It’s not shtick, it makes perfect sense to me - unlike your post which has no substance.
Group-think does not equal truth.
Just because there is no compelling alternative theory does not make the Dark Matter Theory correct.
It’s probably nonsense, like many theories in Physics such as the Big Bang. Our level of intelligence and understanding, at the moment, is simply too small to comprehend the mysteries of the Universe that we live in.
Does this guy also reject DM models based on MACHOs?
I think they expect particles to be thrown out and result with slowdown but dark objects as massive as stars wouldn't be thrown at such a huge rate to observe slowdown, am I right?
I think they expect particles to be thrown out and result with slowdown but dark objects as massive as stars wouldn't be thrown at such a huge rate to observe slowdown, am I right?
There's only one way to find out. It involves reading the article.
I mean, what else could you bring to the discussion by only guessing what is being discussed?
I mean, what else could you bring to the discussion by only guessing what is being discussed?
I read it and I ask the question here because I didn't find the answer for it in the article.
The article just talks about particles and dismisses them.
I see nothing about DM composed of massive objects.
What exactly does your comment bring to the discussion?
The article just talks about particles and dismisses them.
I see nothing about DM composed of massive objects.
What exactly does your comment bring to the discussion?
So what would be a DM theory explanation of a lack of Chandrasekhar friction?
Do people actually believe in "Dark Matter" - or do they just believe in there being something that doesn't make sense and this is what explains it?
People actually believe that there is an yet-undiscovered substance that has mass but interacts very weakly (or not at all) with light, and that there are vast quantities of this substance in the universe. They call this "dark matter".
What's the difference?
The former will tend towards a defensive attachment to an idea which leads to, as Planck put it, "Science [advancing] one funeral at a time." The openness of the latter leads to less certainty, but greater ability for progress.
Consider the heliocentric/geocentric argument some centuries passed. Contrary to pop-science portrayals this wasn't an issue of Man against Church. The heliocentric view initially had numerous flaws and invalid assumptions. But because scientists of the time genuinely believed in the geocentric universe, they obsessed on these flaws and trying to use those to discredit the view, instead of impartially considering the idea and seeing if it could be patched and whether it would ultimately make more sense.
The "right" answer, with negligible refinement, can often look much worse than the wrong answer which has had decades, if not centuries of mass refinement. And that can drive those with a "belief" to the contrary, to want to attack it. The analogs outside of science are as endless as those within it.
Consider the heliocentric/geocentric argument some centuries passed. Contrary to pop-science portrayals this wasn't an issue of Man against Church. The heliocentric view initially had numerous flaws and invalid assumptions. But because scientists of the time genuinely believed in the geocentric universe, they obsessed on these flaws and trying to use those to discredit the view, instead of impartially considering the idea and seeing if it could be patched and whether it would ultimately make more sense.
The "right" answer, with negligible refinement, can often look much worse than the wrong answer which has had decades, if not centuries of mass refinement. And that can drive those with a "belief" to the contrary, to want to attack it. The analogs outside of science are as endless as those within it.
[deleted]
QI (quantized inertia) is a theory created by Mike McCulloch in the UK. It predicts galaxy rotations, including wide binaries extremely well, amongst other things. It is well worth a look.
This is a crackpot theory created by a known crackpot.
Why? Because you say so? With a dismissal like that you ought to elaborate with some evidence. Especially since you seem to be attacking the man, along with his theory.
He's associated with the EmDrive fraud, which should be sufficient for anyone to dismiss his ideas.
https://www.forbes.com/sites/briankoberlein/2017/02/15/quant...
https://arxiv.org/pdf/1908.01589.pdf
I'm not here to debate with physics cranks; further replies will not be read.
https://www.forbes.com/sites/briankoberlein/2017/02/15/quant...
https://arxiv.org/pdf/1908.01589.pdf
I'm not here to debate with physics cranks; further replies will not be read.
> * DM particle haven't yet been found.
We do not know that dark matter exists
> * The current best theory of the structure formation and galaxy evolution involves dark matter and critically depend on it to reproduce observations.
The stories we like to tell require dark matter. Otherwise our stories are wrong
> * There is a broad variety of Dark matter models that are consistent with simulations.
We have a lot of stories using dark matter. We really like it
> * It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.
Our stories are just stories but it is all we have
> * There are a few cases where you can find tensions with the existing DM based paradigm.
Our stories are not internally consistent.
> * A final point. Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.
We really like stories with dark matter
I love Astrophysics! Pure math with constraints. Do not confuse it with reality
We do not know that dark matter exists
> * The current best theory of the structure formation and galaxy evolution involves dark matter and critically depend on it to reproduce observations.
The stories we like to tell require dark matter. Otherwise our stories are wrong
> * There is a broad variety of Dark matter models that are consistent with simulations.
We have a lot of stories using dark matter. We really like it
> * It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.
Our stories are just stories but it is all we have
> * There are a few cases where you can find tensions with the existing DM based paradigm.
Our stories are not internally consistent.
> * A final point. Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.
We really like stories with dark matter
I love Astrophysics! Pure math with constraints. Do not confuse it with reality
All theories are stories. All communicated information is stories. Stories is just a word, it has pejorative meaning in context. Bible Stories are not like physics stories. A lot of physics stories are subject to test, null hypothesis, disproof.
The stories which persist are useful. Calling them theorems or theory helps us rei-fy stories into propositions which can be used to do science. Science is about modelling things, understanding things, and testing things. It is a valid proposition to argue DM is defined by stories which remain untestable, but the proposition there are better alternatives ignores that to construct stories without DM which are better will demand addressing the problems DM has to exist, to define the blank spaces in other, testable stories. You think Absolute zero exists? It's just a story. We haven't got there, we got close, we observe what happens, but this mythical zero point.. What good is it, if we can't get there? I love temperature, the whole thing depends on a fantasy...
Do not confuse your projection of "what is reality" with reality. I love HN, where people make asserts which don't mean what they think they mean!
The stories which persist are useful. Calling them theorems or theory helps us rei-fy stories into propositions which can be used to do science. Science is about modelling things, understanding things, and testing things. It is a valid proposition to argue DM is defined by stories which remain untestable, but the proposition there are better alternatives ignores that to construct stories without DM which are better will demand addressing the problems DM has to exist, to define the blank spaces in other, testable stories. You think Absolute zero exists? It's just a story. We haven't got there, we got close, we observe what happens, but this mythical zero point.. What good is it, if we can't get there? I love temperature, the whole thing depends on a fantasy...
Do not confuse your projection of "what is reality" with reality. I love HN, where people make asserts which don't mean what they think they mean!
> A lot of physics stories are subject to test, null hypothesis, disproof.
Nothing in astrophysics is like that, is there?
Nothing in astrophysics is like that, is there?
I'm not an astrophysicist. But I note, had Oppenheimer not died before it was confirmed at least one of his theories predicted black holes. He would have got a Nobel on it.
To me, thats a strong indication the fundamentals of mass, energy as modelled, were projected in advance of radio-telescopes confirming the theory. isn't that what Astrophysics does?
Perhaps there are better examples. Personally, I find the main sequence circular logic reasoning, but its a model for spectral colour, distance, age and size. I'd kind of like it if we flew a mission to hold a Pantone colour wheel up close, and measure the damn thing properly for size and colour but age is very hard. You're back in models of decay of mass/energy outcomes and how we believe half-life in C14 analysis.. except done as spectral lines at a distance based on one solar mass we have close by to model things on. Plus, we don't know how to make pantone colour stable across 20,000 years of flight time to measure a star up close and by then Humans will have 29 eyeballs seeing into the infrared like mantis shrimps.
Gravitational lensing is pretty cool. I think it was initially theoretical, and it was a long time being proved.
Gravity waves defy detectors. If we can get detectors working that will be immensely cool. I may have stepped off the scienting engine by wanting an outcome, which arguably is not aligned to null hypothesis testing. Maybe we can't detect gravity waves and they remain theory?
Look, its rude. I apologize in advance. I do kinda think you're trolling. Are you trolling? Maybe Dang will be upset at my asking. It's ok to ignore.
To me, thats a strong indication the fundamentals of mass, energy as modelled, were projected in advance of radio-telescopes confirming the theory. isn't that what Astrophysics does?
Perhaps there are better examples. Personally, I find the main sequence circular logic reasoning, but its a model for spectral colour, distance, age and size. I'd kind of like it if we flew a mission to hold a Pantone colour wheel up close, and measure the damn thing properly for size and colour but age is very hard. You're back in models of decay of mass/energy outcomes and how we believe half-life in C14 analysis.. except done as spectral lines at a distance based on one solar mass we have close by to model things on. Plus, we don't know how to make pantone colour stable across 20,000 years of flight time to measure a star up close and by then Humans will have 29 eyeballs seeing into the infrared like mantis shrimps.
Gravitational lensing is pretty cool. I think it was initially theoretical, and it was a long time being proved.
Gravity waves defy detectors. If we can get detectors working that will be immensely cool. I may have stepped off the scienting engine by wanting an outcome, which arguably is not aligned to null hypothesis testing. Maybe we can't detect gravity waves and they remain theory?
Look, its rude. I apologize in advance. I do kinda think you're trolling. Are you trolling? Maybe Dang will be upset at my asking. It's ok to ignore.
Wat... "Like" implies preference. You're using the word "story" to imply someone pulled it out of their imagination. What they said was "we currently have no plausible theories that doesn't require dark matter". These theories have to be consistent with other theories and observations.
plausibility is a bayesian prior
Different people have different priors. For some dark matter is more unlikely.
Different people have different priors. For some dark matter is more unlikely.
If they don't agree with the hole in the other theories which use DM to reconcile observations, thats an issue worth exploring. If they just don't like the DM label on those holes, its a fine point. What do you want to call the emerging shape in theory which is a hole, in otherwise very fine, testable propositions?
Indeed. That's why claiming that dark matter exists OR not exists is wrong. We do not know. The consensus is that it's more likely that it does.
I don't understand your point. You could say that about pretty much anything.
We really like to tell stories where 2+2=4, etc.
We really like to tell stories where 2+2=4, etc.
How do you not understand?
We know 2+2=4. We do not know that dark matter exists.
We know 2+2=4. We do not know that dark matter exists.
No, but we have a theory that predicts several things, including something like dark matter. It has been tested for several of it’s large scale predictions involving the movement of matter. Now we are testing it’s prediction of physical dark matter.
> We know 2+2=4
Which is why we really like telling stories about it.
My point is, we tell stories about literally everything, so i don't know what point you are trying to make.
If your criticism applies equally to basic facts, it is a bad criticism.
Which is why we really like telling stories about it.
My point is, we tell stories about literally everything, so i don't know what point you are trying to make.
If your criticism applies equally to basic facts, it is a bad criticism.
No one (here) is claiming that we know dark matter exists...
2+2=4 is only true under certain assumptions.
We also do not know that dark matter does not exist, which is the claim of the article.
We do know that dark matter, as constituted, in all its variations, requires observations grossly incompatible with what we, in fact, find.
Pop science cosmology presentations never, ever mention these contradictions. But it is, exactly, embracing contradictions like these that would make it science, not religion. Presentations without them actively mislead the public as to what science is and is for.
Trotting out details found (or made) consistent with DM amounts to indulging confirmation bias. An honest presentation describes the current favored theory, which summarizes a collection of observations, and then whatever is inconsistent with it. Sweeping inconsistent facts under the rug is the opposite of science.
Every substantial advance has come from embracing contradictions of current favored theories. Young people are inspired not by sweeping, broad-brush stories of how the universe is, but by mysteries that remind us how much is left to be discovered.
Biologists understand this. It is very easy to get a biologist to say "nobody knows". Every non-moribund field revels in what is still wholly unknown. Only cosmology circles the wagons against contradictory evidence.
Pop science cosmology presentations never, ever mention these contradictions. But it is, exactly, embracing contradictions like these that would make it science, not religion. Presentations without them actively mislead the public as to what science is and is for.
Trotting out details found (or made) consistent with DM amounts to indulging confirmation bias. An honest presentation describes the current favored theory, which summarizes a collection of observations, and then whatever is inconsistent with it. Sweeping inconsistent facts under the rug is the opposite of science.
Every substantial advance has come from embracing contradictions of current favored theories. Young people are inspired not by sweeping, broad-brush stories of how the universe is, but by mysteries that remind us how much is left to be discovered.
Biologists understand this. It is very easy to get a biologist to say "nobody knows". Every non-moribund field revels in what is still wholly unknown. Only cosmology circles the wagons against contradictory evidence.
I don't think i have ever heard anyone claim we know for sure. I have heard lots of physicists claim that its the best theory they are aware of given evidence they have seen, which is a really different claim.
> Biologists understand this. It is very easy to get a biologist to say "nobody knows"
Depends on what you ask them about.
> Biologists understand this. It is very easy to get a biologist to say "nobody knows"
Depends on what you ask them about.
Most things you can ask them, they have no answer for. They revel in it.
Anything which gives good prediction power is useful.
Given we can't observe reality directly, since we ourselves see it though a model, We can adapt the above list to everything.
The question isn't "is it a story" the question is "is it useful for prediction"
Much of astrophysics has been.
Given we can't observe reality directly, since we ourselves see it though a model, We can adapt the above list to everything.
The question isn't "is it a story" the question is "is it useful for prediction"
Much of astrophysics has been.
We do not know that reality exists.
[deleted]
Start with an ad hominem, continue with this:
> Without such theory, claiming DM doesn't exist is simply stupid IMO.
Expressing flaws in an idea does not require a better one in any way. The search continues.
> Without such theory, claiming DM doesn't exist is simply stupid IMO.
Expressing flaws in an idea does not require a better one in any way. The search continues.
Expressing flaws doesn't require a better theory, no. By all means, do that.
Expecting others to give up their theories that work well for 99% of the problem, or even only work well for the 10% they care about, just because there's a problem with it DOES require something better AND a reason to switch.
For example, architects (technically stability engineers. Architects don't really design buildings except in the artistic sense) are still simulating Newtonian dynamics on plates that fly through empty space held up by nothing. You want them to change? No problem, but you'll have to make something better and point out why they'd want to use something better ... but, truthfully, it works pretty well.
Expecting others to give up their theories that work well for 99% of the problem, or even only work well for the 10% they care about, just because there's a problem with it DOES require something better AND a reason to switch.
For example, architects (technically stability engineers. Architects don't really design buildings except in the artistic sense) are still simulating Newtonian dynamics on plates that fly through empty space held up by nothing. You want them to change? No problem, but you'll have to make something better and point out why they'd want to use something better ... but, truthfully, it works pretty well.
The piece says, thing X doesn't exist, here's how it was already figured out, etc. We should find something better. I don't think it says we aren't allowed to keep it around when it is sometimes useful as a thought device.
It also reduces the religious aspect, demoting DM to simply a tool used in specific situations, "we don't have anything better at the moment."
It also reduces the religious aspect, demoting DM to simply a tool used in specific situations, "we don't have anything better at the moment."
What if the "dark matter" is actually ions not observable from our telescopes? Plasma Physics hold ions permeating the Universe as a premise & has physical experiments reproducable in the lab to back up their claims...And can use classical EM equations explain how the stars & galaxies work instead of some novel Physics which needs constructs such as "Dark Matter" to balance the equations...
> What if the "dark matter" is actually ions not observable from our telescopes?
We have radio telescopes that can see all the way down to a few tens of MHz. This is far colder than the CMB, and certainly much too cold for the intergalactic medium.
> Plasma Physics hold ions permeating the Universe as a premise & has physical experiments reproducable in the lab to back up their claims
Yes, plasmas exist. There are lots of them in space. This is completely uncontroversial.
> And can use classical EM equations explain how the stars & galaxies work
Absolutely not. Galaxies are firmly in the nonclassical regime.
We have radio telescopes that can see all the way down to a few tens of MHz. This is far colder than the CMB, and certainly much too cold for the intergalactic medium.
> Plasma Physics hold ions permeating the Universe as a premise & has physical experiments reproducable in the lab to back up their claims
Yes, plasmas exist. There are lots of them in space. This is completely uncontroversial.
> And can use classical EM equations explain how the stars & galaxies work
Absolutely not. Galaxies are firmly in the nonclassical regime.
> We have radio telescopes that can see all the way down to a few tens of MHz. This is far colder than the CMB, and certainly much too cold for the intergalactic medium.
PV = nRT
What if the P is very low & V is very big...like it is in space? What would the plasma in dark discharge radiate?
> Absolutely not. Galaxies are firmly in the nonclassical regime.
According to some models. Do these models have reproducible experimental evidence? If not, I don't see how you can credibly be so sure of yourself...
Sure, exotic & speculative math is way more fun than reconciling with physical reality. Without reproducible experimental evidence, the model is non-falsifiable (& non-provable).
In contrast, the Plasma model does have physically reproducible experiments that are able to create galactic phenomena in the lab. Live physical experimentation...not computer simulations using math that has never been verified by physical experiment.
PV = nRT
What if the P is very low & V is very big...like it is in space? What would the plasma in dark discharge radiate?
> Absolutely not. Galaxies are firmly in the nonclassical regime.
According to some models. Do these models have reproducible experimental evidence? If not, I don't see how you can credibly be so sure of yourself...
Sure, exotic & speculative math is way more fun than reconciling with physical reality. Without reproducible experimental evidence, the model is non-falsifiable (& non-provable).
In contrast, the Plasma model does have physically reproducible experiments that are able to create galactic phenomena in the lab. Live physical experimentation...not computer simulations using math that has never been verified by physical experiment.
> PV = nRT
For an ideal gas. Plasmas are extremely far from being ideal gases.
> According to some models. Do these models have reproducible experimental evidence?
Yes, general relativity is extremely well supported by the evidence.
For an ideal gas. Plasmas are extremely far from being ideal gases.
> According to some models. Do these models have reproducible experimental evidence?
Yes, general relativity is extremely well supported by the evidence.
Last I understood (I am not an expert) MOND and related theories fails to explain certain observed phenomena, and goes against other experimentally verified laws/phenomena.
PBS Spacetime covers this topic in several videos, a good one being [1]. Matt (the host, an astrophysicist), describes what MOND (and other alternative theories, like relativistic-MOND) needs to do but haven't done yet:
1. Give the right answer in more than one special case. MOND may describe a few situations accurately, but it does not describe all situations where we have evidence for dark matter. Only some.
2. Consistent with other known laws and theories that are experimentally verified. According to Matt and others, MOND is not consistent with existing laws such as conservation of energy or angular momentum.
3. Make testable predictions beyond what it was tuned for.
Am I missing out on some extraordinary development in MOND and/or MOND-like theories that occurred recently?
[1] https://www.youtube.com/watch?v=0sTBZ2G4vow
PBS Spacetime covers this topic in several videos, a good one being [1]. Matt (the host, an astrophysicist), describes what MOND (and other alternative theories, like relativistic-MOND) needs to do but haven't done yet:
1. Give the right answer in more than one special case. MOND may describe a few situations accurately, but it does not describe all situations where we have evidence for dark matter. Only some.
2. Consistent with other known laws and theories that are experimentally verified. According to Matt and others, MOND is not consistent with existing laws such as conservation of energy or angular momentum.
3. Make testable predictions beyond what it was tuned for.
Am I missing out on some extraordinary development in MOND and/or MOND-like theories that occurred recently?
[1] https://www.youtube.com/watch?v=0sTBZ2G4vow
The article is not about MOND, it is about the falsification of Dark Matter. They do advocate MOND, but the main takeaway is right up front:
> The current cosmological model only works by postulating the existence of dark matter – a substance that has never been detected, but that is supposed to constitute approximately 25% of all the universe. But a simple test suggests that dark matter does not in fact exist. If it did, we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particles, but we detect no such slow-down. A host of other observational tests support the conclusion: dark matter is not there.
> The current cosmological model only works by postulating the existence of dark matter – a substance that has never been detected, but that is supposed to constitute approximately 25% of all the universe. But a simple test suggests that dark matter does not in fact exist. If it did, we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particles, but we detect no such slow-down. A host of other observational tests support the conclusion: dark matter is not there.
The article tries to conclusively throw out good and predictive science based on a single rare edge case test that well-educated people believe to be explainable within the same paradigm.
If you're going to claim that dark matter doesn't exist, you need to have a way to explain all of the cases that are known to show that dark matter does exist. Cases like the Bullet Cluster, where a collision left all of the visisble matter in one region, and all of the gravitational matter in another. How can this possibly happen if there is no such thing as invisible gravitational matter? How can there be galaxies like AGC 114905 that don't have any dark matter, if there is no such thing as dark matter for galaxies to have or not?
If you're going to claim that dark matter doesn't exist, you need to have a way to explain all of the cases that are known to show that dark matter does exist. Cases like the Bullet Cluster, where a collision left all of the visisble matter in one region, and all of the gravitational matter in another. How can this possibly happen if there is no such thing as invisible gravitational matter? How can there be galaxies like AGC 114905 that don't have any dark matter, if there is no such thing as dark matter for galaxies to have or not?
No, you don't need to explain anything.
DM falsehood does not depend on any other known thing being correct. It particularly does not depend on MOND being correct.
The honest fallback position is not "this other thing is better", it is, "We do not know. We had hoped we did, but were wrong." Then, start entertaining hypotheses that encompass all observations, without prejudice, not just favored ones.
DM falsehood does not depend on any other known thing being correct. It particularly does not depend on MOND being correct.
The honest fallback position is not "this other thing is better", it is, "We do not know. We had hoped we did, but were wrong." Then, start entertaining hypotheses that encompass all observations, without prejudice, not just favored ones.
[deleted]
So if DM is falsified and MOND is unworkable, what should scientists do? Just admit that they have no idea what's going on, but it looks a lot like missing mass?
Oh wait, that's the definition of dark matter.
Oh wait, that's the definition of dark matter.
>Just admit that they have no idea what's going on, but it looks a lot like missing mass?
The way I see things, the much more prevalent attitude is, "we have a good idea of what's going on, we just haven't been able to confirm our confident assessments with objective data". Very few, if any, prominent people in the field admit, "we don't have any idea what's going on, it is all baseless conjecture that might pan out if 75% of the universe is made of some invisible stuff that we haven't been able to detect in 4 decades despite our best efforts". I'd like to see a paradigm shift from, "we have a good understanding of how things work, now we just need to detect the invisible particles that make all of our formulas work" to "we have really have no idea what is happening, but here is some wild speculation that is the best we can come up with".
A lot of the "dark matter" debate reminds me of the Alzheimers/amyloid situation. Groupthink develops among the establishment in the field, based on very little (if any) objective proof, which ends up discouraging and marginalizing those who pursue other theories.
The way I see things, the much more prevalent attitude is, "we have a good idea of what's going on, we just haven't been able to confirm our confident assessments with objective data". Very few, if any, prominent people in the field admit, "we don't have any idea what's going on, it is all baseless conjecture that might pan out if 75% of the universe is made of some invisible stuff that we haven't been able to detect in 4 decades despite our best efforts". I'd like to see a paradigm shift from, "we have a good understanding of how things work, now we just need to detect the invisible particles that make all of our formulas work" to "we have really have no idea what is happening, but here is some wild speculation that is the best we can come up with".
A lot of the "dark matter" debate reminds me of the Alzheimers/amyloid situation. Groupthink develops among the establishment in the field, based on very little (if any) objective proof, which ends up discouraging and marginalizing those who pursue other theories.
> Oh wait, that's the definition of dark matter.
No, actually calling it missing mass is dark matter. MOND would be another explanation, and there's no reason to conclude it's unworkable.
No, actually calling it missing mass is dark matter. MOND would be another explanation, and there's no reason to conclude it's unworkable.
MOND still need dark matter, it seems
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
That's not what you can infer from the data. Some observations fit well with MOND, some with dark matter. See:
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
They are advocating MOND by omission. If you say dark matter isn't there you now need a theory that can explain all the observations that do support dark matter. MOND seems to be the only semi reasonable alternative.
It's perfectly reasonable to say, "your theory is full of holes and isn't based on anything objective that can be measured or proved" without coming up with an alternative theory. You can (and should in my opinion) point out things that are baseless conjecture whether or not you have a better idea. "I don't know" is something a lot of us would be better off saying more often.
I agree, it's fine to point out holes in a theory without an alternative explanation. However, it does still leave the problem of how else do you explain all the dark matter observations. So one must be careful not to give to much weight to those kinds of criticisms, as finding one hole in something that explains ten observations doesn't give much confidence in saying the whole theory is wrong (just an example.) Dark matter still seems a much better explanation than MOND to date, even if I personally feel it looks like a hack.
>They do advocate MOND
Which is why I'm asking about MOND, which I just explained in my comment is falsified from the start (violation of existing established physics).
Which is why I'm asking about MOND, which I just explained in my comment is falsified from the start (violation of existing established physics).
I don't think MOND proponents say the theory is complete, just that alternative gravitation theories is the direction that should be taken for research instead of funding futile dark matter detection projects.
>alternative gravitation theories is the direction that should be taken for research instead of
Why instead of? Dark matter is, so far, the best model we have. Seems sensible to continue research in that direction.
>futile dark matter detection projects.
Why are they futile?
Why instead of? Dark matter is, so far, the best model we have. Seems sensible to continue research in that direction.
>futile dark matter detection projects.
Why are they futile?
In the context of this article, evaluating the no-dark-matter future is probably in scope.
In general, that statement would require defense.
In general, that statement would require defense.
The article writes upfront: "The implications of this are nothing short of a revision of Einstein’s theory of gravitation."
> 1. Give the right answer in more than one special case. MOND may describe a few situations accurately, but it does not describe all situations where we have evidence for dark matter. Only some.
DM also fails numerous observations, like the one described in this article, external field effects, and more. It failed numerous previous observations as well until more parameters were added to DM theories to account for actual observations.
> 3. Make testable predictions beyond what it was tuned for.
This is backwards. DM has been tuned to match certain predictions, where MOND's predictions are free of parameters and yet fit observations. That's actually strong evidence in favour of MOND.
See my other comments here for a reference to a paper that reviews the evidence for/against both.
DM also fails numerous observations, like the one described in this article, external field effects, and more. It failed numerous previous observations as well until more parameters were added to DM theories to account for actual observations.
> 3. Make testable predictions beyond what it was tuned for.
This is backwards. DM has been tuned to match certain predictions, where MOND's predictions are free of parameters and yet fit observations. That's actually strong evidence in favour of MOND.
See my other comments here for a reference to a paper that reviews the evidence for/against both.
Take it up with the astrophysicists who gave this criteria, not me. Unless you are also an astrophysicist, I'll stick with trusting their judgement over yours. You can also watch the video I provided for a more nuanced explanation.
Here's your nuanced review by astrophysicists:
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
If someone were to ask me I'd say I embraced the scientific consensus that dark matter is real, but in my heart of hearts I have to admit that it smells like phlogiston and aether to me, and its lack of falsifiability is not something I can ignore.
> I have to admit that it smells like phlogiston and aether to me
You know what else smells like phlogiston? Oxygen. There really is an invisible, odorless, tasteless gas responsible for combustion, plant growth, and breathing. 17th century chemists thought that it was released during combustion, absorbed by plants, and expelled by the lungs. Turns out it's absorbed during combustion, released by plants, and taken in by the lungs.
Phlogiston was a reasonable theory, well supported by the available evidence at the time. It was also wrong. Most theories are. But this could not have possibly been predicted a priori.
You know what else smells like phlogiston? Oxygen. There really is an invisible, odorless, tasteless gas responsible for combustion, plant growth, and breathing. 17th century chemists thought that it was released during combustion, absorbed by plants, and expelled by the lungs. Turns out it's absorbed during combustion, released by plants, and taken in by the lungs.
Phlogiston was a reasonable theory, well supported by the available evidence at the time. It was also wrong. Most theories are. But this could not have possibly been predicted a priori.
It seems so incredibly unsurprising and mundane that given the particle zoo that we have that it might include a set of particles that interact very weakly with the electromagnetic field and so are extremely difficult for us to directly detect.
That of course doesn't say one way or another that such hypothetical particles can account for the amount of mass needed.
That of course doesn't say one way or another that such hypothetical particles can account for the amount of mass needed.
If all that was needed was extra mystery mass sprinkled everywhere, there would be little problem.
The exact problem is that sprinkling extra mystery mass everywhere produces results inconsistent with observation.
The exact problem is that sprinkling extra mystery mass everywhere produces results inconsistent with observation.
About the falsibility - we have a paper with a method to disprove dark matter right here. There are many different cosmological observations which demonstrate deviations between expected and measured gravity, and they are only getting more numerous. If one theory can explain them all, that would already be a big accomplishment. Dark matter seems to explain more than any competitor, but as I understand it no theory seems to fit perfectly.
We have the claim of a refutation here, but one that is obviously weak. If your only explanation of why your toy theory is rejected by everyone else is collective, universal delusion you've already disproven yourself.
No theory fits perfectly, but that is what we expect in a world of imperfect knowledge.
No theory fits perfectly, but that is what we expect in a world of imperfect knowledge.
The science of their method to disprove dark matter is really pretty good. The problem is how they present other scientists as foolish for holding onto dark matter theory. More researchers should definitely take a look at the evidence. There are some strong reasons why dark matter is the favored model, and it needs to be a strong refutation to rule it out. If other contenders like MOND didn't also have significant problems of their own, people would also be more eager to lend them credibility instead of dark matter.
This is the same situation as when special relativity was being developed. The equations for the mechanical theory of the aether looked exactly the same as the equations for special relativity. Similarly any modified gravity theory will be identical to a dark matter theory, except for the motivating principles.
So far modified gravity theories can’t explain everything. That and they would have to integrate with general relativity for which evidence is only getting stronger.
So far modified gravity theories can’t explain everything. That and they would have to integrate with general relativity for which evidence is only getting stronger.
The whole idea of a "scientific consensus" is flawed as it's being used. Here, DM is the dominant theory in the scientific community at this time, but there are strong arguments against it, how can one call that a "consensus"? It's just the dominant theory.
Can someone with the appropriate background please confirm or refute?
"But a simple test suggests that dark matter does not in fact exist. If it did, we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particles, but we detect no such slow-down."
Is that hypothesis correct? (i.e. would we expect lighter galaxies orbiting heavier ones to slow down if dark matter exists)
If it is correct, and we don't observe that effect, would it not be a very strong argument refuting the existence of dark matter?
For folks mentioning this as a "crackpot" or "anti-dm" theory, is the strong claim that the hypothesis is incorrect?
Is that hypothesis correct? (i.e. would we expect lighter galaxies orbiting heavier ones to slow down if dark matter exists)
If it is correct, and we don't observe that effect, would it not be a very strong argument refuting the existence of dark matter?
For folks mentioning this as a "crackpot" or "anti-dm" theory, is the strong claim that the hypothesis is incorrect?
I've read nearly every comment here and no one seems to have an answer... It is a very convincing argument, to be honest.
There are phenomena in the universe that, for example, general relativity does not predict correctly. Is your conclusion that we should discard any useful theory which ever fails to match an observation?
Would someone who relied on Newtonian dynamics 100 years ago likewise be incorrect to do so because it failed to explain many aspects of planetary motion?
Would someone who relied on Newtonian dynamics 100 years ago likewise be incorrect to do so because it failed to explain many aspects of planetary motion?
No one is suggesting anything should be discarded. Just that the null hypothesis be tested.
Yup, no one still seems to have an answer to a simple, straightforward question, and the lack of any convincing counterargument makes it even more convincing.
I hesitate to respond to you because your tone seems especially combative.
It is well known that the relevant wake friction calculation ("classical Chandrasekhar") is for a pointlike structureless body. Satellite galaxies and their parents are not this. Importantly satellites can lose matter and thus mass, so one has to correct for the evaporation and tidal loss (especially to the halo) of the satellite galaxy; and the host galaxy's potential grows adiabatically over the lifetime of the system.
If the density of the halo and other sparse matter increases closer to the host galaxy, inward migration of the satellite sees two effects driven by the collision into more particles: more satellite mass is torn off by tidal interactions and more halo particles surrounding the host are swept into the satellite's wake. All that matter stays well above the surface of the host galaxy rather than descending into some inner halo or deep into the host galaxy itself. This serves to "suspend" the sinking satellite, posing a challenge for the "they should sink" reasoning; it also reduces the amplitude of the wake, which moderates the drag on the satellite. The combined result is that the evolution of specific angular momentum may not be enough to clearly support Kroupa's claim in the fine article linked at the top.
There has been a lively dialogue in academic publications about the scale of these effects for some twenty-five years. Kroupa's article touches upon his own position in these, but not those of others (e.g. HS Zhao, Binney) who work and publish in the area (with all of the above citing one another from time to time).
I don't mind this at all, personally, as at worst Kroupa is omitting something an interested reader could hunt down her- or himself, and after all it was "only" published on a general interest site whose present front page (https://iai.tv/articles) has an article by Eric "electric universe" Lerner entitled "The Big Bang Didn't Happen".
It is well known that the relevant wake friction calculation ("classical Chandrasekhar") is for a pointlike structureless body. Satellite galaxies and their parents are not this. Importantly satellites can lose matter and thus mass, so one has to correct for the evaporation and tidal loss (especially to the halo) of the satellite galaxy; and the host galaxy's potential grows adiabatically over the lifetime of the system.
If the density of the halo and other sparse matter increases closer to the host galaxy, inward migration of the satellite sees two effects driven by the collision into more particles: more satellite mass is torn off by tidal interactions and more halo particles surrounding the host are swept into the satellite's wake. All that matter stays well above the surface of the host galaxy rather than descending into some inner halo or deep into the host galaxy itself. This serves to "suspend" the sinking satellite, posing a challenge for the "they should sink" reasoning; it also reduces the amplitude of the wake, which moderates the drag on the satellite. The combined result is that the evolution of specific angular momentum may not be enough to clearly support Kroupa's claim in the fine article linked at the top.
There has been a lively dialogue in academic publications about the scale of these effects for some twenty-five years. Kroupa's article touches upon his own position in these, but not those of others (e.g. HS Zhao, Binney) who work and publish in the area (with all of the above citing one another from time to time).
I don't mind this at all, personally, as at worst Kroupa is omitting something an interested reader could hunt down her- or himself, and after all it was "only" published on a general interest site whose present front page (https://iai.tv/articles) has an article by Eric "electric universe" Lerner entitled "The Big Bang Didn't Happen".
Thank you for the informative and thoughtful response. My comment and question was certainly not intended to be combative. I was genuinely curious for a perspective quite like the one you provided above, because it seemed odd that a claim so strong would not have a counter view given the active area of research. I think the original article would benefit from some perspective like the one you provided. While you're aware of the relevant threads of research that balance out the view in the original article, for someone not familiar with that even things that one would consider "well known" will not be so.
The view you provided helps understand the counter argument of why competing factors (e.g. losing mass) result in more sophisticated outcomes than "we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particle". I still don't know enough about the subject to understand if the original authors claim and expectation is still likely. But your context helps me understand other factors that are in play.
The view you provided helps understand the counter argument of why competing factors (e.g. losing mass) result in more sophisticated outcomes than "we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particle". I still don't know enough about the subject to understand if the original authors claim and expectation is still likely. But your context helps me understand other factors that are in play.
> and no one seems to have an answer
Especially DM proponents!
Especially DM proponents!
As a complete physics layperson, I can’t comment with any authority on the subject matter.
What I do have is a metric fuckton of experience with incentives and mechanism design in technical fields: and mainstream physicists have been talking like people who have bonuses linked to specific outcomes for decades.
The moving goalposts around falsifiability, the too-coincidental synergies between supersymmetric-style (and there for string world) stuff and missing mass (dark matter), the growing group of highly-qualified skeptics, the curt public dismissals everything from LQG to constructor stuff to MOND as beneath refutation, the popularizers who go on PBS and don’t even acknowledge a debate.
And the alternative explanation, that it takes so long to learn this stuff that your career is over if Dark Matter or String Theory turns out to be hokum? Yeah, that scans.
What I do have is a metric fuckton of experience with incentives and mechanism design in technical fields: and mainstream physicists have been talking like people who have bonuses linked to specific outcomes for decades.
The moving goalposts around falsifiability, the too-coincidental synergies between supersymmetric-style (and there for string world) stuff and missing mass (dark matter), the growing group of highly-qualified skeptics, the curt public dismissals everything from LQG to constructor stuff to MOND as beneath refutation, the popularizers who go on PBS and don’t even acknowledge a debate.
And the alternative explanation, that it takes so long to learn this stuff that your career is over if Dark Matter or String Theory turns out to be hokum? Yeah, that scans.
Not so different from Alzheimer's researchers continuing to give one another federal grants for ways to block production of amyloids decades after it has been shown to be a dead end. One wonders what all those amyloid biochemists can do with themselves once amyloid grants finally go away.
I'm an astrophysicist. I love the idea of shaking up how we do science, but MOND models really aren't that compelling for a practicing scientist (I would love to be wrong). I periodically consider working a modified gravity project, but it never seems that interesting. Maybe I can lay out my personal impressions for you in a software analogy.
There are simple situations where physics can be reasonably distinguished from the noise. Think Newton watching an apple fall from a tree -- these are test harnesses with a debugger and careful control of the environment. There are also astrophysical situations where it's very hard to squeeze insight out of the chaos. Instead of looking at an apple to derive Newtonian gravity, imagine instead trying to figure gravity out by looking at a flock of birds. There are tricky things in the way of our understanding, like lift, turbulence, and biomechanics. We hope to understand the bad situations someday, but right now it's tough. Instead of the nice test harness, these situations are like debugging through cryptic, un-reproducible user complaints. What's their OS? Do they have the right drivers installed? Do they have all of their ports blocked for some reason?
In astrophysics, one nice system is the Universe at very large scales: echos of the big bang, the clustering of matter, and the formation of structure. We have great data these days about the large scales, and general relativity (GR) + dark matter (DM) is a very predictive model here. To our chagrin, the data always matches the theory. It takes 5 or 6 parameters, but the model has withstood huge improvements in data quality without really changing since the 90s. The other nice situation is the small scales like our own solar system: we can measure things extremely precisely at home, and again GR works remarkably well. There are a few other good situations involving objects like pulsars. Finally there are the hard situations: intermediate scales that involve the messy physics of star and galaxy formation. We don't really know how these processes work, but we can cobble together simple models with DM that sort of match the data.
Modified gravities in the literature always seem to act exactly like general relativity + dark matter in the clean, understandable situations, although it takes various contortions (screening) for these models to do this. Modified gravity models seem to only act differently in the bad arenas that are hard to understand, when there trickier issues like galaxy and star formation. That's deeply suspicious, and really weakens the value proposition of these alternatives. It's like introducing a software feature to fix something that never happens on the dev machine, based on mysterious user reports that you can only half decipher.
There are simple situations where physics can be reasonably distinguished from the noise. Think Newton watching an apple fall from a tree -- these are test harnesses with a debugger and careful control of the environment. There are also astrophysical situations where it's very hard to squeeze insight out of the chaos. Instead of looking at an apple to derive Newtonian gravity, imagine instead trying to figure gravity out by looking at a flock of birds. There are tricky things in the way of our understanding, like lift, turbulence, and biomechanics. We hope to understand the bad situations someday, but right now it's tough. Instead of the nice test harness, these situations are like debugging through cryptic, un-reproducible user complaints. What's their OS? Do they have the right drivers installed? Do they have all of their ports blocked for some reason?
In astrophysics, one nice system is the Universe at very large scales: echos of the big bang, the clustering of matter, and the formation of structure. We have great data these days about the large scales, and general relativity (GR) + dark matter (DM) is a very predictive model here. To our chagrin, the data always matches the theory. It takes 5 or 6 parameters, but the model has withstood huge improvements in data quality without really changing since the 90s. The other nice situation is the small scales like our own solar system: we can measure things extremely precisely at home, and again GR works remarkably well. There are a few other good situations involving objects like pulsars. Finally there are the hard situations: intermediate scales that involve the messy physics of star and galaxy formation. We don't really know how these processes work, but we can cobble together simple models with DM that sort of match the data.
Modified gravities in the literature always seem to act exactly like general relativity + dark matter in the clean, understandable situations, although it takes various contortions (screening) for these models to do this. Modified gravity models seem to only act differently in the bad arenas that are hard to understand, when there trickier issues like galaxy and star formation. That's deeply suspicious, and really weakens the value proposition of these alternatives. It's like introducing a software feature to fix something that never happens on the dev machine, based on mysterious user reports that you can only half decipher.
In fairness the fine-tuning / epistemology / scientific method tap dancing seems to affect the string/supersymmetry crowd a lot more than the astrophysics crowd. The crossover act seems to be superpartners as WIMP candidates. My original comment didn’t reflect that.
Five or six freely chosen parameters is a lot. You know the von Neumann quote. If those parameters have continued to fit vastly more precise measurements without changing for 30 years that’s starting to sound like failure to falsify.
And if so, ultimately you folks have posed the particle/high-energy folks a problem: we found a shitload of weakly/non-interacting mass, where’s my particle bruh?
To the layperson, exotic undetectable mass sounds like something that will turn out to be a good metaphor for something deeper, but that doesn’t mean a lot via the definition of layperson.
Even laypeople know the string folks are full of shit: Witten has a Fields and not a Nobel for a reason.
Five or six freely chosen parameters is a lot. You know the von Neumann quote. If those parameters have continued to fit vastly more precise measurements without changing for 30 years that’s starting to sound like failure to falsify.
And if so, ultimately you folks have posed the particle/high-energy folks a problem: we found a shitload of weakly/non-interacting mass, where’s my particle bruh?
To the layperson, exotic undetectable mass sounds like something that will turn out to be a good metaphor for something deeper, but that doesn’t mean a lot via the definition of layperson.
Even laypeople know the string folks are full of shit: Witten has a Fields and not a Nobel for a reason.
To me, this is the cost of discovery. Just like a game of chess, you have to spend a lot of energy/cost thinking about lines that will not come to fruition to find the correct path.
Poor Alzheimer's research was/is stunted for a few people at the top pushing the wrong path. We'll see if that's the case for DM vs MOND vs something else.
Money will always be distributed to the wrong areas, but as long as you believe the human race to exist far into the future, it will eventually work itself out.
Poor Alzheimer's research was/is stunted for a few people at the top pushing the wrong path. We'll see if that's the case for DM vs MOND vs something else.
Money will always be distributed to the wrong areas, but as long as you believe the human race to exist far into the future, it will eventually work itself out.
This is very cynical but there's some truth to it. I also believe that it's less conscious. Once people accept an idea they're conditioned to think of it as true, and then when jobs and institutions revolved around that it amplifies aberrations. Maybe String Theory is total bupkiss, a lot of people are going to have a hard time with it.
But with this subject we're at least working with observable data ...
But with this subject we're at least working with observable data ...
Network effects can yield delusion and fraud without the participants consciously trying for it.
Dark Matter gravitational lensing seems pretty convincing.
https://www.nasa.gov/content/discoveries-highlights-shining-...
We have gravitational lensing, but that cannot save DM from other observations fundamentally incompatible with its premise.
Clinging to a single dominant theory is religious orthodoxy, not science. The essence of science is, "we don't pretend to know what we don't". There is plenty we do, that doesn't depend on DM.
Clinging to a single dominant theory is religious orthodoxy, not science. The essence of science is, "we don't pretend to know what we don't". There is plenty we do, that doesn't depend on DM.
Also, the research done regarding weakly interacting massive particles has been very interesting to follow the past couple of years
https://you.com/search?q=Weakly+Interacting+Massive+Particle...
https://you.com/search?q=Weakly+Interacting+Massive+Particle...
I know nothing of astrophysics and my opinion counts for shithole.
But DM has always reminded me of aether (https://en.m.wikipedia.org/wiki/Aether_(classical_element)) - a magical element that we add to current understanding of physics to correct for errors caused by missing knowledge. DM sounds so magical that it feels like an unknown force akeen to gravitation.
But once again, I don't know anything about this, so, who cares.
But DM has always reminded me of aether (https://en.m.wikipedia.org/wiki/Aether_(classical_element)) - a magical element that we add to current understanding of physics to correct for errors caused by missing knowledge. DM sounds so magical that it feels like an unknown force akeen to gravitation.
But once again, I don't know anything about this, so, who cares.
I will start by saying that I know very little about theoretical physics so I could be totally off here. But to me the idea of dark matter feels a little like the theory of ether[1]. Basically we observed a behavior we couldn’t explain, so we create a new invisible substance that permeates the cosmos to fill the hole in our scientific world view. It turned out that we just didn’t understand the science well enough, and there was no ether out there in the first place. Dark matter feels like too convenient of an explanation given that we have never detected it.
[1] https://en.m.wikipedia.org/wiki/Aether_theories
[1] https://en.m.wikipedia.org/wiki/Aether_theories
It's exactly like the theory of the ether. It was the fleshing-out of that theory that made physicists doubt its veracity - a substance must permeate all space, be more rigid than steel yet not impede planets orbiting the sun? Really? The Michelson-Morley experiment put the final nail in ether's coffin - but there were already a number of nails. On the upside, it led to great physics! Let's hope we'll be able to say the same for Dark Matter.
A similar contradiction does not yet exist for Dark Matter, so it is not exactly like ether
You have this entirely backward.
Ether was introduced because, previously, all other wave motion was waving something. It was standard issue. Waves in the ocean? Must be waving something. Waves in air? Must be waving something. Positing that there was nothing there "waving" would be the new thing.
Second, introduction of a "thing," only to find out that it is real is quite common. Witness the neutrino -- originally just a placeholder to make the math work.
Ether was introduced because, previously, all other wave motion was waving something. It was standard issue. Waves in the ocean? Must be waving something. Waves in air? Must be waving something. Positing that there was nothing there "waving" would be the new thing.
Second, introduction of a "thing," only to find out that it is real is quite common. Witness the neutrino -- originally just a placeholder to make the math work.
How is that any different? Sounds like "dark matter was introduced because, previously, all other matter interaction was pulling on something". It walks invisibly but quacks like matter (lensing, galaxy geometry, etc) so we call it dark matter.
It's all the ways in which it doesn't act like matter which make it interesting.
It's all the ways in which it doesn't act like matter which make it interesting.
Or similar to the way that we discovered Neptune and Pluto existed?
I wanted to read more about this 'Mond' thing and found this article <https://phys.org/news/2022-07-dark-ditch-favor-theory-gravit...>, which seems to be well written and at my level.
And this wikipedia article, <https://phys.org/news/2022-07-dark-ditch-favor-theory-gravit...>, seems to give a more balanced appraisal.
And this wikipedia article, <https://phys.org/news/2022-07-dark-ditch-favor-theory-gravit...>, seems to give a more balanced appraisal.
You included the same link twice. I'm guessing you wanted this one: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
To people saying the Dark Matter sounds like aether, phlogiston, or miasma, I have to wonder. Dark Matter is simply something that isn't affected by electromagnetic fields. We already have particles that don't interact with one or more forces. The weak interaction only affects fermions and antifermions. The strong force only affects quarks, photos are massless, etc. What's so hard to accept about a particle that doesn't interact with electromagnetism, and thus neither absorbs nor emits light?
The issue is not whether it acts like regular matter.
At issue is, rather, whether observations consistent with DM as formulated should be privileged over others that are not. Current behavior of cosmologists is that inconvenient observations should not count, and need not be paid any attention.
That is why the authors bring up sociological explanations for cosmologists' behavior. It is not scrupulous science.
At issue is, rather, whether observations consistent with DM as formulated should be privileged over others that are not. Current behavior of cosmologists is that inconvenient observations should not count, and need not be paid any attention.
That is why the authors bring up sociological explanations for cosmologists' behavior. It is not scrupulous science.
It's not hard to accept existence of dark matter, but it is an extremely flexible, hard to prove answer. If you see a galaxy that rotates differently, you say it has more or less dark matter. It sounds like an easy answer.
Not to forget that neutrinos also do not have an electric charge, i.e. also do not couple to photons directly.
There's probably more, I'm not up on all the particles. My thought is that a) a particle that only interacts with gravity is not prohibited by the Standard Model and b) our inability to detect (yet) such a particle is not proof it doesn't exist.
> a model universe in which the normal matter we see around us in the form of atoms makes up only 5% of all the energy in it. About 20% is made up of exotic dark matter particles
> for each gram of normal matter there are 25 grams of the exotic dark matter
20% is four times 5%, yet there is 25x difference in mass? How does that work?
> for each gram of normal matter there are 25 grams of the exotic dark matter
20% is four times 5%, yet there is 25x difference in mass? How does that work?
They are talking about dark matter in one instance, and dark matter + dark energy in the other. So, no contradiction.
Yeah the article seems to get some simple percentages wrong early on. (The downvotes on the comment above are incomprehensible, but that's downvotes for you.)
At this point, I consider "Dark Matter" to be a substitute for "Shit We Don't Know About". We know, roughly, how gravity and all these forces are supposed to behave.
Certain celestial bodies don't follow those rules according to what we know about both the rules and those bodies.
So there's something we don't know about there. Either the body or the rule is missing something. If it's the body, then there's a whole mess of matter that's just imperceptible to our current methods. It is "dark" to our observation.
Certain celestial bodies don't follow those rules according to what we know about both the rules and those bodies.
So there's something we don't know about there. Either the body or the rule is missing something. If it's the body, then there's a whole mess of matter that's just imperceptible to our current methods. It is "dark" to our observation.
Kind of smells like blackholes and we're pretty sure that they exist.
(Disclaimer: am particle physicist, but not a cosmologist) For a bit of context, see Sec. III.6 of https://arxiv.org/abs/2105.05208 ("Challenges for ΛCDM: An update", where ΛCDM is the "standard model of cosmology"). The linked article refers to _known_ problems that this model has describing small scale structures. That dark matter doesn't exists seems like a non-sequitur to me.
Can someone with an actual physics background clarify my understanding:
My interpretation of "dark matter" isn't that it's literally "matter" that is invisible and we are trying to find a way to detect it and interact with it.
Rather it's just a shorthand term that explains our math. We detect gravity. The only thing that we know that makes gravity is matter. We detect more gravity for the amount of matter we see. Therefore we call what we cannot detect "dark matter". But that's it. We have no other semblance that it is somehow "matter". We might as well call it "Unknown Gravity Generator".
Is that right or am I off base?
If I'm right, then could it just be as simple that gravity Works Differently at galactic scales much the same way that everything works differently at quantum scales and relativistic (ie high velocity) scales? And as such, we don't really need to "find" dark matter, but rather we just need to find out exactly under what circumstances the equations change - much as Einstein did for relativity? And it's a super hard problem because while we can make things move at the speed of light in a lab, we can't really give something galactic mass in a lab, and observing galactic-masses in the real world on a human scale is very hard as any relevant measurements would require multiple lifetimes to observe (hypothetically)
If I'm wrong, in what other ways is dark matter "matter-y" that makes it a useful term? And do scientists believe there is a chance we could actually be able to "generate" it an experimental environment?
My interpretation of "dark matter" isn't that it's literally "matter" that is invisible and we are trying to find a way to detect it and interact with it.
Rather it's just a shorthand term that explains our math. We detect gravity. The only thing that we know that makes gravity is matter. We detect more gravity for the amount of matter we see. Therefore we call what we cannot detect "dark matter". But that's it. We have no other semblance that it is somehow "matter". We might as well call it "Unknown Gravity Generator".
Is that right or am I off base?
If I'm right, then could it just be as simple that gravity Works Differently at galactic scales much the same way that everything works differently at quantum scales and relativistic (ie high velocity) scales? And as such, we don't really need to "find" dark matter, but rather we just need to find out exactly under what circumstances the equations change - much as Einstein did for relativity? And it's a super hard problem because while we can make things move at the speed of light in a lab, we can't really give something galactic mass in a lab, and observing galactic-masses in the real world on a human scale is very hard as any relevant measurements would require multiple lifetimes to observe (hypothetically)
If I'm wrong, in what other ways is dark matter "matter-y" that makes it a useful term? And do scientists believe there is a chance we could actually be able to "generate" it an experimental environment?
This theory is called MOND. It is generally considered to have fatal issues with observations:
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
> [how] is dark matter "matter-y" ... ?
Its characterizing bulk behaviour is that dark matter exerts a pressure on galaxies immersed in it, effectively squashing them inwards (or, if you like, preventing discoid galaxies from flying apart as they spin quickly).
Under <https://en.wikipedia.org/wiki/Dimensional_analysis>, pressure has dimension L^{-1}MT^{-2}, which is the same as energy-density.
Energy-density is encoded in the (symmetric, gauge-invariant, conserved, (0,2)) matter tensor of the Einstein Field Equations of General Relativity.
Among other things this preserves notions that matter/energy cannot be created or destroyed, only converted from one form to another.
It is the microscopic constitution of the bulk energy-density, and the details about how or if it can be converted into photons or some other radiation, or other types of matter, that is not known, although the bulk behaviour imposes numerous constraints.
As with all matter in General Relativity, dark matter is subject to the strong equivalence principle, just like laboratory Cavendish experiments, or binary or triple pulsar systems, or in galaxies' peculiar motions within galaxy clusters.
Finally, your "as simple that gravity Works Differently at galactic scales" is a rejection of the Strong Equivalence Principle, and also raises the question of the (unknown) microscopic details of how the inverse square law holds up so well everywhere except the edges of many known galaxies. Typical approaches involve a new long-range ("fifth") force that in bulk effectively applies a tension on the outer reaches of galaxies where MOND transitions from the familiar 1/r^2 inverse square law for gravity to the slower-decaying 1/r law. Tension has the dimensions of negative pressure, so essentially rather than outside-the-galaxy dark matter pushing the outer gas clouds and stars inwards, we have something inside the galaxy reaching out and pulling the same gas clouds and stars inwards. One is then left struggling to do anything other than to describe the microscopic behaviours of a field that sources this negative pressure, and making that field denser somewhere towards the middle of galaxies.
Its characterizing bulk behaviour is that dark matter exerts a pressure on galaxies immersed in it, effectively squashing them inwards (or, if you like, preventing discoid galaxies from flying apart as they spin quickly).
Under <https://en.wikipedia.org/wiki/Dimensional_analysis>, pressure has dimension L^{-1}MT^{-2}, which is the same as energy-density.
Energy-density is encoded in the (symmetric, gauge-invariant, conserved, (0,2)) matter tensor of the Einstein Field Equations of General Relativity.
Among other things this preserves notions that matter/energy cannot be created or destroyed, only converted from one form to another.
It is the microscopic constitution of the bulk energy-density, and the details about how or if it can be converted into photons or some other radiation, or other types of matter, that is not known, although the bulk behaviour imposes numerous constraints.
As with all matter in General Relativity, dark matter is subject to the strong equivalence principle, just like laboratory Cavendish experiments, or binary or triple pulsar systems, or in galaxies' peculiar motions within galaxy clusters.
Finally, your "as simple that gravity Works Differently at galactic scales" is a rejection of the Strong Equivalence Principle, and also raises the question of the (unknown) microscopic details of how the inverse square law holds up so well everywhere except the edges of many known galaxies. Typical approaches involve a new long-range ("fifth") force that in bulk effectively applies a tension on the outer reaches of galaxies where MOND transitions from the familiar 1/r^2 inverse square law for gravity to the slower-decaying 1/r law. Tension has the dimensions of negative pressure, so essentially rather than outside-the-galaxy dark matter pushing the outer gas clouds and stars inwards, we have something inside the galaxy reaching out and pulling the same gas clouds and stars inwards. One is then left struggling to do anything other than to describe the microscopic behaviours of a field that sources this negative pressure, and making that field denser somewhere towards the middle of galaxies.
Well, to some approximation, in general relativity, matter=gravity generator. (And dark=not interacting with photons enough that we can see it)
Only 30 years ago we had never seen a brown dwarf, even though its existence had been theorized much earlier. There are not enough brown dwarfs to account for the missing mass in the universe, but is it at all possible that some other type of body that we have not yet seen could account for it? Or is the requirement that dark matter be non-baryonic a fundamental requirement of the theory?
IANAP. AFAIK, Large massive bodies (MACHOS) have been ruled out by observation, and baryons would be detectable through EM.
How do the recently discovered rare galaxies that look like they have no dark matter fit in with the idea that instead of clumpy stuff that can end up distributed oddly, we're dealing with a universal physical law? Shouldn't the physical law be the same for all galaxies?
I'm no physicist but if you want to be cheeky, you introduce a "rare dark matter" to a MOND model and explain away those rare instances.
My point is, dark matter explains the observations by being very flexible. There can be any amount of dark matter to fit the observations.
My point is, dark matter explains the observations by being very flexible. There can be any amount of dark matter to fit the observations.
All the celestial bodies that make up the system are in free fall (acceleration) toward the center of the system.
Gravity is the action that tries to maintain a defined acceleration towards the gravity source according to the distance from the gravity source.
Therefore, if the gravity source accelerates, the gravitational action should be considered different from when the gravity source is stationary.
Sciama named this action "inertial induction" and proposed it.
All the stars that make up the galaxy are in free fall (acceleration) toward the center of the galaxy. Current calculation methods do not take this fact into account at all.
There is no way that the observation can be explained by a calculation method that ignores the facts.
I have written a paper* on how the inertial induction of stars works in galaxies.
*N. Namba, "Stellar movement in the galaxy explained by inertial induction", Phys. Essays 15, 156(2002)
In addition, I mentioned the essence of gravity and inertia in a 2014 paper, showing that the existing theory of gravity is incomplete. The full text of this paper is now available on GALE ACADEMIC ONE FILE. Please see attached.
https://go.gale.com/ps/i.do?p=AONE&u=googlescholar&id=GALE|A...
*N. Namba, "Stellar movement in the galaxy explained by inertial induction", Phys. Essays 15, 156(2002)
In addition, I mentioned the essence of gravity and inertia in a 2014 paper, showing that the existing theory of gravity is incomplete. The full text of this paper is now available on GALE ACADEMIC ONE FILE. Please see attached.
https://go.gale.com/ps/i.do?p=AONE&u=googlescholar&id=GALE|A...
It is true that it has never been observed and is hypothetical.
However, we have observations which break the rules. https://en.wikipedia.org/wiki/Galaxy_rotation_curve
The thing to me, why do we assume kepler's law applies to galaxies? It has only been proven in relation to the solar system. Perhaps it has been proven to work for the exoplanets in other systems?
Also what exactly is dark matter? Is it some exotic unproven god or is it just dust, hydrogen that just doesnt glow or light up?
What about our observations are just wrong? What if we haven't adjusted our observations for https://en.wikipedia.org/wiki/Local_Interstellar_Cloud and thusly we are slightly off because of some latent glow from the local cloud? Or perhaps even going further and being in some transition to the neighbour cloud is throwing observations off.
However, we have observations which break the rules. https://en.wikipedia.org/wiki/Galaxy_rotation_curve
The thing to me, why do we assume kepler's law applies to galaxies? It has only been proven in relation to the solar system. Perhaps it has been proven to work for the exoplanets in other systems?
Also what exactly is dark matter? Is it some exotic unproven god or is it just dust, hydrogen that just doesnt glow or light up?
What about our observations are just wrong? What if we haven't adjusted our observations for https://en.wikipedia.org/wiki/Local_Interstellar_Cloud and thusly we are slightly off because of some latent glow from the local cloud? Or perhaps even going further and being in some transition to the neighbour cloud is throwing observations off.
There are multiple independent lines of evidence for DM. Your questions would be answered by reading the Wikipedia article on Dark Matter:
https://en.wikipedia.org/wiki/Dark_matter
https://en.wikipedia.org/wiki/Dark_matter
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe.[1]
We dont have the answers for anything here.
We dont have the answers for anything here.
> We dont have the answers for anything here.
This very clearly must hold true for any "we" which refuses to read past the first line of an encyclopedia article.
This very clearly must hold true for any "we" which refuses to read past the first line of an encyclopedia article.
This article is not very good. It conflates disproving specific models that use dark matter with disproving dark matter itself.
I would place this comment in the same bucket :P
You can't "prove" that something doesn't exist. And dark matter is simply a big fat "????" inserted into our math to make our equations match what we see.
I think it's fair for them to state that dark matter doesn't exist, in the same way that I can fairly confidently state that "The christian god" does not exist.
Doesn't explain how we got here, or what actually needs to change to make our equations match our observations, but it's a reasonable stance to encourage folks to stop spending time on an unlikely solution (even if it so far produces the best model we have).
You can't "prove" that something doesn't exist. And dark matter is simply a big fat "????" inserted into our math to make our equations match what we see.
I think it's fair for them to state that dark matter doesn't exist, in the same way that I can fairly confidently state that "The christian god" does not exist.
Doesn't explain how we got here, or what actually needs to change to make our equations match our observations, but it's a reasonable stance to encourage folks to stop spending time on an unlikely solution (even if it so far produces the best model we have).
Dark matter isn't a mathematical invention, it is directly observed: the visible matter of galaxies and the bulk of their gravitational mass can be in different places.
Any attempt to "disprove" dark matter that doesn't address the hard observational fact that gravitational mass and visible mass are separable is invalid.
https://www.wikiwand.com/en/Bullet_Cluster
Any attempt to "disprove" dark matter that doesn't address the hard observational fact that gravitational mass and visible mass are separable is invalid.
https://www.wikiwand.com/en/Bullet_Cluster
I really don't think we're disagreeing.
You're just saying, very clearly: Our observational data does not match our mathematical models for gravity, and our alternative models don't account for this case (bullet cluster)
I'm not disagreeing with you, and I'm not proposing MOND or derivatives are a valid solution, I'm just saying that you're still just positing:
"we saw thing X that doesn't work with our current model, or with our modified model, so there must be some mysterious "dark" matter that we have to add to bring our math back to matching what we observe."
So far, though - no experiment to actually find or record it, or make valid guesses about how or why it's distributed from a theoretical view, rather than as "glue" to hold our model back together, has been found (at least that I'm aware of).
So I guess I am disagreeing - It's not "directly observed" in any sense other than "something is wrong here and we can't explain why".
You're just saying, very clearly: Our observational data does not match our mathematical models for gravity, and our alternative models don't account for this case (bullet cluster)
I'm not disagreeing with you, and I'm not proposing MOND or derivatives are a valid solution, I'm just saying that you're still just positing:
"we saw thing X that doesn't work with our current model, or with our modified model, so there must be some mysterious "dark" matter that we have to add to bring our math back to matching what we observe."
So far, though - no experiment to actually find or record it, or make valid guesses about how or why it's distributed from a theoretical view, rather than as "glue" to hold our model back together, has been found (at least that I'm aware of).
So I guess I am disagreeing - It's not "directly observed" in any sense other than "something is wrong here and we can't explain why".
The "something" that "is wrong here" though is not merely a mathematical inconsistency in the amount of force or speed you expect. That may have been true when dark matter was first proposed as a solution for the weird spinning behavior of galaxies in 1933, but not so any more.
Dark matter is an actual physical reality that you can see with your normal human eyeballs in a photograph. The light emitting stuff is in one part of the picture, and the gravity causing stuff is in another part of the picture. You can see it with your own eyes. The bulk of the gravity of galaxies is separable from the bulk of its visible matter.
Dark Matter is the class of hypotheses that explains this plain observational reality by supposing some kind of invisible matter, which is the only explanation that fits what the photographs show.
Any attempt to discredit it must be accompanied with an alternative explanation of how the gravitational mass of galaxies seems to be removable from their visible material.
This article is like denying that the sun exists, without positing an alternative for where daylight comes from.
Dark matter is an actual physical reality that you can see with your normal human eyeballs in a photograph. The light emitting stuff is in one part of the picture, and the gravity causing stuff is in another part of the picture. You can see it with your own eyes. The bulk of the gravity of galaxies is separable from the bulk of its visible matter.
Dark Matter is the class of hypotheses that explains this plain observational reality by supposing some kind of invisible matter, which is the only explanation that fits what the photographs show.
Any attempt to discredit it must be accompanied with an alternative explanation of how the gravitational mass of galaxies seems to be removable from their visible material.
This article is like denying that the sun exists, without positing an alternative for where daylight comes from.
> It's not "directly observed" in any sense other than "something is wrong here and we can't explain why".
That's not disagreeing, that's literally an observation, in this case via photons coming from things we can see possibly interacting with things we can't. That's as direct an observation as you're going to get for most things in the universe.
That's not disagreeing, that's literally an observation, in this case via photons coming from things we can see possibly interacting with things we can't. That's as direct an observation as you're going to get for most things in the universe.
> That's as direct an observation as you're going to get for most things in the universe.
It is decidedly not. It's a clear sign that points at "Our models don't work well here", but simply noting that we're seeing an unexpected result is FAR different than being able to declare "we have observed dark matter".
Basically - if you're saying that the bullet cluster is good evidence against MOND, welp... we agree.
If you're saying the bullet cluster is direct observation of dark matter... I don't agree at all. It's just proof that both models are broken for the cases where we see galactic collisions. The fact that you can wallpaper over this in models with dark matter is... the point of dark matter in the first place: A handy escape hatch for cases like this.
It is decidedly not. It's a clear sign that points at "Our models don't work well here", but simply noting that we're seeing an unexpected result is FAR different than being able to declare "we have observed dark matter".
Basically - if you're saying that the bullet cluster is good evidence against MOND, welp... we agree.
If you're saying the bullet cluster is direct observation of dark matter... I don't agree at all. It's just proof that both models are broken for the cases where we see galactic collisions. The fact that you can wallpaper over this in models with dark matter is... the point of dark matter in the first place: A handy escape hatch for cases like this.
>an unlikely solution (even if it so far produces the best model we have).
If it is consistently producing the best model, why is it an unlikely solution?
What would be more likely than the model which produces the best match to what we observe?
If it is consistently producing the best model, why is it an unlikely solution?
What would be more likely than the model which produces the best match to what we observe?
Well - I would say this article is trying to discuss why it would be unlikely -
Namely, most of the experiments we can find to experimentally test for dark matter fail.
Just because a model fits our current data doesn't make it correct (honestly - my strong stance is no model is correct, but some models are useful, and some more useful than others).
Epicycles were a fantastic explanation for the timing and movements of planets appearing in the sky - They were the best model we had for hundreds of years, but the model was also utterly incorrect.
It wasn't until an almost rock solid assumption (that earth was the center of everything) was assaulted by Copernicus that we developed much more robust models.
I find it fairly interesting that epicycles were also an attempt to explain a observational data that was very hard to fit into current models. There's a fairly straight parallel to dark matter here.
I find it very compelling that we have a foundational assumption in our current model that isn't true, and that's why we're offsetting everything with dark matter to make the math line back up with reality.
Namely, most of the experiments we can find to experimentally test for dark matter fail.
Just because a model fits our current data doesn't make it correct (honestly - my strong stance is no model is correct, but some models are useful, and some more useful than others).
Epicycles were a fantastic explanation for the timing and movements of planets appearing in the sky - They were the best model we had for hundreds of years, but the model was also utterly incorrect.
It wasn't until an almost rock solid assumption (that earth was the center of everything) was assaulted by Copernicus that we developed much more robust models.
I find it fairly interesting that epicycles were also an attempt to explain a observational data that was very hard to fit into current models. There's a fairly straight parallel to dark matter here.
I find it very compelling that we have a foundational assumption in our current model that isn't true, and that's why we're offsetting everything with dark matter to make the math line back up with reality.
I understand what you're saying, despite not necessarily agreeing with everything you are saying.
It's just really odd to say:
"X produces the best model we have"
But also say:
"X is an unlikely solution".
If it produces the best model we have, it's the most likely solution at this time. That doesn't guarantee it will ultimately be the correct solution, sure.
It's just really odd to say:
"X produces the best model we have"
But also say:
"X is an unlikely solution".
If it produces the best model we have, it's the most likely solution at this time. That doesn't guarantee it will ultimately be the correct solution, sure.
Totally fair. But we're in that weird spot where we've been trying to find a concrete example of dark matter (testable hypothesis that would apply) and so far we're not coming up all that hot.
So I guess "unlikely" is probably too strong even in my opinion. I just think it hints that we have a structural problem in the house, and continuing to add wall paper is probably not going to fix the issue, we need a shift in understanding somewhere else.
So I guess "unlikely" is probably too strong even in my opinion. I just think it hints that we have a structural problem in the house, and continuing to add wall paper is probably not going to fix the issue, we need a shift in understanding somewhere else.
> You can't "prove" that something doesn't exist
You could definitely prove that something doesn't exist in any meaningful quantity. Happens all the time: The experiments searching for new particles end up proving that if they do exist, they interact too weakly to be detectable. Similarly you could make observations which place an upper bound on the dark matter density, possibly low enough that it cannot explain the galaxy rotation curves etc. anymore.
You could definitely prove that something doesn't exist in any meaningful quantity. Happens all the time: The experiments searching for new particles end up proving that if they do exist, they interact too weakly to be detectable. Similarly you could make observations which place an upper bound on the dark matter density, possibly low enough that it cannot explain the galaxy rotation curves etc. anymore.
Does a number exist that's greater than 2 but smaller than 1?
yes... :P https://imgur.com/a/gAU89Qc
that 3 is greater in value than the number 2, yet smaller in size than the number 1.
But more seriously - you're conflating a mathematical model with the reality we're observing. Our number systems (all the varieties of math) are subject to foundational contradictions and paradoxes, and proofs within them can be incredible tools - but they are not objective truths.
We assume that the universe we experience and model is the same as the universe far, FAR away - and that's a reasonable and logical assumption - but it's STILL an assumption.
that 3 is greater in value than the number 2, yet smaller in size than the number 1.
But more seriously - you're conflating a mathematical model with the reality we're observing. Our number systems (all the varieties of math) are subject to foundational contradictions and paradoxes, and proofs within them can be incredible tools - but they are not objective truths.
We assume that the universe we experience and model is the same as the universe far, FAR away - and that's a reasonable and logical assumption - but it's STILL an assumption.
You didn't distinguish between model or reality you just wrote you can't "prove" that something does not exist.
And even in reality you can disprove things, you just need to define the environment. You can't disprove non existence in reality things universally and at all times.
And even in reality you can disprove things, you just need to define the environment. You can't disprove non existence in reality things universally and at all times.
Good reply btw
What if most of the dark matter surrounding an object is moving in more or less the same direction at the same velocity, being in the same neighborhood?
The Chandrasekhar-friction-based objection to dark matter seems to assume that dark matter must be a kind of soup that is standing still, while only the galaxies (or whatever objects) wade through it.
The Chandrasekhar-friction-based objection to dark matter seems to assume that dark matter must be a kind of soup that is standing still, while only the galaxies (or whatever objects) wade through it.
If it had the same distribution as visible matter, it wouldn't be "dark". There would just more matter. It is that it is not doing the same as visible matter that makes it useful to patch in for otherwise inconvenient observations.
Dark Matter advocates, if honest, should be trying to patch up their definition to account for all these observations. Studiously ignoring them is unscrupulous.
Dark Matter advocates, if honest, should be trying to patch up their definition to account for all these observations. Studiously ignoring them is unscrupulous.
I have a hard time imagine the shape of dark-matter. What does that look like, a particle iceberg squeezed into a hidden dimension that surrounds all things? Like a Neutrino that does not travell, but instead waves like seaweed?
How does it look in 3dimensional terms?
As a lay person on this topic, a question. I've always heard that string theory was an untestable theory that academia was obsessed with for decades, and research on it soaked up a large amount of academic budgets and grant money. And was ultimately fruitless. (Again, I'm on the outside looking in, I don't work in the field so I'm not 100% sure if this is accurate)
Is dark matter in the same boat as string theory was, from a grant money and research standpoint?
Is dark matter in the same boat as string theory was, from a grant money and research standpoint?
> Again, I'm on the outside looking in, I don't work in the field so I'm not 100% sure if this is accurate
It's not. Point by point:
> I've always heard that string theory was an untestable theory
True in a certain light, but misleading. Any theory of quantum gravity is going to be untestable with current methods: the relevant energy scales are just too high. That doesn't mean they won't ever be testable. We might figure out a qualitatively better collider design, or find a way to get useful data from astronomical observations, or find some other clever way around the problem. Or we might not. Theorists would love to have more experimental evidence to work with - but wanting doesn't make it so.
A somewhat more legitimate concern is the size of the "string landscape": (perturbative) string theory permits many, many, many different possible values for different physical constants. It's likely, but not certain, that this is also true nonperturbatively. If so, then we can't use the measured values of those constants as evidence for or against string theory. This is unfortunate, but hardly unique: the standard model, after all, permits infinitely many such possibilities.
> and research on it soaked up a large amount of academic budgets and grant money
Not really. Most physics funding goes to applied research, most pure research funding is for experimental work, and the majority of theory funding is not for high energy theory. I don't know whether most high energy theory grants go to string theorists: it's possible.
> And was ultimately fruitless
Only insofar as all work on quantum gravity has been "fruitless".
It's not. Point by point:
> I've always heard that string theory was an untestable theory
True in a certain light, but misleading. Any theory of quantum gravity is going to be untestable with current methods: the relevant energy scales are just too high. That doesn't mean they won't ever be testable. We might figure out a qualitatively better collider design, or find a way to get useful data from astronomical observations, or find some other clever way around the problem. Or we might not. Theorists would love to have more experimental evidence to work with - but wanting doesn't make it so.
A somewhat more legitimate concern is the size of the "string landscape": (perturbative) string theory permits many, many, many different possible values for different physical constants. It's likely, but not certain, that this is also true nonperturbatively. If so, then we can't use the measured values of those constants as evidence for or against string theory. This is unfortunate, but hardly unique: the standard model, after all, permits infinitely many such possibilities.
> and research on it soaked up a large amount of academic budgets and grant money
Not really. Most physics funding goes to applied research, most pure research funding is for experimental work, and the majority of theory funding is not for high energy theory. I don't know whether most high energy theory grants go to string theorists: it's possible.
> And was ultimately fruitless
Only insofar as all work on quantum gravity has been "fruitless".
There's been concrete expirements looking for dark matter (not yet found). That advances science, even if unfruitful.
I don't think there have been any expirements re: strings? So it advances philosophy, but not really science yet.
I don't think there have been any expirements re: strings? So it advances philosophy, but not really science yet.
That's interesting. Good to know.
It's amazing that even theoretical physicists are coerced into believing in superstition by mathematics.
I landed on the page and there doesn’t seem to be an article or a “pay/register to view” prompt. Just the title, the hero image, a word count, and some comments (which prompts to register to add comments)
Does it load for others?
Does it load for others?
[deleted]
Stupid person here. Couldn't DM just be like gauge bosons (no mass) and also not carry any other force that would "slow down" other matter?
Needs mass -- that's what couples to gravitation, and that's the original reason we think there is DM.
Big claim, one test (based on their model(, fails to explain gravitational lensing phenomena without a terra centric set of spinning wheels in theory...
I've had this theory for a long time that maybe the missing mass that dark matter is supposed to account for is actually antimatter (which also should theoretically exist in equal quantities to matter), due to antimatter actually having antigravity, and therefore dispersing thinly throughout space rather than clumping together.
Can someone knowledgeable in physics set me straight on the plausibility of this theory?
Can someone knowledgeable in physics set me straight on the plausibility of this theory?
Antimatter isn't dark. It interacts with matter just fine -- too fine!
I am not knowledgeable in physics, but I think dark matter is supposed to be unaffected by electromagnetic forces (hence why it can't be seen) which is definitely not true for antimatter.
I'd really either like someone to find a new dark matter particle or to fix most of the problems with MOND.
Armchairing here, but what exactly about Einstein's theory doesn't correspond with this so called "current cosmological model"? This article doesn't really state what, exactly, needs to be "revised". Because, as someone said farther up in the comments, as far as I know, Einstein's theory has been confirmed against every experiement ever done.
Confirmed against every experiment, but not observation. We do not know why galaxies rotate at the speed they do. Apparently we have a pretty good idea of their visible mass, but should result in much slower galaxies than what we observe.
And then how do we know we have an accurate estimation of a stellar object’s mass if the observations don’t match our predictions? This is a big question for me.
Ok, I wasn't being very accurate. More correctly, we do not know why outer stars in the galaxy rotate at the same speed as inner stars. As per gravitation laws, the farther the star is, the slower it should rotate. But they all rotate at the same speed, which only adds up if you assume there is some "dark matter" around the outside of the galaxy.
I honestly do not know how they estimate stellar masses. I suspect they just look at density of stars and have perhaps established that stars are more or less distributed randomly, but I'm armchairing here. Maybe an expert can chime in.
I honestly do not know how they estimate stellar masses. I suspect they just look at density of stars and have perhaps established that stars are more or less distributed randomly, but I'm armchairing here. Maybe an expert can chime in.
>As per gravitation laws, the farther the star is, the slower it should rotate.
That depends. The 1/R orbital speed relationship is valid only in cases of spherically symmetric mass distribution or when the radiuses of the interacting masses being much smaller than the distance between them. Neither of these is true for a star inside a galaxy disk. Correctly accounting for the disk shape gives you expected orbital speed much closer to the "outer stars in the galaxy rotate at the same speed as inner stars", though not exactly equal. The remaining difference is explained by the seond factor.
That second factor is that "rotate" i suppose means orbiting around galaxy center. The stars in the disk aren't really orbiting, ie. they are actually flying away like in a fireworks wheel as the galaxy disk becomes larger and thinner - exactly because the stars' speed is still somewhat higher than the orbital speed as calculated above. Thus no need for DM here.
That depends. The 1/R orbital speed relationship is valid only in cases of spherically symmetric mass distribution or when the radiuses of the interacting masses being much smaller than the distance between them. Neither of these is true for a star inside a galaxy disk. Correctly accounting for the disk shape gives you expected orbital speed much closer to the "outer stars in the galaxy rotate at the same speed as inner stars", though not exactly equal. The remaining difference is explained by the seond factor.
That second factor is that "rotate" i suppose means orbiting around galaxy center. The stars in the disk aren't really orbiting, ie. they are actually flying away like in a fireworks wheel as the galaxy disk becomes larger and thinner - exactly because the stars' speed is still somewhat higher than the orbital speed as calculated above. Thus no need for DM here.
Isn't that question why they felt the need to add "dark matter" to the equation? "Our mass estimation must be wrong, therefore there's all this mass we're not seeing"
They had to add more matter in some places and less in others. Estimation would have wrong numbers all around.
Also armchair, but this is how I understand it: if you take gravitation as it is typically understood, it implies motion of stars around galaxies which we don't see. The discrepancy can be accounted for if you assume there is 33% more mass than we can traditionally observe, roughly suffusing each galaxy. Since we can't observe it, it's believed to not interact with any normal matter other than through the gravitational field.
edit: 33% is definitely wrong, but I don't know the actual number...
edit: 33% is definitely wrong, but I don't know the actual number...
On galactic and larger scales galaxies move and form as though there is a lot more mass out there than we can see. I forget the exact figure but something like 20x as much.
Either you have to patch your gravity theory or assume there’s a bunch of stuff which interacts gravitationally but barely or not at all with electromagnetism.
Either you have to patch your gravity theory or assume there’s a bunch of stuff which interacts gravitationally but barely or not at all with electromagnetism.
Has this observation been tested against frame dragging? What if supermassive black holes rotate much faster than we except?
I'm sure that every iteration of "have you tried X" has been tried, which is why the most popular theory is "there's a bunch of stuff we can only see through its gravitational effect".
Central black holes' spins don't drive their host galaxies' rotation.
* Elliptical galaxies exist where the rotation curve almost exclusively measures radial motion of blobs of gas (radiating specific wavelengths, whose redshift we can compare with other parts of the same galaxy), and sometimes other bright objects with characteristic spectra, which move outwards and inwards on an elliptical orbit; these galaxies may not spin around an axis, and may not even have anything like an equator. The anomaly is that the difference in these rising-and-falling orbits' is not as large as expected -- the outer reaches are dimmer, less dusty, and less gassy than the denser inner reaches, so there is less ordinary mass out there, but this reduction in mass density is not reflected in the orbital speeds;
* In discoid galaxies (spirals, etc.), the spin-axis of the central black hole may point at any angle relative to an axis through the galaxy centre, perpendicular to the thin disc; the polar jets of black holes can even blast mostly into the thin disc, rather than mostly out of it; the polar jets are indicative of the spin-axis of the central black hole;
* Galaxies may have more than one central black hole, especially the larger ellipticals. These central black holes typically do not have their spin axes point in the same direction, and where the spin axes are remotely close to perpendicular the black holes might not all spin in the same direction;
* Some central black holes are gargantuan, some are petite (ours is small, especially compared to the number of stars in the Milky Way), and some are apparently absent, but the rotation-curve anomalies appear to be very similar nevertheless.
That said, active central black holes -- "Active Galactic Nuclei" (AGN), of which quasars are a species -- can blow tremendous amounts of matter out of the central regions of their host galaxies, and that can alter the orbital speeds of gas and dust clouds in those galaxies generally, and much more so the behaviours of X-ray-bright gas and dust they shoot outwards into extragalactic space. AGNs can switch from very bright to essentially off, and as far as we can tell the switch-off of AGNs does not cause the rotation curve anomalies to relax. (Our extremely quiet central black hole may have been an AGN perhaps as recently as millions of years ago. <https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-r...>).
Frame dragging by the rotation of central black holes in AGNs may be seen in the corkscrewing of their jet emissions: Galaxy 3C 348 shows this clearly <https://duckduckgo.com/?q=3C+348+galaxy&iax=images&ia=images...> as does the more popular M87 <https://apod.nasa.gov/apod/ap011101.html>
These jets are very bright in some characteristic wavelengths (radio in 3C 348, X-Rays in M87), but they're much sparser than the starry regions of their respective galaxies. These two galaxies are large ellipticals, and their jets do not align with anything like a central rotational axis as in a spiral galaxy.
The screw displacement related to frame dragging happens in the near region to the source black holes. Anomalous gas-cloud rotation curves are found in the far region, at the outer edges of galaxies.
* Elliptical galaxies exist where the rotation curve almost exclusively measures radial motion of blobs of gas (radiating specific wavelengths, whose redshift we can compare with other parts of the same galaxy), and sometimes other bright objects with characteristic spectra, which move outwards and inwards on an elliptical orbit; these galaxies may not spin around an axis, and may not even have anything like an equator. The anomaly is that the difference in these rising-and-falling orbits' is not as large as expected -- the outer reaches are dimmer, less dusty, and less gassy than the denser inner reaches, so there is less ordinary mass out there, but this reduction in mass density is not reflected in the orbital speeds;
* In discoid galaxies (spirals, etc.), the spin-axis of the central black hole may point at any angle relative to an axis through the galaxy centre, perpendicular to the thin disc; the polar jets of black holes can even blast mostly into the thin disc, rather than mostly out of it; the polar jets are indicative of the spin-axis of the central black hole;
* Galaxies may have more than one central black hole, especially the larger ellipticals. These central black holes typically do not have their spin axes point in the same direction, and where the spin axes are remotely close to perpendicular the black holes might not all spin in the same direction;
* Some central black holes are gargantuan, some are petite (ours is small, especially compared to the number of stars in the Milky Way), and some are apparently absent, but the rotation-curve anomalies appear to be very similar nevertheless.
That said, active central black holes -- "Active Galactic Nuclei" (AGN), of which quasars are a species -- can blow tremendous amounts of matter out of the central regions of their host galaxies, and that can alter the orbital speeds of gas and dust clouds in those galaxies generally, and much more so the behaviours of X-ray-bright gas and dust they shoot outwards into extragalactic space. AGNs can switch from very bright to essentially off, and as far as we can tell the switch-off of AGNs does not cause the rotation curve anomalies to relax. (Our extremely quiet central black hole may have been an AGN perhaps as recently as millions of years ago. <https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-r...>).
Frame dragging by the rotation of central black holes in AGNs may be seen in the corkscrewing of their jet emissions: Galaxy 3C 348 shows this clearly <https://duckduckgo.com/?q=3C+348+galaxy&iax=images&ia=images...> as does the more popular M87 <https://apod.nasa.gov/apod/ap011101.html>
These jets are very bright in some characteristic wavelengths (radio in 3C 348, X-Rays in M87), but they're much sparser than the starry regions of their respective galaxies. These two galaxies are large ellipticals, and their jets do not align with anything like a central rotational axis as in a spiral galaxy.
The screw displacement related to frame dragging happens in the near region to the source black holes. Anomalous gas-cloud rotation curves are found in the far region, at the outer edges of galaxies.
Germans … always be party pooping. Let us have fun, we don’t always need to be correct.
I'm extremely skeptical of a 'simple test' which proclaims to overturn decades of scientific knowledge. Why did it take until 2022 for someone to think of this, and not a hungry grad student in the 80s looking to make a name for themselves?
As @greenthrow notes, Modified Newtonian Dynamics has been around since the early 80s, first proposed by Milgrom.
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
It seems like the article has cause-and-effect reversed. Dark matter is a result of noticing some problems with the mathematics according to observations, and trying to introduce extra terms that make the equations balance. Nobody just inserted a lot of extra complexity into the model, then hoped they could twist the experiments to justify it. People have known that this isn't entirely satisfying as a solution.
Otherwise, the article actually seems a surprisingly reasonable complaint about being hard to get funding for trying to develop better alternative models which explain observations better.
Otherwise, the article actually seems a surprisingly reasonable complaint about being hard to get funding for trying to develop better alternative models which explain observations better.
the article actually seems a surprisingly reasonable complaint about being hard to get funding for trying to develop better alternative models which explain observations better
But let's be careful to not overgeneralize here. The author is working out of Bonn, Germany. I have no idea how German research gets funded or what their priorities are. More importantly, I have no idea for how that funding model compares with the funding model being used by other countries. All I can reasonably ascertain after reading this article is Germany isn't funding research to develop better alternative models. I have no knowledge for what other countries are funding.
But let's be careful to not overgeneralize here. The author is working out of Bonn, Germany. I have no idea how German research gets funded or what their priorities are. More importantly, I have no idea for how that funding model compares with the funding model being used by other countries. All I can reasonably ascertain after reading this article is Germany isn't funding research to develop better alternative models. I have no knowledge for what other countries are funding.
Well think of newtonian physics. For things humans experience, it's generally plenty. Running, walking, flying, shooting bullets, etc work just fine. Sure lasers, satellites, fission/fusion, astronomy, etc start breaking things.
Gravity is damn near perfect on the scale of the solar system. A huge number of zeros of precision, makes great prediction, etc. Even blackholes (which is quite the corner case) seems fine with the current theory of gravity until you get down into the small details and the search for a grand unification of quantum and relativity.
However as the scale of a galaxy things break down. So there's at least 2 possibilities. One that the theory of gravity is wrong at large scales, or there's something else involved, like dark matter.
Seems natural that scientist have a working assumption that the theory of gravity is right, but the problems with it are getting more attention. There's not just one competing theory for the next step for gravity.
Gravity is damn near perfect on the scale of the solar system. A huge number of zeros of precision, makes great prediction, etc. Even blackholes (which is quite the corner case) seems fine with the current theory of gravity until you get down into the small details and the search for a grand unification of quantum and relativity.
However as the scale of a galaxy things break down. So there's at least 2 possibilities. One that the theory of gravity is wrong at large scales, or there's something else involved, like dark matter.
Seems natural that scientist have a working assumption that the theory of gravity is right, but the problems with it are getting more attention. There's not just one competing theory for the next step for gravity.
Read the article. It isn't a new claim.
So why isn't hasn't it been accepted long ago?
Think of it as being more like an anti-crime editorial than a scientific argument. The argument is about budgetary priorities and complaining about other physicists.
Because it fails to account for all DM observations.
[deleted]
The statement "phlogiston doesn't exist", by itself, also doesn't acccount for all observations for which phlogiston adherents require the existence phlogiston.
This is a low-brow dismissal without basis in fact. At the moment, multiple independent lines of evidence suggest that DM is real. There are no observations which contradict DM. Any competing theory must explain the same observations, which means that it will necessarily be a theory of dark matter. Dark matter is a real phenomenon, whether or not you choose to acknowledge its reality.
Dark matter isn't scientific or knowledge, its a cludge factor to make the equations match the observations and it's never been observed ever.
It is definitely a scientific model. It posits that
(1) the observed differences in gravitational forces come from a gravitational field source, not modified equations themselves
(2) The field sources are a form of matter, thus obeying some "obvious" laws like mass conservation
(3) The new kind of matter is also attracted by gravity itself, which even allows for limited predictions of how its mass distribution behaves
And we can only say it's never been observed directly, because there is indeed enough indirect evidence pointing towards its existence.
(1) the observed differences in gravitational forces come from a gravitational field source, not modified equations themselves
(2) The field sources are a form of matter, thus obeying some "obvious" laws like mass conservation
(3) The new kind of matter is also attracted by gravity itself, which even allows for limited predictions of how its mass distribution behaves
And we can only say it's never been observed directly, because there is indeed enough indirect evidence pointing towards its existence.
> The implications of this are nothing short of a revision of Einstein’s theory of gravitation. Why the scientific community is in denial about the falsification of the dark matter model (...)
This is easy to explain. For Einstein's theory of gravitation you have the experimental evidence of every experiment every done, and against you have one guy with a half-baked argument.
This is easy to explain. For Einstein's theory of gravitation you have the experimental evidence of every experiment every done, and against you have one guy with a half-baked argument.
Plus accusing the mainstream scientific community of "blindly and religiously believing in [...]" is a page taken directly from the Crackpot Index [1].
"They are suppressing my work!"
"They do not want you to read this!"
Etc.
[1] https://math.ucr.edu/home/baez/crackpot.html
"They are suppressing my work!"
"They do not want you to read this!"
Etc.
[1] https://math.ucr.edu/home/baez/crackpot.html
That's a pretty fun index. If you removed the bias of accepting the current cosmological model as consensus and read it like it was submitted by a grad student how many points would the dark matter & dark energy model accrue? Is it logically consistent to propose a model that requires such a large adjustment by the inclusion of variables that have never been experimentally proven to exist? Does this model rest on the laurels and works of Albert Einstein? "10 points for each new term you invent and use without properly defining it." Do dark matter and dark energy not qualify here?
IANAP (physicist) but using this index it's hard not to imagine another place in the multiverse where this dark energy/matter cosmological model receives a high score on this rubric.
IANAP (physicist) but using this index it's hard not to imagine another place in the multiverse where this dark energy/matter cosmological model receives a high score on this rubric.
Well, the Crackpot Index is obviously tongue in cheek, but also born out of frustration, I think. It must get tiresome for scientists to listen to cranks trying to "disprove" established science with bizarre theories and a complete disregard for the literature. You can address one, two, three of these people, but it soon becomes a bother and you're tempted to write the Index instead.
I agree it's probably very difficult to tell really novel and paradigm-shifting theories from the ramblings of cranks.
I suppose the Dark Matter model scores highly in some items of the Crackpot Index but very low in "the government is trying to suppress this", "everything they told you is a lie", and also the scientists who proposed it understood the established science and didn't randomly disregard it. I think the "conspiracy" aspect is what sets a crackpot apart.
Again, it's possible that a person is a crackpot AND he/she is also right about a particular theory!
I agree it's probably very difficult to tell really novel and paradigm-shifting theories from the ramblings of cranks.
I suppose the Dark Matter model scores highly in some items of the Crackpot Index but very low in "the government is trying to suppress this", "everything they told you is a lie", and also the scientists who proposed it understood the established science and didn't randomly disregard it. I think the "conspiracy" aspect is what sets a crackpot apart.
Again, it's possible that a person is a crackpot AND he/she is also right about a particular theory!
> Again, it's possible that a person is a crackpot AND he/she is also right about a particular theory!
We call that the Crackpot Jackpot.
We call that the Crackpot Jackpot.
> every experiment ever done
But that is manifestly untrue. If every experiment confirmed Einstein we would not even be talking about dark matter.
> one guy with a half-baked argument
But that "one guy" happens to be an expert in the field. And his argument sounds fully baked to me.
But that is manifestly untrue. If every experiment confirmed Einstein we would not even be talking about dark matter.
> one guy with a half-baked argument
But that "one guy" happens to be an expert in the field. And his argument sounds fully baked to me.
Dark matter doesn't contradict general relativity, so it's entirely plausible that a) every experiment confirms Einstein, and yet b) we still need dark matter to explain some observations.
"Dark matter" is a synonym for "some unknown stuff that causes experiment to disagree with theory based on what we currently observe." It's not dark matter per se that contradicts GR, it is the experimental observations that require dark matter to be postulated in the first place that contradict GR.
No, there's nothing in the dark matter hypothesis or observations that necessarily contradicts GR.
However, it's true that some other theories that claim to explain the dark matter observations are in conflict with GR, which is why those theories are received very skeptically.
However, it's true that some other theories that claim to explain the dark matter observations are in conflict with GR, which is why those theories are received very skeptically.
> there's nothing in the dark matter hypothesis or observations that necessarily contradicts GR
That is true for the "hypothesis" part, it is not true for the "observations" part. The observations do contradict GR. To be precise, they are at odds with the predictions of GR on the assumption that the universe is made entirely of ordinary matter. So there are two possibilities: 1) GR is wrong, 2) the universe is not made entirely of ordinary matter, i.e. there is "something else", which we call "dark matter". The problem is, there is no evidence for the existence of dark matter other than the observations that are at odds with the predictions of GR, and so the possibility that GR could be wrong still needs to be taken seriously at this point.
That is true for the "hypothesis" part, it is not true for the "observations" part. The observations do contradict GR. To be precise, they are at odds with the predictions of GR on the assumption that the universe is made entirely of ordinary matter. So there are two possibilities: 1) GR is wrong, 2) the universe is not made entirely of ordinary matter, i.e. there is "something else", which we call "dark matter". The problem is, there is no evidence for the existence of dark matter other than the observations that are at odds with the predictions of GR, and so the possibility that GR could be wrong still needs to be taken seriously at this point.
“The observations do contradict GR” and “the observations are at odds with GR under the assumption that the universe is made of ordinary matter” are two very different statements, and the latter does not imply the former.
You could also say that deviations in Uranus’s orbit contradict GR under the assumption that Neptune doesn’t exist. But Neptune does exist, so this isn’t really a statement about GR at all.
You could also say that deviations in Uranus’s orbit contradict GR under the assumption that Neptune doesn’t exist. But Neptune does exist, so this isn’t really a statement about GR at all.
The difference is that Neptune is there, indeed, was discovered because it was exactly where Newtonian mechanics predicted it would be. The situation here is completely different because all of the plausible hypotheses about the nature of dark matter have been tested and falsified. The only thing left is "some weird stuff that is fundamentally unlike anything we have ever observed before". It is more analogous to the luminiferous aether than to Neptune. If that doesn't count as contradicting GR, at least potentially, then nothing contradicts anything because you can always resort to this kind of special pleading to explain any observation under any hypothesis.
Are you suggesting that all of the plausible hypotheses about the nature of dark matter have been tested and falsified?
I'm not suggesting it, those were literally the exact words that I wrote.
Of course, that claim turns entirely on the meaning of "plausible", so I'll amend my claim to simply say that all attempts to detect dark matter to date have failed.
Of course, that claim turns entirely on the meaning of "plausible", so I'll amend my claim to simply say that all attempts to detect dark matter to date have failed.
I’m no expert in this area, but my understanding is that weakly-interacting particles aren’t “something we’ve never seen before”, and in fact the neutrino is an excellent example of such a particle. However the neutrino isn’t a candidate for the specific particle causing the observed effect because the distribution of observed effects on normal matter would look different, hence the search for more massive particles: a search that is very much at its early stages.
> weakly-interacting particles aren’t “something we’ve never seen before”, and in fact the neutrino is an excellent example of such a particle.
That's right. But the only reason we know about the neutrino is that it was predicted by theory.
> However the neutrino isn’t a candidate for the specific particle causing the observed effect because the distribution of observed effects on normal matter would look different, hence the search for more massive particles:
Correct again.
> a search that is very much at its early stages.
That depends on what you consider "early". There are only so many places in the standard model that wimps can be hiding, and the vast majority of them (if not all of them -- I haven't been keeping up with the latest developments) have been ruled out.
https://www.nature.com/articles/d41586-020-02741-3
That's right. But the only reason we know about the neutrino is that it was predicted by theory.
> However the neutrino isn’t a candidate for the specific particle causing the observed effect because the distribution of observed effects on normal matter would look different, hence the search for more massive particles:
Correct again.
> a search that is very much at its early stages.
That depends on what you consider "early". There are only so many places in the standard model that wimps can be hiding, and the vast majority of them (if not all of them -- I haven't been keeping up with the latest developments) have been ruled out.
https://www.nature.com/articles/d41586-020-02741-3
Which is odd, because by far our best experimentally verified theory is also in conflict with GR. Our measurements for QED are orders of magnitude more accurate, so I'm inclined to believe GR is the incorrect theory.
Some of our measures of QED are very accurate (10 decimal places give or take), but the measurements QCD are much more complicated and the theory doesn't produce nearly as clean values. Also, there are purely QED experiments (muon G2 for example) where there are some serious contradictions.
Are you saying that GR has been contradicted by experimental observations?
I don't believe we have yet managed to conduct an experiment to detect dark matter. We have observations that seem to contradict Einstein, but no experiment that concludes. I believe a couple of experiments are currently underway, exciting times.
There are other hypotheses competing with dark matter which have revised models of gravity, it’s not just one guy:
https://en.wikipedia.org/wiki/Entropic_gravity
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
https://en.wikipedia.org/wiki/Entropic_gravity
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
The theory of gravitation is not at question here, it is in fact the basis for proposing the existing of some yet-unseen matter to account for why the observed galaxies behave. Someone proposing that there is no such thing as the thing we have never observed is... a pretty "baked" argument.
I would like to toss my own idea into this discussion. This idea incorporates a mechanism that would explain why gravity might slightly deviate from Newtonian and/or GR in some circumstances.
This paper also adapts GR in such a way that it is consistent with galactic rotation rates, the anisotropies of the CMB, and cosmological expansion -- while showing that the simple operation of gravity is the cause of each of these phenomena.
Cyclic Gravity and Cosmology (CGC) predicts that there are discrete specific sizes allowable for macro-objects. The instability of Bennu and the fact that it behaves more like loosely held scree rather than a compact mass -- is an example of a mass that is not exactly at one of the discrete allowable sizes. Please also refer to the link I included wherein I uploaded a video simulation of the formation of a solar system using this type of force law. (This is in section 18 of the paper)
I would greatly appreciate any comments on this idea. Copies may be downloaded here:
https://vixra.org/pdf/2203.0032v3.pdf
This paper also adapts GR in such a way that it is consistent with galactic rotation rates, the anisotropies of the CMB, and cosmological expansion -- while showing that the simple operation of gravity is the cause of each of these phenomena.
Cyclic Gravity and Cosmology (CGC) predicts that there are discrete specific sizes allowable for macro-objects. The instability of Bennu and the fact that it behaves more like loosely held scree rather than a compact mass -- is an example of a mass that is not exactly at one of the discrete allowable sizes. Please also refer to the link I included wherein I uploaded a video simulation of the formation of a solar system using this type of force law. (This is in section 18 of the paper)
I would greatly appreciate any comments on this idea. Copies may be downloaded here:
https://vixra.org/pdf/2203.0032v3.pdf
Actually, the hard thing about dark matter is that the arguments for it and the arguments against it are both relatively compelling. No matter how this shakes out, we're going to have a very different view of the universe when we finally understand what is really happening.
There aren't really any satisfactory alternatives to dark matter. The question is what exactly is it, and how did it get there.
> There aren't really any satisfactory alternatives to dark matter (given current models)
Dark Matter is a fudge factor used to account for quite good, but still incomplete physical modeling.
Dark Matter is a fudge factor used to account for quite good, but still incomplete physical modeling.
“Fudge factor” massively undersells it. For instance, measurements from the bullet cluster are quite compelling that there is significant mass in a galaxy that we don’t directly measure. That’s the definition of dark matter.
>the arguments for it
We don't understand why our numbers don't add up so we made up a number to explain it is "compelling" to you?
Dark matter has always reeked of "ether" to me. I looked into some of the alt science on this a long time ago. There is a compelling case that our model of gravity is wrong. Fortunately gravity is such a weak force that at small ie solar system scales it doesn't matter. Which is why we can launch satellites around the system. However the failure shows at large scale like galaxies.
We don't understand why our numbers don't add up so we made up a number to explain it is "compelling" to you?
Dark matter has always reeked of "ether" to me. I looked into some of the alt science on this a long time ago. There is a compelling case that our model of gravity is wrong. Fortunately gravity is such a weak force that at small ie solar system scales it doesn't matter. Which is why we can launch satellites around the system. However the failure shows at large scale like galaxies.
Dark matter isn't just a made-up number. It's an observed phenomenon that MOND and other modified-gravity theories cannot explain.
It is an observable fact that dark matter is a distinct substance from baryonic matter. Modified gravity is thoroughly disproven by the many galaxies that have been discovered that have been separated from their dark matter[1], or seem to have never had any in the first place [2]. A galaxy can't be separated from, or be lacking in, something that doesn't exist.
Any attempt to dismiss dark matter entirely without addressing this highly conclusive evidence is not valid.
1. https://www.wikiwand.com/en/Bullet_Cluster
2. https://www.inverse.com/science/dark-matter-in-galaxies
It is an observable fact that dark matter is a distinct substance from baryonic matter. Modified gravity is thoroughly disproven by the many galaxies that have been discovered that have been separated from their dark matter[1], or seem to have never had any in the first place [2]. A galaxy can't be separated from, or be lacking in, something that doesn't exist.
Any attempt to dismiss dark matter entirely without addressing this highly conclusive evidence is not valid.
1. https://www.wikiwand.com/en/Bullet_Cluster
2. https://www.inverse.com/science/dark-matter-in-galaxies
Its been a very long time since I looked at any of these stuff and I'm certainly not a subject matter expert. I just remember reading about it and the entire idea of dark matter and dark energy came from the fact that the math models they had at the time didn't add up. They needed a way to rectify the math and they did it by saying well if we put this LITERALLY made up number in the equations everything balances out. Then they made up the explanation as to why this number needed to exist as "dark matter/energy" There have been mountains of research made trying to prove this since then that muddy the water of how flimsy the origin was.
Dark matter has always smelled of phlogistons to me. It's this mystery substance that solves all of our problems, and doesn't make any predictions. I have no idea what a more accurate explanation for the observations would look like, but dark matter can't be it.
The thing is, it's an extremely simple mechanism which solves all our problems at once. Everything that's currently explained by that of one extra particle, would need separate explanations without dark matter; general relativity + dark matter fits all the data we have. It's not just about galaxy rotation speeds, it's about observations of gravitational mass (as measured by lensing) moving independently from the visible mass, it explains structure formation in the early universe, and other stuff.
It's such a simple explanation which explains so many otherwise unexplained things that I feel we should have pretty strong priors that it's true.
It does make the prediction that there's a lot of detectable massive particles out there. That's not a prediction which is easy to test, but to say there are no predictions isn't right.
It's such a simple explanation which explains so many otherwise unexplained things that I feel we should have pretty strong priors that it's true.
It does make the prediction that there's a lot of detectable massive particles out there. That's not a prediction which is easy to test, but to say there are no predictions isn't right.
My point is that the same could be said about phlogistons back in the day. There were a lot of completely different advances in the understanding of physics and chemistry needed to explain combustion and oxidation, and it's a lot more complex than just saying "because phlogistons". It was an extremely simple mechanism which solved all the problems at once, and fit all the data available at the time.
And it doesn't explain anything! We have this entirely new substance and we don't know what it is, what it's made of, where it came from, or why we only have circumstantial evidence for its presence.
And it doesn't explain anything! We have this entirely new substance and we don't know what it is, what it's made of, where it came from, or why we only have circumstantial evidence for its presence.
It does seem like that, and so there have been many attempts to revise the math to make it fit all known observations. But nobody has been successful, and so dark matter remains, at the very least, by far the best explanation we have. It fits the data.
> It fits the data.
To use an analogy from the world of finance, that sounds like building a Balance Sheet model that "plugs" Retained Earnings so that Assets and Liabilities always balance. Of course it fits the data, its very existence is to explain away the part of the model that doesn't fit the data
To use an analogy from the world of finance, that sounds like building a Balance Sheet model that "plugs" Retained Earnings so that Assets and Liabilities always balance. Of course it fits the data, its very existence is to explain away the part of the model that doesn't fit the data
Dark matter is not just an imaginary number that fills some holes in math. It is a thing that has been observed. Galaxies can have it or not have it. Galaxies can be separated from it in collisions. You can't be separated from something that doesn't exist.
This article has introduced me to "Modified Newtonian dynamics", which is a field of study I didn't know existed. The premise is pretty obvious now: Newton was pretty cool and all, but he wasn't right about high acceleration environments. Why then should we presume that he was be right about low acceleration environments, when the observations don't fit the predictions? The fact that nobody has come up with an answer doesn't mean there isn't any, and at least these people are actively trying to come up with one. I understand why the author appears to be very frustrated -- I'd be frothing-at-my-mouth angry in his position.
I wondered if this was a spin on this-(insert noun)-does-not-exist
Finland
That is dark man
Of course it does -- https://en.wikipedia.org/wiki/Dark_Matter_(TV_series)
Even better because the article link is on a .tv domain :)
Now all we need to find is its elusive 4th season...
Dark matter is all hand waves.
It’s not completely impossible that something doesn’t interact with the electromagnetic force… somewhere we’re missing something something.
Research seems to have calculated a bound on the large scale distribution of dark matter that shows it doesn't exist in extragalactic halos.
Article makes hyperbolic claims that "dark matter doesn't exist". This is junk, sorry. And that article makes me deeply distrust the otherwise-reasonable-seeming research.
Article makes hyperbolic claims that "dark matter doesn't exist". This is junk, sorry. And that article makes me deeply distrust the otherwise-reasonable-seeming research.
Hallelujah. Whenever scientists invent things we cannot measure to explain why their theories are still valid, you know you have a problem.
The three biggest issues with the sciences today are:
1) grant money purse strings controlled by bureaucrats with a political agenda
2) the "peer review process" and lack of open source, real-time, collaborative research
3) scientists who become dogmatic about their field of expertise, even if all of their work is built on a flawed theory
All three are interrelated and a cancer in terms of humanity's progress.
I'm sure you'll find plenty of examples of #3 in this thread, too.
The three biggest issues with the sciences today are:
1) grant money purse strings controlled by bureaucrats with a political agenda
2) the "peer review process" and lack of open source, real-time, collaborative research
3) scientists who become dogmatic about their field of expertise, even if all of their work is built on a flawed theory
All three are interrelated and a cancer in terms of humanity's progress.
I'm sure you'll find plenty of examples of #3 in this thread, too.
* DM particle haven't yet been found.
* The current best theory of the structure formation and galaxy evolution involves dark matter and critically depend on it to reproduce observations.
* There is a broad variety of Dark matter models that are consistent with simulations.
* It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.
* There are a few cases where you can find tensions with the existing DM based paradigm. I.e. the is test pointed in the article involving galactic bar in the paper "Fast galaxy bars continue to challenge standard cosmology". Note the toned down title. In this paper they just compared one specific feature of galactic disks in the simulations to the data and show that it doesn't match. I'd argue there are many reasons that could be the case that doesnt' involve killing DM. The same applies to other tensions.
* A final point. Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.