Physicists argue that black holes from the Big Bang could be the dark matter(quantamagazine.org)
quantamagazine.org
Physicists argue that black holes from the Big Bang could be the dark matter
https://www.quantamagazine.org/black-holes-from-the-big-bang-could-be-the-dark-matter-20200923/
109 comments
I’ve heard the same claim, and the reason given was that microlensing surveys would have found more of these black holes. The article gets into this near the end:
> For example, perhaps the strongest constraints on primordial black holes come from microlensing searches [...] In these efforts, astronomers monitor bright but distant sources, waiting to see if a dark object passes in front of them. These searches have long ruled out an evenly dispersed population of small black holes.
> But if primordial black holes exist at a range of masses, and if they’re packed into dense, massive clusters, those results could be less significant than researchers thought, García-Bellido said.
I heard about this most recently on Sean Carroll’s podcast:
https://www.preposterousuniverse.com/podcast/2020/05/11/96-l...
> For example, perhaps the strongest constraints on primordial black holes come from microlensing searches [...] In these efforts, astronomers monitor bright but distant sources, waiting to see if a dark object passes in front of them. These searches have long ruled out an evenly dispersed population of small black holes.
> But if primordial black holes exist at a range of masses, and if they’re packed into dense, massive clusters, those results could be less significant than researchers thought, García-Bellido said.
I heard about this most recently on Sean Carroll’s podcast:
https://www.preposterousuniverse.com/podcast/2020/05/11/96-l...
The lack of microlensing evidence is one reason. The other is that there are constraints on the amount of baryonic matter in the universe from nucleosynthesis calculations in the Big Bang (i.e. the extra missing matter needed to account for galactic rotation curves can't be 'ordinary' matter).
https://ned.ipac.caltech.edu/level5/March10/Garrett/Garrett3...
https://ned.ipac.caltech.edu/level5/March10/Garrett/Garrett3...
Primordial black hole would have formed before big bang nucleosynthesis and so would not contribute to the relevant amount of baryonic matter.
> Primordial black hole would have formed before big bang nucleosynthesis and so would not contribute to the relevant amount of baryonic matter.
What would they have been made up? Do quarks have mass, and there was enough of them? Or does energy through E=MC^2 mean that enough pure energy density can cause a black hole?
What would they have been made up? Do quarks have mass, and there was enough of them? Or does energy through E=MC^2 mean that enough pure energy density can cause a black hole?
> Or does energy through E=MC^2 mean that enough pure energy density can cause a black hole?
Yes! https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
Yes! https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
>What would they have been made up? Do quarks have mass, and there was enough of them? Or does energy through E=MC^2 mean that enough pure energy density can cause a black hole?
I'm not sure exactly when primordial blackholes would have formed but I think it would have been sometime after inflation, though perhaps before baryogenesis. Here's the reasoning: I think it would be after the GUT epoch so gravity would have splintered off from the other forces and I think it would have been after inflation started so that inflation had a chance to exaggerate the scale of quantum fluctuations to create the necessary size & scale of density fluctuations for blackholes to form.
Energy alone is enough to form a blackhole. However, it's not the energy density per se. That's sort of a necessary but not sufficient condition since you also need the surrounding spacetime to be at a low enough density relative to the region where you are expecting a blackhole to form.
This, incidentally is a common source of confusion about the big bang. "Why didn't it just form a blackhole?" The answer is because ALL of the spacetime was at the same density.
I'm not sure exactly when primordial blackholes would have formed but I think it would have been sometime after inflation, though perhaps before baryogenesis. Here's the reasoning: I think it would be after the GUT epoch so gravity would have splintered off from the other forces and I think it would have been after inflation started so that inflation had a chance to exaggerate the scale of quantum fluctuations to create the necessary size & scale of density fluctuations for blackholes to form.
Energy alone is enough to form a blackhole. However, it's not the energy density per se. That's sort of a necessary but not sufficient condition since you also need the surrounding spacetime to be at a low enough density relative to the region where you are expecting a blackhole to form.
This, incidentally is a common source of confusion about the big bang. "Why didn't it just form a blackhole?" The answer is because ALL of the spacetime was at the same density.
What does it mean for spacetime to have density?
I could say that a small sphere is denser than a large sphere because the distances between points are smaller on average, but that requires the spheres to be embedded in something with a distance metric(Euclidean 3-dimensional space).
What is the thing that spacetime is embedded in that provides a pointwise distance metric?
I could say that a small sphere is denser than a large sphere because the distances between points are smaller on average, but that requires the spheres to be embedded in something with a distance metric(Euclidean 3-dimensional space).
What is the thing that spacetime is embedded in that provides a pointwise distance metric?
This can be (kinda) explained via the notion of space-time expansion. (This is an intrinsic phenomenon, having nothing to do with objects moving through space.) As the space-time expands, its density becomes lower. The (relative) change in density can be measured indirectly by measuring (the effects of) the expansion.
A technical explanation of the expansion involves the inflaton field.
(There's also energy density of the gravitational field.)
A technical explanation of the expansion involves the inflaton field.
(There's also energy density of the gravitational field.)
This may help: Given a spacetime manifold with metric and no matter that is flat an infinity, you can mathematically define the amount of curvature in it, which is directly related to how much energy in conventional forms (say, kinetic) that could be transferred to matter. Just as two merging black holes can emit gravitational waves, which have energy in this sense and escape to infinity, gravitational waves coming in from infinity can collapse into a black hole where no black hole previously existed.
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Black holes are same as any other matter and the lensing is only dependent on mass. So if in a distant galaxy there is dark matter, the lensing will be exactly the same regardless fo whether this is in a form of cloud of particles or from billions of small black holes.
Microlensing surveys look for lensing of light from distant sources caused by relatively nearby masses.
The reasoning appears to be that if the BHs are clumped, then the number of microlensing events will be lowered, as opposed to if the BHs are evenly dispersed.
In other words, the number of concentrated masses intercepting rays of light from distant background sources would be given by the number of BH clusters as opposed to the number of BHs.
The objects we're looking for are large masses in the space between us and the distant light source. Typically the light source would be in the LMC or in our own galactic center, and the BHs would be, for example, in our own galactic halo.
We wouldn't expect to be finding BHs in a distant galaxy by microlensing.
I'm describing (or trying to describe!) what seems to be the astrophysics consensus. Sean Carroll is a Caltech astrophysicist who was interviewing another astrophysicist, and my quote from the article gives the explanation from a third. Am I getting this wrong?
In other words, the number of concentrated masses intercepting rays of light from distant background sources would be given by the number of BH clusters as opposed to the number of BHs.
The objects we're looking for are large masses in the space between us and the distant light source. Typically the light source would be in the LMC or in our own galactic center, and the BHs would be, for example, in our own galactic halo.
We wouldn't expect to be finding BHs in a distant galaxy by microlensing.
I'm describing (or trying to describe!) what seems to be the astrophysics consensus. Sean Carroll is a Caltech astrophysicist who was interviewing another astrophysicist, and my quote from the article gives the explanation from a third. Am I getting this wrong?
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What if antimatter, for some reason, clumped together more easily (weaker electric repulsion?). Wouldn't that cause more "anti-black holes" to form during the early period of the universe, explaining both matter/antimatter imbalance and part of the dark matter in the process?
And now I wonder the same as holler: firstly, can you differentiate a black hole made of matter from one made of antimatter? The resulting energy couldn't leave it, AFAIK?
Secondly, if there is any difference, what would happen to Earth in case of a collision?
And now I wonder the same as holler: firstly, can you differentiate a black hole made of matter from one made of antimatter? The resulting energy couldn't leave it, AFAIK?
Secondly, if there is any difference, what would happen to Earth in case of a collision?
I have also wondered about these kinds of large scale local asymmetries. I.e. "how do we know distant galaxies aren't made of antimatter?" There is a paper by prokhorov published in physical review D in 2015 which was able to set some limits based on signatures of proton-antiproton annihilation. They claim no such asymmetries over a 20 megaparsec distance scale.
> "how do we know distant galaxies aren't made of antimatter?"
I'm not an expert, but isn't that because we don't observe gamma rays from matter-antimatter annihilation in between the galaxies?
I'm not an expert, but isn't that because we don't observe gamma rays from matter-antimatter annihilation in between the galaxies?
> can you differentiate a black hole made of matter from one made of antimatter?
Not as far as I'm aware. A black hole is defined solely by its mass, charge and spin. What goes into it becomes irrelevant once it crosses the event horizon, except for those three factors.
(Though one does wonder, what happens if an object with negative mass enters a blackhole? But negative mass may not even exist.)
> Secondly, if there is any difference, what would happen to Earth in case of a collision?
None in practical terms.
Not as far as I'm aware. A black hole is defined solely by its mass, charge and spin. What goes into it becomes irrelevant once it crosses the event horizon, except for those three factors.
(Though one does wonder, what happens if an object with negative mass enters a blackhole? But negative mass may not even exist.)
> Secondly, if there is any difference, what would happen to Earth in case of a collision?
None in practical terms.
AFAIK (but I'm no physicist), a black hole has a quantum number of every single kind predicted by the Standard Model. So they'll have a baryonic number that can be zero or negative just as well as positive.
I'm interested in antimatter too. There should be a lot of antimatter out there, but we can't seem to find it. It's possible that antimatter does interact gravitationally at a smaller magnitude with matter and/or other antimatter. As far as I know, we haven't even experimentally confirmed whether antimatter has the same sign for gravitational effects as regular matter (ie whether it's repulsive or attractive), but it seems very likely that it's the same as regular matter. The magnitude could be different though.
Keep an eye on ALPHA at CERN. It is designed to answer this exact question by producing anti-hydrogen atoms. https://home.cern/news/news/physics/alpha-collaboration-cern.... Their initial results a few years back were consistent with matter and antimatter acting the same under gravity, but their error bars were large enough to warrant a more precise measurement, which they're up to now.
Thank you. I had read about their previous experiment but didn't know about what was going on now.
Would an antimatter black hole shrink when absorbing regular matter, or is the mass of the photons from the annihilation process the same as the mass of the annihilated particles? How would that work? Would annihilation even happen under such extreme conditions?
Adding antimatter to a matter black hole (don't think it matters actually, but this seems to be the case in question) should increase the mass and size, not decrease.
Correct, the photons produced from annihilation should match the inputs.
To decrease you'd need to add negative mass or negative energy, which aren't things we've found to exist yet.
We don't actually know _what_ will happen in the singularity of a black hole, to answer the question of if annihilation will happen there. As far as I know we don't have any model of what happens in a singularity.
Correct, the photons produced from annihilation should match the inputs.
To decrease you'd need to add negative mass or negative energy, which aren't things we've found to exist yet.
We don't actually know _what_ will happen in the singularity of a black hole, to answer the question of if annihilation will happen there. As far as I know we don't have any model of what happens in a singularity.
Matter annihilation conserves the energy (and as consequence, the mass) of the particles that were destroyed.
When anti-matter enters a black hole it shrinks the mass of the black hole. This is how blackholes emit Hawking radiation.
You're confusing antimatter with virtual particle pairs.
I think being able to tell the difference would have to be answered by solving the information loss problem. Because otherwise, every property is either dependent on or constrained only by the mass. And yes, even if they were antimatter black holes eating matter, it wouldn't matter because all the energy from the resulting annihilation would just stay in the black hole and due to mass-energy equivalence nothing would be different to the outside observer.
Couldn't the accretion disk of a black hole give us a clue though? Likely not all of the material would've been beyond the event horizon. Some of it would've stayed outside of it in the accretion disk. It's likely that the antimatter that stayed out would at some point interact with the regular matter that falls towards the black hole, but even that might give us a clue based on how energetic the accretion disk is (how much it radiates for example).
But I'm just guessing here.
But I'm just guessing here.
Well, probably not if we consider primordial black holes? Those can be quite light, and may have "cleared their orbit" a long time ago.
But I thought dark matter candidates needed to not interact with EM radiation in the same way ordinary matter does. Black holes are perfectly capable of absorbing light, wouldn't this effect be seen?
Perhaps they are so point-like that they can have sufficient density averaged out to account for the observed gravitational effects but a small enough cross-section that they contribute negligibly to light absorption?
Perhaps they are so point-like that they can have sufficient density averaged out to account for the observed gravitational effects but a small enough cross-section that they contribute negligibly to light absorption?
Given their mass would be, as the article says, the size of a large asteroid, the event horizon would be quite small. Ceres has a mass of 10^21kg, for example. This website[0] to calculate Schwartzchild radius estimates the event horizon for a black hole of that mass would be roughly 1 micro-meter (1 millionth of a meter).
[0]https://www.omnicalculator.com/physics/schwarzschild-radius
[0]https://www.omnicalculator.com/physics/schwarzschild-radius
Black holes this small would evaporate relatively quickly.
I don't know physics very well, but I was under the impression that our current models said that the primordial black holes would have evaporated by now. Perhaps there was some explanation for this in the article that I missed?
Would that evaporation be independent of matter accretion? Wouldn't a black hole of any size be able to sustain itself depending on the availability of matter in its catchment radius?
Or would black holes of smaller size not be able to capture enough matter to sustain themselves?
Or would black holes of smaller size not be able to capture enough matter to sustain themselves?
I think this is what you are referring to:
https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e...
"Hawking estimated that any black hole formed in the early universe with a mass of less than approximately 10^15 g would have evaporated completely by the present day."
https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e...
"Hawking estimated that any black hole formed in the early universe with a mass of less than approximately 10^15 g would have evaporated completely by the present day."
And the relevant part from the article discussing it:
> The original idea dates back to the 1970s with the work of Stephen Hawking and Bernard Carr. Hawking and Carr reasoned that in the universe’s first fractions of a second, small fluctuations in its density could have endowed lucky — or unlucky — regions with too much mass. Each of these regions would collapse into a black hole. The size of the black hole would be dictated by the region’s horizon — the parcel of space around any point reachable at the speed of light. Any matter within the horizon would feel the black hole’s gravity and fall in. Hawking’s rough calculations showed that if the black holes were bigger than small asteroids, they could plausibly still be lurking in the universe today.
This theory proposes the black holes would be big enough to still be around.
> The original idea dates back to the 1970s with the work of Stephen Hawking and Bernard Carr. Hawking and Carr reasoned that in the universe’s first fractions of a second, small fluctuations in its density could have endowed lucky — or unlucky — regions with too much mass. Each of these regions would collapse into a black hole. The size of the black hole would be dictated by the region’s horizon — the parcel of space around any point reachable at the speed of light. Any matter within the horizon would feel the black hole’s gravity and fall in. Hawking’s rough calculations showed that if the black holes were bigger than small asteroids, they could plausibly still be lurking in the universe today.
This theory proposes the black holes would be big enough to still be around.
I really appreciate how this theory makes testable predictions that already-planned experiments will be able to confirm or deny. Right or wrong (and most ideas are wrong), this is the gold standard of science.
If this were true, could the Earth ever collide with one of these asteroid-sized primordial black holes and what would happen? In theory would we even be able to detect the imminent rendezvous?
An asteroid-mass black hole would be too small to interact much. It would go straight through the planet, and couldn't possibly capture enough mass to be e.g. captured, but it would register as something like a very high energy cosmic ray.
I am interested in knowing your reasoning on how/why this will happen? (would go straight through the planet + would register as something like a very high energy cosmic ray)
I can answer the first question but not the second.
The Schwarzschild radius of Vesta is 396.1 nm [0]; which means it a black hole with that mass would intersect 6.281 cm^3 [1] of material if it went through the center of the Earth.
I have no idea why it might look like a cosmic ray. The surface gravity would be absolutely insane, so I would naïvely expect something like this look like an earthquake. [2]
[0] http://www.wolframalpha.com/input/?i=event%20Horizon%20radiu...
[1] http://www.wolframalpha.com/input/?i=%28396.1nm%29%5E2%20%2A...
[2] http://www.wolframalpha.com/input/?i=gravity%202.67%C3%9710%...
The Schwarzschild radius of Vesta is 396.1 nm [0]; which means it a black hole with that mass would intersect 6.281 cm^3 [1] of material if it went through the center of the Earth.
I have no idea why it might look like a cosmic ray. The surface gravity would be absolutely insane, so I would naïvely expect something like this look like an earthquake. [2]
[0] http://www.wolframalpha.com/input/?i=event%20Horizon%20radiu...
[1] http://www.wolframalpha.com/input/?i=%28396.1nm%29%5E2%20%2A...
[2] http://www.wolframalpha.com/input/?i=gravity%202.67%C3%9710%...
It wouldn't look like a cosmic ray to a physicist; that was a simplification.
It would leave a trail of wreckage behind it that, on a micro-scale, would look somewhat similar to that of a super-high-energy cosmic ray. A hole that large is large enough to swallow large numbers of atoms, and wrench the remaining ones out of position; that would look not too different from the damage you'd get if you sat in the way of a particle accelerator, at least very close to the path of the hole.
I'm not sure what would happen to you if one fell straight through you, but I suspect you'd be fine. (Unlike the particle accelerator, there wouldn't be much secondary radiation.)
Don't quote me on that, though. And don't try it at home, either.
It would leave a trail of wreckage behind it that, on a micro-scale, would look somewhat similar to that of a super-high-energy cosmic ray. A hole that large is large enough to swallow large numbers of atoms, and wrench the remaining ones out of position; that would look not too different from the damage you'd get if you sat in the way of a particle accelerator, at least very close to the path of the hole.
I'm not sure what would happen to you if one fell straight through you, but I suspect you'd be fine. (Unlike the particle accelerator, there wouldn't be much secondary radiation.)
Don't quote me on that, though. And don't try it at home, either.
>And don't try it at home, either.
If anyone out there does, in fact, manage to try this at home, please send a letter about it to the following address:
P.O. Box 5232, SE-102 45 Stockholm, Sweden
Street address: Sturegatan 14, Stockholm
If anyone out there does, in fact, manage to try this at home, please send a letter about it to the following address:
P.O. Box 5232, SE-102 45 Stockholm, Sweden
Street address: Sturegatan 14, Stockholm
There is a former Soviet Physicist who took a particle beam to the face.
https://en.m.wikipedia.org/wiki/Anatoli_Bugorski
https://en.m.wikipedia.org/wiki/Anatoli_Bugorski
wow! fascinating read...
"Bugorski understood the severity of what had happened, but continued working on the malfunctioning equipment, and initially opted not to tell anyone what had happened."
"The left half of Bugorski's face swelled up beyond recognition and, over the next several days, the skin started to peel, revealing the path that the proton beam (moving near the speed of light) had burned through parts of his face, his bone and the brain tissue underneath.[3] As it was believed that he had received far in excess of a fatal dose of radiation, Bugorski was taken to a clinic in Moscow where the doctors could observe his expected demise. However, Bugorski survived, completed his PhD, and continued working as a particle physicist.[4] There was virtually no damage to his intellectual capacity, but the fatigue of mental work increased markedly.[2] Bugorski completely lost hearing in the left ear, replaced by a form of tinnitus.[5] The left half of his face was paralyzed due to the destruction of nerves.[1] He was able to function well, excepting occasional complex partial seizures and rare tonic-clonic seizures."
"Bugorski understood the severity of what had happened, but continued working on the malfunctioning equipment, and initially opted not to tell anyone what had happened."
"The left half of Bugorski's face swelled up beyond recognition and, over the next several days, the skin started to peel, revealing the path that the proton beam (moving near the speed of light) had burned through parts of his face, his bone and the brain tissue underneath.[3] As it was believed that he had received far in excess of a fatal dose of radiation, Bugorski was taken to a clinic in Moscow where the doctors could observe his expected demise. However, Bugorski survived, completed his PhD, and continued working as a particle physicist.[4] There was virtually no damage to his intellectual capacity, but the fatigue of mental work increased markedly.[2] Bugorski completely lost hearing in the left ear, replaced by a form of tinnitus.[5] The left half of his face was paralyzed due to the destruction of nerves.[1] He was able to function well, excepting occasional complex partial seizures and rare tonic-clonic seizures."
I very much hope that, by the time someone can do this at home, the home in question is no closer than geostationary orbit.
Unlike a black hole falling in from deep space, one made on the surface of the Earth will definitely remain inside the planet, making one pass through the core every 42 minutes.
Unlike a black hole falling in from deep space, one made on the surface of the Earth will definitely remain inside the planet, making one pass through the core every 42 minutes.
In Dan Simmon's Hyperion, the Earth got gobbled up by a black hole in this way.
It's a good schema to get all the baggage of Earth out of the novel.
He just says, whoops, earth got eaten, don't worry about Yosemite anymore, now here are some space monks that live in huge bubbled space trees.
Much more fun than having to explain things minutely.
It's a good schema to get all the baggage of Earth out of the novel.
He just says, whoops, earth got eaten, don't worry about Yosemite anymore, now here are some space monks that live in huge bubbled space trees.
Much more fun than having to explain things minutely.
I suppose it has to do with the Schwarzschild radius of such a black hole being really small, I guess it would be something like 10^-8m according to https://en.wikipedia.org/wiki/Schwarzschild_radius which means almost nothing would fall inside its event horizon, and it probably would not collide with anything.
However, the gravitational pull of an asteroid would not be negligible, so I guess it would have a big impact pulling things towards it.
However, the gravitational pull of an asteroid would not be negligible, so I guess it would have a big impact pulling things towards it.
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Kurzgesagt has a video on small black holes. If memory serves, it's slightly worse than you suggest.
https://m.youtube.com/watch?v=8nHBGFKLHZQ
https://m.youtube.com/watch?v=8nHBGFKLHZQ
Nothing on this video is like the black holes people are discussing here.
First, they are big enough to be stable, they don't explosively evaporate in an instant. Second, they are much, much smaller than the large one on the video.
First, they are big enough to be stable, they don't explosively evaporate in an instant. Second, they are much, much smaller than the large one on the video.
The article was talking about asteroid sized (as in diameter), not mass.
https://www.wolframalpha.com/input/?i=black+hole+horizon+rad...
shows a black hole of mass 1×10^29 kg (which is about 1/20 of one solar mass) has a radius of 148.5 meters which is asteroid size.
https://www.wolframalpha.com/input/?i=gravity+of+1%C3%9710%5...
says at one earth's radius away that it has an escape velocity of 1447.5 km/s (kilometers per second), so yeah I think that will either destroy part of Earth or completely consume it, depending on how fast it's passing though.
For OP's question, whether it's detectable or not, it possibly is if it warps the light from background stars (same effect as https://en.wikipedia.org/wiki/Eddington_experiment).
https://www.wolframalpha.com/input/?i=black+hole+horizon+rad...
shows a black hole of mass 1×10^29 kg (which is about 1/20 of one solar mass) has a radius of 148.5 meters which is asteroid size.
https://www.wolframalpha.com/input/?i=gravity+of+1%C3%9710%5...
says at one earth's radius away that it has an escape velocity of 1447.5 km/s (kilometers per second), so yeah I think that will either destroy part of Earth or completely consume it, depending on how fast it's passing though.
For OP's question, whether it's detectable or not, it possibly is if it warps the light from background stars (same effect as https://en.wikipedia.org/wiki/Eddington_experiment).
Could this be related at all to Generic Objects of Dark Energy (GEODEs)?
https://en.wikipedia.org/wiki/Generic_object_of_dark_energy
https://en.wikipedia.org/wiki/Generic_object_of_dark_energy
It is shocking that 85% of matter is missing from our base model. Hope this solve it.
What if dark matter is just the clumping up of particles that don’t interact?
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Why would the clump if they don't interact?
Gravity still attracts them. They do have mass
But without interacting they have no means to shed the energy they gain when attracted to other matter, so they won't clump like normal matter.
They interact with normal matter and themselves via the force of gravity...
But gravity is (effectively) a conservative force.
For the most part a dark matter particle attracted to another particle will just convert all the kinetic energy it gained during the attraction back to potential energy as it whizzes past and away from the other particle.
Normal matter particles can radiate away photons when they hit each other, ie friction, leading to a non-conservative interaction. This allows them to shed their energy and clump in a way dark matter can't.
For the most part a dark matter particle attracted to another particle will just convert all the kinetic energy it gained during the attraction back to potential energy as it whizzes past and away from the other particle.
Normal matter particles can radiate away photons when they hit each other, ie friction, leading to a non-conservative interaction. This allows them to shed their energy and clump in a way dark matter can't.
This is why there is still a lot of atomic hydrogen in interstellar space. Thermodynamics suggests the atoms should bind together and form molecular hydrogen, but since a hydrogen molecule has no dipole moment, two hydrogen atoms alone in space cannot easily radiate away the energy released when they would bind. So they don't bind.
I used to think this as well. However, all orbiting mass can shed energy via gravity waves, and by interaction that fling some mass out at high kinetic velocity while other mass sinks deeper, which is a primary method of star formation afaik. Basically, radiating each other instead of photons.
There is also the possibility of dark matter only forces and fields that don't affect normal matter, but allow dark matter to self interact to some extent.
There is also the possibility of dark matter only forces and fields that don't affect normal matter, but allow dark matter to self interact to some extent.
No, gravity is different to all other forces.
First it's not really a force, then it's attracting and distant. We don't even have a proper theory for it yet.
Sure gravity is different from the other forces. That changes nothing about what I said, because we do have a proper theory for it: General Relativity. General Relativity matches a vast number observations with stunning precision.
Of course General Relativity is not the final answer, we know that. But that does not mean we know nothing about gravity, or that we somehow can't use our current theory to make predictions.
Dark matter as a concept assumes General Relativity is good enough, and takes it as-is. Without modifying gravity we need some other way to explain the discrepancies like galactic rotation curves, and so for dark matter we add in some new, so-far unseen, particles. We also know they have to interact very weakly with normal matter besides gravity, otherwise we'd would already have noticed them in existing observations and experiments. Based on this we can make predictions.
What would happen if we have some matter that only interacts gravitationally buzzing around?
Well as mentioned in my previous post such matter can't cool down and clump like normal matter, so instead it would be spread out in diffuse blobs around galaxies. And when we model galaxies with such dark matter halos we find that indeed, that might explain galaxy rotation curves. It also makes other predictions which also seem to match other observations. So overall dark matter looks like a pretty good candidate.
The alternative of course is to assume there aren't dark matter particles, but rather that GR has to be replaced or modified in some non-trivial way. There are many people working on that.
However they're so far struggling, because it turns out to be very difficult to change or replace GR without failing to match existing observations. So that seems to indicate that GR is a pretty darn good theory of gravity.
Of course General Relativity is not the final answer, we know that. But that does not mean we know nothing about gravity, or that we somehow can't use our current theory to make predictions.
Dark matter as a concept assumes General Relativity is good enough, and takes it as-is. Without modifying gravity we need some other way to explain the discrepancies like galactic rotation curves, and so for dark matter we add in some new, so-far unseen, particles. We also know they have to interact very weakly with normal matter besides gravity, otherwise we'd would already have noticed them in existing observations and experiments. Based on this we can make predictions.
What would happen if we have some matter that only interacts gravitationally buzzing around?
Well as mentioned in my previous post such matter can't cool down and clump like normal matter, so instead it would be spread out in diffuse blobs around galaxies. And when we model galaxies with such dark matter halos we find that indeed, that might explain galaxy rotation curves. It also makes other predictions which also seem to match other observations. So overall dark matter looks like a pretty good candidate.
The alternative of course is to assume there aren't dark matter particles, but rather that GR has to be replaced or modified in some non-trivial way. There are many people working on that.
However they're so far struggling, because it turns out to be very difficult to change or replace GR without failing to match existing observations. So that seems to indicate that GR is a pretty darn good theory of gravity.
I think that meant something like don't interact with our "ordinary matter" in a way that we know.
That's essentially the leading theory. They're called WIMPs.
Thanks for the search term, I'll look into it.
I would guess that Axions are currently the leading candidate.
As a general category of theories that's called "cold dark matter" — it needs to interact with something in order to clump up / cool off, but perhaps not in a way that's very visible to us. A wikipedia excursion will net you a handful of such theories and their pros and cons.
What if dark matter is actually a secondary effect (a-la-turbulence) of the flow of space that gravity causes? (I know the idea that space can flow is a fringe idea, but it seems thinking broadly/laterally in this area is not a terrible idea?)
That would be a modified theory of gravity.
I don't know about the idea of turbulence but modified gravity is serious science.
It is just not the preferred explanation right now. An important reason is that AFAIK, none of these theories are currently able to match the observations without the dark matter they intend to eliminate.
I don't know about the idea of turbulence but modified gravity is serious science.
It is just not the preferred explanation right now. An important reason is that AFAIK, none of these theories are currently able to match the observations without the dark matter they intend to eliminate.
I've had a theory for years now that it is the opposite: eg that gravity is a second tier effect at shorter distance of normal matter consolidating in order to seek breaking through black holes into dark matter. So some form of entanglement as two universe membranes collide (aka the big bang) means "real matter" in this universe was but is no longer dark matter (this would only work in a dual universe system instead of a multiverse system I posit) but due to all matter entering via a single membrane collision point it is all some form of entangled (quantum or otherwise), so in this theory black holes aren't the dark matter, but the gateway for normal matter to become dark matter, transitioning back to the other universe. In this theory, dark matter would then be concentrated in the areas of our universe with sparse amounts of normal matter, a theoretically testable hypothesis at some point in the future.
I'm no physicist, theory was developed while doing Einstein inspired imagination visualization/simulation of the big bang. I know it's probably so wrong in so many ways it's not worth a normal physicist to respond to, just thought I'd share.
If I were correct, which I'm probably not, it would mean there are no "primordial black holes" that existed since the moment of the big bang, but rather as time went on the black holes were created and increase in number (also being part of what causes this universe to expand)
I'm no physicist, theory was developed while doing Einstein inspired imagination visualization/simulation of the big bang. I know it's probably so wrong in so many ways it's not worth a normal physicist to respond to, just thought I'd share.
If I were correct, which I'm probably not, it would mean there are no "primordial black holes" that existed since the moment of the big bang, but rather as time went on the black holes were created and increase in number (also being part of what causes this universe to expand)
This is basically equivalent to any other crackpot theory. You can’t through together a bunch of impressive sounding words and expect to get anything out of it. The one prediction I noticed that you made that “ dark matter would then be concentrated in the areas of our universe with sparse amounts of normal matter“ has already been proven to not be true. Dark matter is concentrated in galaxies.
Yep, I get shit on anytime I mention it, despite the disclaimers. Whatever, it's just a fucking thought experiment.
It's not fair to write that you have a "theory", then suddenly convert it to a "thought experiment" when someone points out the the one testable prediction you propose is already disproven. This is equivalent, though obviously lower stakes, to making a racist comment then saying it's "just a joke" when it's received badly.
If you want things to be received as a thought experiment, call it that up front. You'll get people thinking and talking about it. But the response you received is in line with what the word "theory" means in the scientific community.
If you want things to be received as a thought experiment, call it that up front. You'll get people thinking and talking about it. But the response you received is in line with what the word "theory" means in the scientific community.
> I'm no physicist, theory was developed while doing Einstein inspired imagination visualization/simulation of the big bang. I know it's probably so wrong in so many ways it's not worth a normal physicist to respond to, just thought I'd share.
Not sure how much more clear it can be... If the single word "theory" misapplied can't be seen through by such intelligences well what else is there to say than I'm sorry and I'll never mention it again. I'll stick to the theories I'm good at.
Not sure how much more clear it can be... If the single word "theory" misapplied can't be seen through by such intelligences well what else is there to say than I'm sorry and I'll never mention it again. I'll stick to the theories I'm good at.
When you use word with mostly clear Technical definitions and meanings, you open yourself up to refutation. What you wrote is almost equivalent to saying 2+2=47374636628
> the idea is appealing because it doesn’t invoke new particles or new physics theories. It just repurposes old elements.
Hope was that, dark matter puzzle may bring new physics . Primordial black holes will be interesting to watch.
Hope was that, dark matter puzzle may bring new physics . Primordial black holes will be interesting to watch.
Does dark matter emit hawking radiation?
This is going back many years, but I seem to recall that one of the arguments against primordial black holes is that - assuming Hawking radiation is correct - we should see evidence of black holes evaporating if they are of the correct size, but that hasn't been seen.
https://www.nature.com/articles/248030a0
https://www.nature.com/articles/248030a0
If it did, it wouldn't be dark.
For all reasonable sizes of black holes, the flux due to Hawking radiation would be _so ridiculously low_ that it wouldn't change anything about our usage of the term "dark matter".
In fact most dark matter models do assume some form of extremely weak interactions with normal matter or dark matter decay, which is how we try to detect dark matter. The effective flux from such interactions is a lot larger than Hawking radiation would be.
In fact most dark matter models do assume some form of extremely weak interactions with normal matter or dark matter decay, which is how we try to detect dark matter. The effective flux from such interactions is a lot larger than Hawking radiation would be.
Blackhole is a planet with enough mass to bend light.
Little off topic: have you already found a way to exit the local group and access other galaxies? This should be our priority!
just fyi, "dark matter" is not a matter at all. it is just a label for the leftovers in the mathematical equations that we use today to calculate "space stuff". scientists have made this up so they can keep using the math, even if the numbers don't add up. it's the same thing when large corporations use "good will" for differences in assets and liabilities in their accounting.
This is a bad comment, to learn more read https://en.m.wikipedia.org/wiki/Galaxy_rotation_curve
I do not understand how something without any direct evidence whatsoever became lodged in the paradigm of science. Dark matter is not necessary to explain galactic rotation curves.[1] The original observation that spawned the idea of dark matter was of a galaxy's rotation in isolation. But galaxies are not gravitationally isolated. I am unsure about the other stuffed lumped in that dark matter is supposed to explain. But the problem of galactic rotation curves has been elegantly solved without the need for dark matter.
[1] https://www.youtube.com/watch?v=PL0ewiwqoTw
[1] https://www.youtube.com/watch?v=PL0ewiwqoTw
I kind of like the term "error matter". It emphasizes that we're talking about error terms in the equations, yet admits that much of that error would be resolved by the existence of matter.
"Dark" is descriptive, but it requires that there actually be relatively normal matter involved, which is going forward an unwarranted step. And then it gets reused for "dark energy", which is... what, energy you can't see or interacts weakly with existing sensors? That's not novel or even unusual. The phrase is bogus. "Error energy" would work.
"Dark" is descriptive, but it requires that there actually be relatively normal matter involved, which is going forward an unwarranted step. And then it gets reused for "dark energy", which is... what, energy you can't see or interacts weakly with existing sensors? That's not novel or even unusual. The phrase is bogus. "Error energy" would work.
That is being willfully ignorant.
Yes, "dark matter" is a kind of catch all term for a bunch of phenomenon / experimental measurements we don't properly understand. There's a large number of different models trying to describe the seen behavior and make predictions to be able to detect it. And in most of those models, dark matter is indeed matter!
Yes, "dark matter" is a kind of catch all term for a bunch of phenomenon / experimental measurements we don't properly understand. There's a large number of different models trying to describe the seen behavior and make predictions to be able to detect it. And in most of those models, dark matter is indeed matter!
This is a view which is increasingly disfavoured by scientists. Theories which attempt to modify the mathmatics to explain dark matter have failed to hold up to observation, and more and more evidence is mounting that dark matter does in fact act like matter.
> mounting that dark matter does in fact act like matter.
Apart from that the only way it interacts with anything else is via gravity...
Apart from that the only way it interacts with anything else is via gravity...
There's nothing inconsistent with a form of matter which only interacts through gravity (plenty of matter does not interact with e.g. electromagnetism), especially if you weaken the statement to a form of matter which we can only currently detect through the gravitation effects it seems to have.
Although it's always interesting to ask if there might be multiple kinds, which interact with each other in much the same way our own matter does.
Not all that likely, I know, but good for an SF story.
Not all that likely, I know, but good for an SF story.
My theory is that it IS gravity.
well, anything interacts with anything via gravity
What if the Big Bang Never Happened? https://www.youtube.com/watch?v=3KkhRibBllU
> Lerner received a BA in physics from Columbia University[7] and started as a graduate student in physics at the University of Maryland, but left after a year due to his dissatisfaction with the mathematical rather than experimental approach there.[8][9] He then pursued a career in popular science writing.
and
> He wrote the 1991 book The Big Bang Never Happened, which advocates Hannes Alfvén's plasma cosmology instead of the Big Bang theory. He is founder, president, and chief scientist of Lawrenceville Plasma Physics, Inc.
-- https://en.wikipedia.org/wiki/Eric_Lerner
he couldn't grok the Math and so he took to writing and scientific-populism.
and
> He wrote the 1991 book The Big Bang Never Happened, which advocates Hannes Alfvén's plasma cosmology instead of the Big Bang theory. He is founder, president, and chief scientist of Lawrenceville Plasma Physics, Inc.
-- https://en.wikipedia.org/wiki/Eric_Lerner
he couldn't grok the Math and so he took to writing and scientific-populism.
While he does seem like tbe crackpot-type, your last point may not be fair. I don’t think you can get through a undergrad physics education without being able to handle a decent amount of math. It sounds like it was just unfortunate he couldn’t find a experimental physics group as a grad student. I am surprised about this though, while I don’t know how it was back then, UM has an amazing experimental physics program now.
Of course this is way above my pay grade.