Emergent Gravity and the Dark Universe(arxiv.org)
arxiv.org
Emergent Gravity and the Dark Universe
https://arxiv.org/abs/1611.02269
84 comments
If you're wondering how this isn't some weird form of MOND, which is basically dead as an explanation, here's an important paragraph from the paper:
> We like to emphasize that we have not derived the theory of modified Newtonian dynamics as proposed by Milgrom. In our description there is no modification of the law of inertia, nor is our result (7.43) to be interpreted as a modified gravitational field equation. It is derived from an estimate of an effect induced by the displacement of the free energy of the underlying microscopic state of de Sitter space due to matter. This elastic response is then reformulated as an estimate of the gravitational self-energy due to the apparent dark matter in the form of the integral relation (7.40). Hence, although we derived the same relation as modified Newtonian dynamics, the physics is very different. For this reason we referred to the relation (7.43) as a fitting formula, since it is important to make a clear separation between an empirical relation and a proposed law of nature. There is little dispute about the observed scaling relation (7.43), but the disagreement in the scientific community has mainly been about whether it represents a new law of physics. In our description it does not.
> We like to emphasize that we have not derived the theory of modified Newtonian dynamics as proposed by Milgrom. In our description there is no modification of the law of inertia, nor is our result (7.43) to be interpreted as a modified gravitational field equation. It is derived from an estimate of an effect induced by the displacement of the free energy of the underlying microscopic state of de Sitter space due to matter. This elastic response is then reformulated as an estimate of the gravitational self-energy due to the apparent dark matter in the form of the integral relation (7.40). Hence, although we derived the same relation as modified Newtonian dynamics, the physics is very different. For this reason we referred to the relation (7.43) as a fitting formula, since it is important to make a clear separation between an empirical relation and a proposed law of nature. There is little dispute about the observed scaling relation (7.43), but the disagreement in the scientific community has mainly been about whether it represents a new law of physics. In our description it does not.
There seems to be considerable disagreement in the field. Why is it news (I really would like to know!)?
+ Kobakhidze explaining neutron experiments: https://arxiv.org/abs/1108.4161
+ http://physics.stackexchange.com/questions/4289/is-gravity-a...
+ Lubos Motl: http://motls.blogspot.nl/2010/01/erik-verlinde-why-gravity-c... and http://motls.blogspot.nl/2010/01/erik-verlinde-comments-abou...
It's nice to see that also experts in these highly specified fields quarrel about what it means to be "entropic" and "irreversible", etc.
+ Kobakhidze explaining neutron experiments: https://arxiv.org/abs/1108.4161
+ http://physics.stackexchange.com/questions/4289/is-gravity-a...
+ Lubos Motl: http://motls.blogspot.nl/2010/01/erik-verlinde-why-gravity-c... and http://motls.blogspot.nl/2010/01/erik-verlinde-comments-abou...
It's nice to see that also experts in these highly specified fields quarrel about what it means to be "entropic" and "irreversible", etc.
I think it helps a lot to try to understand the universe from an engineering perspective, thus by posing the question "How would I build a universe?"
The apparent obvious answer is : as an N dimensional matrix where each cell executes some code.
With such a setup, effects like gravity, are more probable to be emergent effects.
Another consideration is that in such a setup the only thing that matters is the state of the matrix, in other words there is no time, just iterations.
So my 2 cents are: gravity should be explained as an emergent phenomenon, and time should be removed from all equations that try to explain the underlying fabric of reality.
With such a setup, effects like gravity, are more probable to be emergent effects.
Another consideration is that in such a setup the only thing that matters is the state of the matrix, in other words there is no time, just iterations.
So my 2 cents are: gravity should be explained as an emergent phenomenon, and time should be removed from all equations that try to explain the underlying fabric of reality.
> According to the holographic principle, all the information in the entire universe can be described on a giant imaginary sphere around it. Verlinde now shows that this idea is not quite correct: part of the information in our universe is contained in space itself.
I thought the holographic principle just said the amount of information in any physical structure (up to the whole universe) was such that it could fit on a 2D surface the size of the event horizon of the structure, not that it actually is contained on the surface. Does this theory change that?
I thought the holographic principle just said the amount of information in any physical structure (up to the whole universe) was such that it could fit on a 2D surface the size of the event horizon of the structure, not that it actually is contained on the surface. Does this theory change that?
Imagining gravitational waves inevitably leads me to believe that gravity is a force that varies (in a cycle) over spacetime. But.. what exactly does it mean to propagate over a cycle in spacetime? (particularly the time aspect confuses me since something propagating in space remains constant in time (either accelerating or decelerating)
[deleted]
An explanation by the author: https://www.youtube.com/watch?v=ynRVnIh6wq4
Also, a simple explanation for the layman:
http://www.alphagalileo.org/ViewItem.aspx?ItemId=169788&Cult...
Thanks for the link (+1) but it's very far from being an explanation for the layman.
> In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime.
It doesn't explain how gravity emerges from bits of information. I'd love to understand how those bits make apples move from trees to the ground, the equivalence between gravity and acceleration and the weightless free fall experience. That should be one paragraph for the general principle and one for each example. Then it's for the layman, and me too :-)
> In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime.
It doesn't explain how gravity emerges from bits of information. I'd love to understand how those bits make apples move from trees to the ground, the equivalence between gravity and acceleration and the weightless free fall experience. That should be one paragraph for the general principle and one for each example. Then it's for the layman, and me too :-)
i think at the scale of a tree and an apple such insight would be a clear revolution stead essentially a whitepaper
but from the perspective of the paper i think this answers your initial question:
> It doesn't explain how gravity emerges from bits of information.
resides on large scales, infored bu flattening of rotational curves, and entanglement entropy(o)
there is a known relation, inequality, between entanglement entropy, a subsequent of quantum information, and large scale gravitational considerations
should one interpret the relation as 'emergent' or 'coincidence' it would seem a viable avenue of investigation
from the paper:
> 1.3 Hints from observations: the missing mass problem
> ...The observed flattening of rotation curves, as well as many other observations of dark matter phenomena, indicate that they are controlled by the Hubble acceleration scale a0, as first pointed out by Milgrom...
> ...Consider a spherical region with boundary area A(r) = 4πr2 that contains matter with total mass M near its center...
> ...The appearance of the cosmological acceleration scale a0 in galactic dynamics is striking and gives a strong hint towards an explanation in terms of emergent gravity, as envisaged in [38].
> To make this point more clear let us rewrite the above inequality as SM = 2πM/ha0 < A(r)/4Gh (1.4)
> The quantity on the left hand side represents the change in the de Sitter entropy caused by adding the mass M, while the right hand side is the entropy of a black hole that would fit inside the region bounded by the area A.
> Our goal is to give a theoretical explanation for why the emergent laws of gravity differ from those of general relativity precisely when the inequality (1.4) is obeyed.
> We will find that this criterion is directly related to the presence of the volume law contribution to the entanglement entropy.
> At scales much smaller than the Hubble radius gravity is in most situations well described by general relativity, because the entanglement entropy is still dominated by the area law of the vacuum.
that last quote seems to reference the apple
(o) https://en.wikipedia.org/wiki/Entropy_of_entanglement
but from the perspective of the paper i think this answers your initial question:
> It doesn't explain how gravity emerges from bits of information.
resides on large scales, infored bu flattening of rotational curves, and entanglement entropy(o)
there is a known relation, inequality, between entanglement entropy, a subsequent of quantum information, and large scale gravitational considerations
should one interpret the relation as 'emergent' or 'coincidence' it would seem a viable avenue of investigation
from the paper:
> 1.3 Hints from observations: the missing mass problem
> ...The observed flattening of rotation curves, as well as many other observations of dark matter phenomena, indicate that they are controlled by the Hubble acceleration scale a0, as first pointed out by Milgrom...
> ...Consider a spherical region with boundary area A(r) = 4πr2 that contains matter with total mass M near its center...
> ...The appearance of the cosmological acceleration scale a0 in galactic dynamics is striking and gives a strong hint towards an explanation in terms of emergent gravity, as envisaged in [38].
> To make this point more clear let us rewrite the above inequality as SM = 2πM/ha0 < A(r)/4Gh (1.4)
> The quantity on the left hand side represents the change in the de Sitter entropy caused by adding the mass M, while the right hand side is the entropy of a black hole that would fit inside the region bounded by the area A.
> Our goal is to give a theoretical explanation for why the emergent laws of gravity differ from those of general relativity precisely when the inequality (1.4) is obeyed.
> We will find that this criterion is directly related to the presence of the volume law contribution to the entanglement entropy.
> At scales much smaller than the Hubble radius gravity is in most situations well described by general relativity, because the entanglement entropy is still dominated by the area law of the vacuum.
that last quote seems to reference the apple
(o) https://en.wikipedia.org/wiki/Entropy_of_entanglement
It's funny how scientists always reference time in relation to gravity and yet separate out gravity from other forces of motion when the implicate order would be to have gravity always playing a role in motion whatever the axis or motion of travel.
The other thing to know is that for a wave, there are more motions of travel than upon a triune 3-dimensional axis. The common thought process of a pondering individual is to simply add singular 3-dimensional particles to a 4, 5 or more dimensional time-space environment and try to peer into the behaviors of a hyperspatial-capable environment.
This is ridiculous because in a hyperspatial environment, so-called objects have a tendency to be in more of a wave-like state and even more-so than the waves of an ocean. These waves would be more like a fine-cotton tuft which is being pulled by electrostatic strands in multiple directions at once and wherein the "identities" of each may out of behavior dynamics be considered as singular with multiple locations because of a tendency to collapse at the same time or leave one the strongest through a matrix interconnections consisting of concepts of "Tensegrity." <wiki it.
Then you have photons which are thought to be low-mass or perhaps even zero or negative in mass. This seems to correlate nicely with their high-speed velocities.
In a Universe which has hyper-spatial dimensions not only overlaying reality but also underpinning it via multiple directions (like the gravity of multiple stars, planets, and moons affecting each planetary body), the hyper-spatial arenas would seem to be more elastic and able to slip and slide over and around the greater reality. Mystics and even scientists talk about these other dimensions as a deeper reality but it might be fair to take it with a grain of salt and see our current average reality as the "deeper reality."
So gravity is the "sums" of multiple affecting bodies. The datastreams coming in from the Sun, Moon, and other planets all affect life on Earth. The Moon mostly contributes to water while other elements likely have greater response to other planetary bodies, depending on their molecular and nuclear composition. (although this has not been published in the traditional manuscripts of current science)
Anyway, to answer the question in the way I think of it, gravity is related more closely to time than the way in which science usually connects time to gravity. Scientists usually act like a photon travels at the 299 792 458 m / s rate.
It would seem that whatever forces of information flow (entropy...and some would say proto-consciousness) are behind gravity - are also interrelated with time itself.
Here's the kicker. People assume everything falls to Earth. Why? Because most things do? What about balloons filled with Helium? What about light which reflects to the astronauts in space? What about the electrical currents flowing to the Sun and back in the chains of ions? How much mass is held in those ions?
And that's just talking "vertically" without reference towards the hyper-spatial dimensions which the common man has even less experience with - even though we are experiencing the interactions with these dimensions all the time.
Let me make an important note before I forget: Electromagnetic forces may very well be different enough from "gravity forces" to be differentiated but there may also certainly be some overlap at various scales or in high-voltage or highly-sophisticated quantum situations.
Whichever ways in which time is generated/observed/transmitted, both gravity and electromagnetic forces are bound to be related with the flow & effects. If information is practically as important as energy and gravity, how much information leaves Earth through light or ionic currents which flow to the Sun (or other stars?)
Also, to the person who also answered here and said electromagnetism can never be related with gravity, how do they imagine ions are moving through a wire or exchanged in an electrolyte solution of a battery or a hydrogen-production system? Again, to change the angle to "vertical" rather than horizontal is a weird way to classify an entirely different force.
Oh...as I was saying, :) it's all about the timing. In a coherent stream of information like a flow of photonic light or the flow of electrons in an electromagnetic current, the forces of motion are resistant to changes in the flow of time within their area of influence. Next move your attention to the heat we can "see" radiating from the smokestack of a semi tractor. This thermal emission is a form of energy which is slightly more disordered and "dispersed" than the kinds of "motion" we "see" elsewhere.
One would possible assume that if we get so close to Earth where we are essentially at "ground-level" and we allow the gravity well to exert its influence on an object, that the strong effect we see is because there is a very "unified" pull of forces. But this is just as false as if we get closer to a cable being weaved from dozens of smaller diameter threads. We begin 'seeing' the smaller threads are spread further apart as we change our perspective to a smaller and closer entity.
Why do we see water swirling different rotations into a drain on different places upon Earth? All to due with the nature of time, gravity, and space itself being shaped and molded by a force which is positional and situational and thus inherently "proto-conscious."
Link: Implicate Order: http://www.bizint.com/stoa_del_sol/plenum/plenum_3.html
The other thing to know is that for a wave, there are more motions of travel than upon a triune 3-dimensional axis. The common thought process of a pondering individual is to simply add singular 3-dimensional particles to a 4, 5 or more dimensional time-space environment and try to peer into the behaviors of a hyperspatial-capable environment.
This is ridiculous because in a hyperspatial environment, so-called objects have a tendency to be in more of a wave-like state and even more-so than the waves of an ocean. These waves would be more like a fine-cotton tuft which is being pulled by electrostatic strands in multiple directions at once and wherein the "identities" of each may out of behavior dynamics be considered as singular with multiple locations because of a tendency to collapse at the same time or leave one the strongest through a matrix interconnections consisting of concepts of "Tensegrity." <wiki it.
Then you have photons which are thought to be low-mass or perhaps even zero or negative in mass. This seems to correlate nicely with their high-speed velocities.
In a Universe which has hyper-spatial dimensions not only overlaying reality but also underpinning it via multiple directions (like the gravity of multiple stars, planets, and moons affecting each planetary body), the hyper-spatial arenas would seem to be more elastic and able to slip and slide over and around the greater reality. Mystics and even scientists talk about these other dimensions as a deeper reality but it might be fair to take it with a grain of salt and see our current average reality as the "deeper reality."
So gravity is the "sums" of multiple affecting bodies. The datastreams coming in from the Sun, Moon, and other planets all affect life on Earth. The Moon mostly contributes to water while other elements likely have greater response to other planetary bodies, depending on their molecular and nuclear composition. (although this has not been published in the traditional manuscripts of current science)
Anyway, to answer the question in the way I think of it, gravity is related more closely to time than the way in which science usually connects time to gravity. Scientists usually act like a photon travels at the 299 792 458 m / s rate.
It would seem that whatever forces of information flow (entropy...and some would say proto-consciousness) are behind gravity - are also interrelated with time itself.
Here's the kicker. People assume everything falls to Earth. Why? Because most things do? What about balloons filled with Helium? What about light which reflects to the astronauts in space? What about the electrical currents flowing to the Sun and back in the chains of ions? How much mass is held in those ions?
And that's just talking "vertically" without reference towards the hyper-spatial dimensions which the common man has even less experience with - even though we are experiencing the interactions with these dimensions all the time.
Let me make an important note before I forget: Electromagnetic forces may very well be different enough from "gravity forces" to be differentiated but there may also certainly be some overlap at various scales or in high-voltage or highly-sophisticated quantum situations.
Whichever ways in which time is generated/observed/transmitted, both gravity and electromagnetic forces are bound to be related with the flow & effects. If information is practically as important as energy and gravity, how much information leaves Earth through light or ionic currents which flow to the Sun (or other stars?)
Also, to the person who also answered here and said electromagnetism can never be related with gravity, how do they imagine ions are moving through a wire or exchanged in an electrolyte solution of a battery or a hydrogen-production system? Again, to change the angle to "vertical" rather than horizontal is a weird way to classify an entirely different force.
Oh...as I was saying, :) it's all about the timing. In a coherent stream of information like a flow of photonic light or the flow of electrons in an electromagnetic current, the forces of motion are resistant to changes in the flow of time within their area of influence. Next move your attention to the heat we can "see" radiating from the smokestack of a semi tractor. This thermal emission is a form of energy which is slightly more disordered and "dispersed" than the kinds of "motion" we "see" elsewhere.
One would possible assume that if we get so close to Earth where we are essentially at "ground-level" and we allow the gravity well to exert its influence on an object, that the strong effect we see is because there is a very "unified" pull of forces. But this is just as false as if we get closer to a cable being weaved from dozens of smaller diameter threads. We begin 'seeing' the smaller threads are spread further apart as we change our perspective to a smaller and closer entity.
Why do we see water swirling different rotations into a drain on different places upon Earth? All to due with the nature of time, gravity, and space itself being shaped and molded by a force which is positional and situational and thus inherently "proto-conscious."
Link: Implicate Order: http://www.bizint.com/stoa_del_sol/plenum/plenum_3.html
I don't have time to go over all your post, but you seem to be very very confused about several things. I suggest you try to read a science communication book, like Carl Sagan or the sort.
Gravity might have a lot to do with the electro-magnetism force. I've written "electro" separately on purpose because gravity and electromagnetic force might fundamentally be the same forces caused by the same electrons. Remember both magnetic and gravity forces act vertically. The gravity might be just an EM force on the pull mode.
Not even remotely the case, although I'd be fascinated to see where you got this notion from.
I mean, one could argue that perhaps EM is really a special kind of gravitational ripple (eg, geons might work out in quantum gravity to model electrons and photons, and then the question arises that if all EM is gravity induced and modeled, is EM not part of gravity?), but I don't know that I've heard it the other way.
It's also certainly not the mainstream view, as classical geons are extremely unstable.
It's also certainly not the mainstream view, as classical geons are extremely unstable.
I'm not sure how EM and Gravity could be unified as a single force, especially since the best theory of gravity that's out there describes gravity as curvature in spacetime, not a force.
If this is true, the literature I've read--as a layman myself reading from sources written for the layman on the subject--is wildly misleading.
i.e. from the Wikipedia article: https://en.wikipedia.org/wiki/Fundamental_interaction
>Other theorists seek to quantize the gravitational field by the modelling behaviour of its hypothetical force carrier, the graviton and achieve quantum gravity (QG).
i.e. from the Wikipedia article: https://en.wikipedia.org/wiki/Fundamental_interaction
>Other theorists seek to quantize the gravitational field by the modelling behaviour of its hypothetical force carrier, the graviton and achieve quantum gravity (QG).
Thanks for the layman link... I started reading and encountered a concept I didn't understand so I googled it. Then, I encountered another concept I didn't understand and google that, again and again, until I was several pages deep and only on the second sentence of the paper's description. TIL I don't know as much as I thought.
Wow, contrast on that text... Fail.
Gravitons always struck me as a goofy half-baked concoction (even though we've supposedly observed them now), and so did dark matter. Emergent gravity theories are very interesting.
Gravitons appear in several different families of theory.
We have not observed any of them; the interaction cross-section is so small (because gravity is so weak) that we have no hope of observing a single graviton, or failing to observe an expected one, any time soon.
Gravitational waves have spin 2 symmetry and are massless. A straightforward quantization of a gravitational wave leads to gravitons as a spin 2 massless gauge boson. Conversely, in almost any gauge theory that admits a massless spin 2 particle, that particle mediates a force almost exactly like gravitation, and is amenable to analysis under the Paramaterized Post-Newtonian Formalism.
Indeed, when gravity is weak, such theories essentially exactly reproduce General Relativity. It's only in strong gravity that non-negligible differences appear, and in this case strong gravity is when the quantum uncertainty in curvature distorts distances in ways that can't be worked around e.g by a change of basis or system of coordinates. Alternatively, gravity is strong when you have multiple loops of gravitons in a Feynman diagram.
So in the type of quantization above, the problem is that the momentum carried by an individual graviton is much much much much smaller than that carried by an individual low frequency photon. For example, a near-infrared photon has a momentum-energy on the order of about 1 eV/c^2, a 100 MHz photon has an energy on the order of 10^-7 eV/c^2, and a graviton will be less than 10^-22 eV/c^2 (LIGO collab., https://arxiv.org/abs/1602.03837, about six paragraphs before section VIII).
In other words, even the extremely weak signals LIGO's detected represent waves comprising huuuuuuge numbers of gravitons. But each graviton is so weak (or equilvalent long-wavelengthed) that we have no hope of detecting it individually. Think of how much fun you would have trying to isolate with your fingers an individual molecule of water in a surfers-beware ocean wave -- that'd be easier than isolating a graviton from a presently-detectable GW.
We have not observed any of them; the interaction cross-section is so small (because gravity is so weak) that we have no hope of observing a single graviton, or failing to observe an expected one, any time soon.
Gravitational waves have spin 2 symmetry and are massless. A straightforward quantization of a gravitational wave leads to gravitons as a spin 2 massless gauge boson. Conversely, in almost any gauge theory that admits a massless spin 2 particle, that particle mediates a force almost exactly like gravitation, and is amenable to analysis under the Paramaterized Post-Newtonian Formalism.
Indeed, when gravity is weak, such theories essentially exactly reproduce General Relativity. It's only in strong gravity that non-negligible differences appear, and in this case strong gravity is when the quantum uncertainty in curvature distorts distances in ways that can't be worked around e.g by a change of basis or system of coordinates. Alternatively, gravity is strong when you have multiple loops of gravitons in a Feynman diagram.
So in the type of quantization above, the problem is that the momentum carried by an individual graviton is much much much much smaller than that carried by an individual low frequency photon. For example, a near-infrared photon has a momentum-energy on the order of about 1 eV/c^2, a 100 MHz photon has an energy on the order of 10^-7 eV/c^2, and a graviton will be less than 10^-22 eV/c^2 (LIGO collab., https://arxiv.org/abs/1602.03837, about six paragraphs before section VIII).
In other words, even the extremely weak signals LIGO's detected represent waves comprising huuuuuuge numbers of gravitons. But each graviton is so weak (or equilvalent long-wavelengthed) that we have no hope of detecting it individually. Think of how much fun you would have trying to isolate with your fingers an individual molecule of water in a surfers-beware ocean wave -- that'd be easier than isolating a graviton from a presently-detectable GW.
Gravitons are simply quanta of gravitational waves. They arise in the same way as photons in electromagnetism. There's nothing goofy about them.
> even though we've supposedly observed [gravitons] now
Source? Or are you saying that the existence of gravitational waves constitute a proof of the existence of gravitons, due to wave/particle duality?
I'm not a physicist, but all I thought we had detected were gravitational waves.
Source? Or are you saying that the existence of gravitational waves constitute a proof of the existence of gravitons, due to wave/particle duality?
I'm not a physicist, but all I thought we had detected were gravitational waves.
> the existence of gravitational waves constitute a proof of the existence of gravitons, due to wave/particle duality
I always thought this is the case. But IANAP either. Could anyone with actual knowledge chime in?
I always thought this is the case. But IANAP either. Could anyone with actual knowledge chime in?
No, a gravitational wave has mass (carries mass is more accurate), but a graviton does not. They are not two aspects of the same thing.
Gravitational wave doesn't carry mass. It travels at the speed of light, so it has to be massless. In fact, in 4D gravitational waves can arise even without any mass/energy source.
See here: https://en.wikipedia.org/wiki/Sticky_bead_argument
I suppose I should have said energy, not mass, but unlike a photon which can disappear into nothing, leaving just the energy, a gravitational wave can't ever vanish entirely, so it's more like mass in that regard.
And don't forget that a wave can travel at the speed of light even if the wave is carried by massy particles that can not.
I suppose I should have said energy, not mass, but unlike a photon which can disappear into nothing, leaving just the energy, a gravitational wave can't ever vanish entirely, so it's more like mass in that regard.
And don't forget that a wave can travel at the speed of light even if the wave is carried by massy particles that can not.
> I suppose I should have said energy, not mass, but unlike a photon which can disappear into nothing, leaving just the energy, a gravitational wave can't ever vanish entirely, so it's more like mass in that regard.
This sentence is wrong. I'm not sure what you mind with "photon which can disappear into nothing, leaving just the energy", but gravitons [1] can do the same thing.
A gravitational wave is made of a huge amount of gravitons, it's like the electromagnetic wave produced by radio transmitter. I´m not sure if with your classification the electromagnetic wave produced by radio transmitter "can't ever vanish entirely".
[1] If they exist. I'm almost almost sure gravitons exist. There is still not a good quantum gravity theory, but I strongly believe that we will discover it in the future an it will include gravitons.
This sentence is wrong. I'm not sure what you mind with "photon which can disappear into nothing, leaving just the energy", but gravitons [1] can do the same thing.
A gravitational wave is made of a huge amount of gravitons, it's like the electromagnetic wave produced by radio transmitter. I´m not sure if with your classification the electromagnetic wave produced by radio transmitter "can't ever vanish entirely".
[1] If they exist. I'm almost almost sure gravitons exist. There is still not a good quantum gravity theory, but I strongly believe that we will discover it in the future an it will include gravitons.
> can disappear into nothing, leaving just the energy", but gravitons [1] can do the same thing.
I'm not convinced they can vanish, unlikely photons there is nothing that can stop a graviton, they are able to travel through all matter.
So given they have unlimited range, how would one vanish?
> A gravitational wave is made of a huge amount of gravitons
That is not established at all!! Not to mention it's mathematically identical to saying gravity is made up of gravitons, and we certainly have not established gravitons exist even for plain gravity.
After all a gravity wave is just a modulation in gravitational force, not some new entity.
I'm not convinced they can vanish, unlikely photons there is nothing that can stop a graviton, they are able to travel through all matter.
So given they have unlimited range, how would one vanish?
> A gravitational wave is made of a huge amount of gravitons
That is not established at all!! Not to mention it's mathematically identical to saying gravity is made up of gravitons, and we certainly have not established gravitons exist even for plain gravity.
After all a gravity wave is just a modulation in gravitational force, not some new entity.
Gravitons (if they exist) will interact with any particle with mass, so a big heavy wall should stop them. Since the interaction is extremely small, the wall must be extremely heavy, probably bigger than a galaxy, not just a normal wall.
>> A gravitational wave is made of a huge amount of gravitons
> That is not established at all!!
Completely agree. My conviction that they exist is based in many assumptions. In particular that we will someday have a quantum gravity theory that will be correct and that it will integrate nicely with the other physics theories. It's a good guess, but it's possible that we will not know the answer for hundreds of years.
>> A gravitational wave is made of a huge amount of gravitons
> That is not established at all!!
Completely agree. My conviction that they exist is based in many assumptions. In particular that we will someday have a quantum gravity theory that will be correct and that it will integrate nicely with the other physics theories. It's a good guess, but it's possible that we will not know the answer for hundreds of years.
> Gravitons (if they exist) will interact with any particle with mass
Yes. Except gravity actually interacts with any particle with energy, not just mass.
> so a big heavy wall should stop them
No. There is no way (as far as we know) to shield against gravity. Unlike charge, we don't even know of any way to attenuate it, never mind shield.
Yes. Except gravity actually interacts with any particle with energy, not just mass.
> so a big heavy wall should stop them
No. There is no way (as far as we know) to shield against gravity. Unlike charge, we don't even know of any way to attenuate it, never mind shield.
Can you elaborate on what you mean by "a gravitational wave has mass (carries mass is more accurate)"? That doesn't fit my understanding of gravitational waves.
They can carry energy see: https://en.wikipedia.org/wiki/Sticky_bead_argument
In a quantum field theory, a wave implies a force carrying particle, does it not?
To be precise, particles (with precise momentum) are certain modes or excitations of a quantum field which is often governed by something like a wave equation. However, not all quantum fields (and their associated particles) are force carriers. These are usually just the gauge bosons.
In any case, though, noone has managed to quantize gravity yet (i.e. describe gravity as a quantum field theory with gravitons as force carriers), so we've detected just gravitational waves but no gravitons.
In any case, though, noone has managed to quantize gravity yet (i.e. describe gravity as a quantum field theory with gravitons as force carriers), so we've detected just gravitational waves but no gravitons.
Well, we've quantized gravitation extremely well - it's just perturbative quantum gravity, of which there are a couple flavours. In weak gravity it makes predictions identical to General Relativity, but is taken to be an effective field theory (in the Charles Wilson sense of "effective) in that we do not know how to deal with Feynman diagrams with more than a loop or two of gravitons, which only happens in strong gravity.
In these theories, gravitons are quantizations of the weak-field perturbations.
The non-renormalizability by power-set counting of gravity because it is a long-range force is a good result of perturbatively quantized gravity. Who knows if there is a workable way of renormalization by other methods? Not me.
Since we don't get strong gravity except close to a black hole singularity or in the extremely early universe, it's unfair and premature to say that the EFT approach has been unsuccessful.
In these theories, gravitons are quantizations of the weak-field perturbations.
The non-renormalizability by power-set counting of gravity because it is a long-range force is a good result of perturbatively quantized gravity. Who knows if there is a workable way of renormalization by other methods? Not me.
Since we don't get strong gravity except close to a black hole singularity or in the extremely early universe, it's unfair and premature to say that the EFT approach has been unsuccessful.
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Goofy in what way? All other known forces are carried by particles, so why not gravity?
Gravitons are basically unavoidable. They may not be fundamental particles, but they'll always show up in the long-wavelength approximation of any theory of quantum gravity that extends general relativity.
I love this, it feels cleaner and more elegant a solution than dark matter particles. However, nature doesn't care what we like, so that doesn't make it more likely to be true.
I agree that it sounds elegant, especially since it puts entropy/information into the core ontology so as to explain the arrow of time and thermodynamic behavior as part of the same theory that can account for Einsteinian space-time.
I just wish I understood enough physics to tell this paper from elegant-sounding word salad!
I just wish I understood enough physics to tell this paper from elegant-sounding word salad!
Dark matter is hilariously clean.
It's literally just
"Hey you know how there's like a bunch of particles that don't interact with EM forces?"
"Yeah"
"Well what if there's like a BUNCH of particles that don't interact with EM forces?"
"...oh hey that makes this math way easier"
It's literally just
"Hey you know how there's like a bunch of particles that don't interact with EM forces?"
"Yeah"
"Well what if there's like a BUNCH of particles that don't interact with EM forces?"
"...oh hey that makes this math way easier"
Like others have mentioned I'm not sure what happens now to the gravity waves we've detected.
I'm not convinced we have in fact detected gravity waves. From our point of view merging black holes would not move due to time dilation, but the waves detected are modeled after black holes without time dilation.
Although it's possible we detected a wave from a different source, not a black hole.
Although it's possible we detected a wave from a different source, not a black hole.
While we can never see them merging completely, we can see them asymptotically approach a merger, which does in fact take about 1/5th of a second to get most of the way there.
I'm currently reading The Confusion [0] and just got through Leibniz's explanation of monadology [1][2]. Summarized very very briefly, the idea is that every particle in the universe is a sort of computational device, and their actions/reactions are determined by their "perception" of all the other particles in the universe.
Does this research suggest that he may have been semi-correct??
[0] https://en.wikipedia.org/wiki/The_Confusion [1] https://en.wikipedia.org/wiki/Monadology [2] https://quantummoxie.wordpress.com/2014/09/09/neal-stephenso...
Does this research suggest that he may have been semi-correct??
[0] https://en.wikipedia.org/wiki/The_Confusion [1] https://en.wikipedia.org/wiki/Monadology [2] https://quantummoxie.wordpress.com/2014/09/09/neal-stephenso...
Frankly, I'd be surprised if anything ever suggested that Leibniz's colorful metaphysics was correct, even or incorrect.
Leibnizian monads are unextended and unable to act on one another (from §1 and §7 of the Monadology), which is to say that they're non-physical. On the other hand, as they're somehow supposed each to have a complete picture to the world (§56), they imply some form of non-locality. Which is to say that they're some very spooky things.
The thing that comes closest to Leibniz's monadology is the idea that the world is a simulation running inside a computer. But Leibniz's idea was more like that there is an arbitrarily large number of computers running the same simulation, while some of them also run artificial intelligences which just watch the simulation unfold.
Which is an idea I think can be fairly described as "completely nuts".
Leibnizian monads are unextended and unable to act on one another (from §1 and §7 of the Monadology), which is to say that they're non-physical. On the other hand, as they're somehow supposed each to have a complete picture to the world (§56), they imply some form of non-locality. Which is to say that they're some very spooky things.
The thing that comes closest to Leibniz's monadology is the idea that the world is a simulation running inside a computer. But Leibniz's idea was more like that there is an arbitrarily large number of computers running the same simulation, while some of them also run artificial intelligences which just watch the simulation unfold.
Which is an idea I think can be fairly described as "completely nuts".
> But Leibniz's idea was more like that there is an arbitrarily large number of computers running the same simulation, while some of them also run artificial intelligences which just watch the simulation unfold.
I think this was just Leibniz awkward attempt at explaining modal realism. The idea of many possible worlds is much more mainstream now in physics, so I wouldn't call it "completely nuts".
I think this was just Leibniz awkward attempt at explaining modal realism. The idea of many possible worlds is much more mainstream now in physics, so I wouldn't call it "completely nuts".
I wasn't previously acquainted with the term "modal realism" (been avoiding contemporary philosophy for a while now), but there doesn't seem to be an immediate connection in this case. There aren't actually many worlds being simulated here, as each computer simulates the same world and they all get the same results. Leibniz does introduce the idea of many possible worlds (§53), but as a set of designs for this whole thing (computers plus the stuff running inside them) from which God draws one particular design to be the actual world.
He might be closer to modal realists in other regards, though. I don't know.
He might be closer to modal realists in other regards, though. I don't know.
So I too love the idea that we don't need dark matter to explain all the gravitational effects we observe in the universe. However, is it just me or does the falsification of this seem a bit sketchy: if we find a dark matter particle...then my theory is false. That's a bit like saying...oh yeah if we find a different way to unify general relativity and quantum mechanics...then String Theory is false. It seems like there should be a 'smaller' way to falsify it.
I think you will find all the models are false to a degree. A model is only an approximation of the real thing. Quantum mechanics and General relatively cannot both be right. The obvious answer is that they are both wrong.
A thought experiment of mine.
Assume that all possible hypothesis or theories (explanations in general) form part of an "explanation space." Some explanations are good (theories), some have no evidence (hypothesis) and some are false (we are riding a giant turtle). Given the number of false explanations, the overall space is infinite. Hypothesis spaces would be islands within the false explanation space, theories islands within hypothesis and the truth as a single point within one of those theory spaces.
The question is, does that mean that the theory space is infinite? If so, that would mean that it would be impossible to know that we've found the truth (as a single point within this infinite space) - we'd only ever be able to conclude that we've found a closer approximation. Scientists may never run out of work.
Assume that all possible hypothesis or theories (explanations in general) form part of an "explanation space." Some explanations are good (theories), some have no evidence (hypothesis) and some are false (we are riding a giant turtle). Given the number of false explanations, the overall space is infinite. Hypothesis spaces would be islands within the false explanation space, theories islands within hypothesis and the truth as a single point within one of those theory spaces.
The question is, does that mean that the theory space is infinite? If so, that would mean that it would be impossible to know that we've found the truth (as a single point within this infinite space) - we'd only ever be able to conclude that we've found a closer approximation. Scientists may never run out of work.
Your "explanation space" is almost certainly infinite and mostly empty.
The closer any model approaches reality, the more it is indistinguishable from the object being described. Like any map, it becomes unwieldy with increased accuracy. The model becomes the size of the universe. So, a universe-sized model inside of an infinite explanation space?
The closer any model approaches reality, the more it is indistinguishable from the object being described. Like any map, it becomes unwieldy with increased accuracy. The model becomes the size of the universe. So, a universe-sized model inside of an infinite explanation space?
>The question is, does that mean that the theory space is infinite? If so, that would mean that it would be impossible to know that we've found the truth (as a single point within this infinite space) - we'd only ever be able to conclude that we've found a closer approximation. Scientists may never run out of work.
The theory space is definitely infinite, in either the interesting sense of something like "the space of all possible programs, treated as causal or directed-generative models" or in the trivial sense that you can take any simple, well-supported theory and come up with mathematical elaborations that don't change any of the pre-existing empirical predictions.
In a certain sense, "the truth" may constitute an infinitely small point in a space that's more continuous than discrete.
The theory space is definitely infinite, in either the interesting sense of something like "the space of all possible programs, treated as causal or directed-generative models" or in the trivial sense that you can take any simple, well-supported theory and come up with mathematical elaborations that don't change any of the pre-existing empirical predictions.
In a certain sense, "the truth" may constitute an infinitely small point in a space that's more continuous than discrete.
Isn't that just relativistic quantum field theory?
that's the thing, gravity from GR doesn't quantize well, or actually at all.
Einstein gravity quantizes remarkably well in the weak field limit; it's called perturbative quantum gravity, and is considered (with good reason) a sound effective field theory (in the Kenneth G Wilson sense of "effective"). One of the results of perturbative quantization is the discovery of the non-renormalization -- by power-set counting -- of gravity and why (very roughly and simply, it's because gravity is a long-range and self-interacting force). However, this only matters in systems where you would need to use Feynman diagrams involving multiple loops of gravitons, which essentially defines strong gravity, and you'll only find that well inside the event horizons of black holes, or in the extremely early big bang universe.
Outside the strong gravity limit, perturbative quantization of Einstein gravity exactly corresponds with General Relativity, as indeed any theory seeking to extend or replace General Relativity pretty well must (since GR accords with so much observational and experimental evidence).
There is also little reason to expect that we will never arrive at methods other than power-set counting to deal with the explosion of variables in many-loop systems, although that in itself should not preclude investment in other quantum gravity programmes that are very different.
Outside the strong gravity limit, perturbative quantization of Einstein gravity exactly corresponds with General Relativity, as indeed any theory seeking to extend or replace General Relativity pretty well must (since GR accords with so much observational and experimental evidence).
There is also little reason to expect that we will never arrive at methods other than power-set counting to deal with the explosion of variables in many-loop systems, although that in itself should not preclude investment in other quantum gravity programmes that are very different.
> "So I too love the idea that we don't need dark matter to explain all the gravitational effects we observe in the universe."
It is an attempt to explain. Just like an attempt to explain (prediction) of Higgs Boson. It was only true once we observed it via experimentation.
Falsification makes sense if the theory has been experimentally validated. You can't falsify something that has not been proven.
There is no one claiming String theory or the theory discussed here is true - no experimental evidence has been produced.
It is an attempt to explain. Just like an attempt to explain (prediction) of Higgs Boson. It was only true once we observed it via experimentation.
Falsification makes sense if the theory has been experimentally validated. You can't falsify something that has not been proven.
There is no one claiming String theory or the theory discussed here is true - no experimental evidence has been produced.
Remember that these people use a language that might sound similar to common english, but words have different meaning and it is much more precise. No reading between the lines.
He gave an example of what would falsify his theory, that is all.
He gave an example of what would falsify his theory, that is all.
In the summary, it says that these theories are "best understood in Anti de Sitter space...". I thought current observations ran against a spacetime that had a negative curvature. Are they just saying the math is easier in that geometry, but that it still applies to flat (or ever-so-slightly-positively curved) spacetime? Or are they arguing in favor of a "saddle-shaped" universe?
Spacetime has a positive cosmological constant, so it's closer to de-Sitter than Anti de-Sitter. It doesn't really have to do with curvature exactly, which is given by the Riemann tensor (so it doesn't make sense to say it's positive/negative).
But you certainly can talk about curvature scalars being positive/negative which are derived from the Riemann tensor.
The ADS in 'ADS/CFT correspondence' stands for 'anti-de Sitter'. Any time you read someone talking about 'information on the boundary' of a bulk space, that's usually what they're working with.
I'm sure there's a way to transform everything to a de Sitter space, but i'm neither a mathematician nor a physicist, so I don't know how it's done...
I'm sure there's a way to transform everything to a de Sitter space, but i'm neither a mathematician nor a physicist, so I don't know how it's done...
How about Dark Meat? I like Dark Meat.
Discussion in Dutch: http://www.volkskrant.nl/wetenschap/ineens-klopt-het-univers...
To what degree does this contradict Einstein's theory of gravity?
It does not contradict Einstein's theory of gravity, just as Einstein did not contradict Newton. All three are different models explaining progressively more thorough levels of observation.
Don't think of a theory so much as "what is true" but rather as a set of propositions and equations which are designed to model the way physical processes are observed to occur.
Theories exist within their own provenance of observation. Both Einstein and Newton's theories reflect reality within certain limits, but outside those limits they do not. To allow Einstein's theory to apply at larger scales, we proposed dark matter because Einstein could not account for the behavior of galaxies unless there was some hidden element involved. Thus we proposed dark matter. It is a reasonable accommodation, but one that has defied confirmation.
The emergent theory embraces both Newton and Einstein, eliminates any need for dark matter, and attempts to explain all current observations within a single framework.
Einstein's theory made testable predictions which were later proven to be true. The emergent theory lacks such confirmation, and so time will tell whether it reflects reality.
Don't think of a theory so much as "what is true" but rather as a set of propositions and equations which are designed to model the way physical processes are observed to occur.
Theories exist within their own provenance of observation. Both Einstein and Newton's theories reflect reality within certain limits, but outside those limits they do not. To allow Einstein's theory to apply at larger scales, we proposed dark matter because Einstein could not account for the behavior of galaxies unless there was some hidden element involved. Thus we proposed dark matter. It is a reasonable accommodation, but one that has defied confirmation.
The emergent theory embraces both Newton and Einstein, eliminates any need for dark matter, and attempts to explain all current observations within a single framework.
Einstein's theory made testable predictions which were later proven to be true. The emergent theory lacks such confirmation, and so time will tell whether it reflects reality.
>Einstein's theory made testable predictions which were later proven to be true. The emergent theory lacks such confirmation, and so time will tell whether it reflects reality.
The author claims to be making a few novel predictions which, he claims, astronomers can go check. He also retrodicts several things we observe, though I'm not enough of a physicist to say if he's using a simple enough model for that to be interesting.
The author claims to be making a few novel predictions which, he claims, astronomers can go check. He also retrodicts several things we observe, though I'm not enough of a physicist to say if he's using a simple enough model for that to be interesting.
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How does the theory explain unaccountable 96% of the universe which we cannot observe/detect? Is there a thing such as antibaryonic matter?
> The central idea of this paper is that the volume law contribution to the entanglement
entropy, associated with the positive dark energy, turns the otherwise “stiff” geometry
of spacetime into an elastic medium. We find that the elastic response of this ‘dark
energy’ medium takes the form of an extra ‘dark’ gravitational force that appears to
be due to ‘dark matter’.
Does this in any way match with Lipinski's gravity discussion (http://adsabs.harvard.edu/abs/2008AcPPB..39.2823L) that was mentioned here just recently (unifiedgravity.com)?
Does entropic gravity explain the lensing phenomenon attributed to dark matter?
I do not understand this stuff, but the connection between gravity and horizont sounds like this [quantized acceleration theory](http://physicsfromtheedge.blogspot.de/)
Dark matter is so deeply embedded into cosmology and modern astrophysics, you would have to explain a host of solidly observed phenomena to be a compelling alternative (baryon acoustic oscillations, the cosmic microwave background, primordial abundances, the evolution of structure or the "cosmic web"). Comparing to those things would probably take man-decades of work and also require computationally expensive cosmological simulations on super computers, so I'm skeptical we will see the kind of theoretical/observational comparison that would make you sit up and take notice.
[1] https://en.wikipedia.org/wiki/Bullet_Cluster