Erik Verlinde's new view on dark matter

[MTd2]

UPDATE: New Paper discussion starts here: https://www.physicsforums.com/threads/erik-verlindes-new-view-on-dark-matter.755235/#post-5615947

This is all I could gather from abstracts of talks and colloquiums he gave this year. Each of them have a different bit of information

******************

String Theory and the Entropic Origin of Gravity, Dark Energy and Dark Matter
II Tuscan Meeting on Theoretical Physics. Feb 25th

Erik Verlinde (Amsterdam U.)
Abstract:
Recent developments indicate that quantum entanglement and its associated entropy play a central role in explaining the connectivity of space time and the origin of gravity. In string theory a concrete mechanism for the quantum entanglement of space time is provided by the so-called long string phenomenon. In a cosmological setting these entangled long strings form a dynamical system whose energy can be identified with the dark energy. Using an accurate analogy with entanglement network of polymers, we calculate the effects due to slow relaxation processes and find excellent quantitative agreement with the phenomena attributed to dark matter in galaxies, clusters of galaxies, and the cosmos.

***************************

In Arizona State University Department of Physics, January 30th

Recent developments indicate that quantum entanglement and its associated entropy play a central role in explaining the connectivity of space time and the origin of gravity. String theory provides a concrete mechanism of the quantum entanglements of the underlying microscopic degrees of freedom. In a cosmological setting these degrees of freedom form a dynamical system whose energy can be identified with the dark energy of our universe. The usual laws of gravity, which are derived from the first law of thermodynamics, are valid in an adiabatic approximation. Using an accurate analogy with entanglement network of polymers, I show that the slow relaxation processes are responsible of the phenomena attributed to dark matter. These considerations lead to a universal formula for the dark matter distribution in galaxies, clusters of galaxies, and the cosmos, which agrees extremely well with observations.

https://www.facebook.com/ASUPhysics...1599517534789/767592219935515/?type=1&theater

******************************

The Entropic Origin of Gravity, Dark Energy and Dark Matter
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UserErik Verlinde (Amsterdam)
ClockWednesday 21 May 2014, 14:15-15:15
HouseMR2, Centre for Mathematical Sciences.
If you have a question about this talk, please contact Dr Joan Camps.

Recent insights from black hole physics, string theory and the AdS/CFT correspondence suggest that gravity is an emergent phenomenon. The microscopic counting of black hole states together with the recently found connection between gravity and quantum entanglement give important clues towards the underlying mechanism. Motivated by these ideas I propose that space-time can be viewed as an entanglement network of “long strings”. Anti-de Sitter and de Sitter space correspond to the distinct situations in which these “long strings” are all in their ground state or all in an excited state. By using an analogy with entanglement networks of polymers, I show that this description leads to memory effects that quantitatively describe the observed phenomena attributed to dark matter.

**********************String Theory and the Entropic Origin of Gravity, Dark Energy, and Dark MatterDepartment Colloquia
Spring 2014
Erik Verlinde
Affiliation: University of Amsterdam
Seminar Date: Thu, 01/30/2014 - 3:15pm - 4:15pm
Location: PSF 101
Host:
Maulik Parikh
Abstract

Recent developments indicate that quantum entanglement and its associated entropy play a central role in explaining the connectivity of space time and the origin of gravity. String theory provides a concrete mechanism for the quantum entanglement of the underlying microscopic degrees of freedom. In a cosmological setting these degrees of freedom form a dynamical system whose energy can be identified with the dark energy of our universe. The usual laws of gravity, which are derived from the first law of thermodynamics, are valid in an adiabatic approximation. Using an accurate analogy with entanglement network of polymers, I show that the slow relaxation processes are responsible for the phenomena attributed to dark matter. These considerations lead to a universal formula for the dark matter distribution in galaxies, clusters of galaxies, and the cosmos, which agrees extremely well with observations.//////////////////////////////////////////////

It seems that the slow relaxation, with an analogy of a network of entangled polymers, of the phenomenon of "long strings", which lead to a formula of dark matter distribution, which agrees extremely well with observations.

 

[craigi]

In string theory, gravity is a fundamental force and not an entropic force, so how can he use string theory with an argument that gravity is entropic in nature?

 

[mitchell porter]

In string theory, gravity is a fundamental force and not an entropic force, so how can he use string theory with an argument that gravity is entropic in nature?

In his talks, Verlinde sometimes appeals to open-closed string duality, which sort of refers to all the string-theory consequences of the fact that a cylinder is a circle times a line segment. In general, a graviton is a closed string (circle) and a gauge boson is an open string (line segment). So a cylinder can be seen as a closed string evolving along a time interval (the line segment), or as an open string evolving around a time loop (the circle). This is apparently the geometric basis of a number of known relations between gauge field theories and gravity. Verlinde wants to use it too but I can't tell you how.

Something I'd like to know, is whether it ever makes sense to have an entropic force in which the entropy is a von Neumann entropy, the definition of entropy for a quantum state. Back when I was trying to make sense of Verlinde's talks (they have not been turned into a paper yet), my intuition said that maybe he needed a "quantum entropic force", if there is such a thing. But I never reasoned it out myself.

 

[MTd2]

Mitchel, these are new views. I am not sure how they represent his old views. For example, he didn't talk about dark matter before.

 

[craigi]

Something I'd like to know, is whether it ever makes sense to have an entropic force in which the entropy is a von Neumann entropy, the definition of entropy for a quantum state. Back when I was trying to make sense of Verlinde's talks (they have not been turned into a paper yet), my intuition said that maybe he needed a "quantum entropic force", if there is such a thing. But I never reasoned it out myself.

I was just wondering myself, if the degeneracy pressure from the Pauli exclusion principle, would be well represented as an entropic force.

 

[member 11137]

You certainly did "google" that article on Wikipedia
http://en.wikipedia.org/wiki/Entropic_gravity
E. Verlinde's theory is cited.
There are many references at the end of the text.

 

[Chronos]

I would call this a 'weak string' view of gravity. It seems to make sense.

 

[kodama]

Emergent Gravity and the Dark Universe
Erik P. Verlinde
(Submitted on 7 Nov 2016 (v1), last revised 8 Nov 2016 (this version, v2))
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional `dark' gravitational force describing the `elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a_0 =cH_0, and provide evidence for the fact that this additional `dark gravity~force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
Comments: 5 figures
Subjects: High Energy Physics - Theory (hep-th)
Cite as: arXiv:1611.02269 [hep-th]

 

[PeterDonis]

Back in 2010, when Verlinde published an earlier paper along the same lines, neutron interferometry experiments were cited as evidence against an entropic model of gravity, as explained for example here:

http://motls.blogspot.nl/2010/01/erik-verlinde-why-gravity-cant-be.html

I don't know if these criticisms are still relevant to this latest paper, but it looks to me like they should be.

 

[Demystifier]

Gravitational force is reversible. (Think of elliptic planet trajectories that, in the absence of other forces, can last forever.)

Entropic force is not reversible. (You need an external force if you want to separate objects that were attracted by the entropic force.)

How about that?

 

[RockyMarciano]

Back in 2010, when Verlinde published an earlier paper along the same lines, neutron interferometry experiments were cited as evidence against an entropic model of gravity, as explained for example here:

http://motls.blogspot.nl/2010/01/erik-verlinde-why-gravity-cant-be.html

I don't know if these criticisms are still relevant to this latest paper, but it looks to me like they should be.

I think they are since the idea of entropic gravity and entanglement entropy is at the root of his new paper too. But it is debatable if the criticism based on the the lack of the loss of the interference pattern at a distance in presence of gravity is convincing. It seems like a question of degree in Verlinde's view and the influence of entropy in the neutron experiments would be too small, while in the link interference patterns is treated in simple absence/presence terms.

Gravitational force is reversible. (Think of elliptic planet trajectories that, in the absence of other forces, can last forever.)

Entropic force is not reversible. (You need an external force if you want to separate objects that were attracted by the entropic force.)

How about that?

The classical Newtonian view of gravitational force is certainly as a reversible force. But already GR's treatment of gravity is not exactly reversible, for instance using your own example of the elliptic orbits, the Einsteinian correction makes them open, the ellipses cannot close due to curvature, and that is not exact reversibility in the Newtonian sense. Actually the very idea of variable curvature to explain gravity departs from reversibility.

I think Verlinde's point(to get into his new paper proper) is more defendible phenomenologically than conceptually from what he writes. He is basically saying GR is wrong and yet he is still borrowing concepts from Einstein's GR, like the irreversibility inherent to curvature, and the entropy from black holes, although to be fair the connection with black hole thermodynamics is limited to the analogy between galactic dynamics entropy in de Sitter cosmology and the formula for bh entropy as shown in the inequalities 1.3 and 1.4 of the linked paper. So it looks more like a justification of his new approach to cosmologic phenomenology than anything else.

 

[Demystifier]

But already GR's treatment of gravity is not exactly reversible, for instance using your own example of the elliptic orbits, the Einsteinian correction makes them open, the ellipses cannot close due to curvature, and that is not exact reversibility in the Newtonian sense. Actually the very idea of variable curvature to explain gravity departs from reversibility.

I don't understand that argument. Fine, in GR the trajectories are not ellipses. But if you reverse the velocity at some point, the trajectory will be the reverse of the original trajectory, which is reversible dynamics in the Newtonian sense. Moreover, the scalar curvature $R$ of GR does not change if you make the transformation $x^0\rightarrow -x^0$, so curvature is time-inversion invariant.

One might argue that at least black holes are irreversible in GR, because once you are in the hole you cannot escape out. But even that is, strictly speaking, wrong. If you reverse all velocities at some point, the black hole will turn into a white hole, which is a time-inverted black hole. Of course, you cannot reverse all velocities in practice, but this is not forbidden in principle by general principles of GR.

If you write GR in the canonical Hamiltonian form, the Hamiltonian is strictly quadratic in canonical momenta, which is another way to see that GR is time-inversion invariant, i.e. reversible.

 

[haushofer]

Gravitational force is reversible. (Think of elliptic planet trajectories that, in the absence of other forces, can last forever.)

Entropic force is not reversible. (You need an external force if you want to separate objects that were attracted by the entropic force.)

How about that?

The paper states a modification of GR at certain cosmological lengthscales, so I guess that these extra terms introduce non-reversibility . but I could be wrong, still have to read it.

 

[martinbn]

One might argue that at least black holes are irreversible in GR, because once you are in the hole you cannot escape out. But even that is, strictly speaking, wrong. If you reverse all velocities at some point, the black hole will turn into a white hole, which is a time-inverted black hole. Of course, you cannot reverse all velocities in practice, but this is not forbidden in principle by general principles of GR.

They are irreversible because of the area theorem.

Also a trapped surface can form through evolution. Initial data that doesn't contain an trapped surface can have a maximal development that does contain a trapped surface. Not true in the time reversed situation. If the initial data doesn't have an anti-trapped surface it will not develop one.

 

[Demystifier]

They are irreversible because of the area theorem.

Also a trapped surface can form through evolution. Initial data that doesn't contain an trapped surface can have a maximal development that does contain a trapped surface. Not true in the time reversed situation. If the initial data doesn't have an anti-trapped surface it will not develop one.

I wouldn't say that those properties make GR irreversible. Otherwise, one could argue that even Newtonian mechanics of a free particle in 1 dimension is irreversible. (By free, I mean in the absence of forces.) Namely, if free particle moves to the left, then it can never start to move on the right. This is absolutely true for free Newtonian mechanics, yet we don't call it irreversibility.

So what is irreversibility? Reversibility is the property that f(t) is a solution if and only if f(-t) is also a solution. Irreversibility, of course, is the negation of reversibility.

In the case of GR, if a black hole is a solution, then the corresponding white hole is also a solution.

 

[martinbn]

Yes, but some solutions are considered not physical so they are excluded.

Your classical mechanics example is not completely analogous to the black hole case. A particle moving to the left can be made to move to the right. If something collapses to a black hole you cannot make it not a black hole.

 

[Demystifier]

Yes, but some solutions are considered not physical so they are excluded.

You think like a physicist, while I think like a mathematician. That cannot be good.

A particle moving to the left can be made to move to the right.

Not in the absence of forces.

If something collapses to a black hole you cannot make it not a black hole.

You can if you can violate positive-energy assumption, which you can by some quantum effects.

 

[RockyMarciano]

I don't understand that argument. Fine, in GR the trajectories are not ellipses. But if you reverse the velocity at some point, the trajectory will be the reverse of the original trajectory, which is reversible dynamics in the Newtonian sense. Moreover, the scalar curvature $R$ of GR does not change if you make the transformation $x^0\rightarrow -x^0$, so curvature is time-inversion invariant.

One might argue that at least black holes are irreversible in GR, because once you are in the hole you cannot escape out. But even that is, strictly speaking, wrong. If you reverse all velocities at some point, the black hole will turn into a white hole, which is a time-inverted black hole. Of course, you cannot reverse all velocities in practice, but this is not forbidden in principle by general principles of GR.

If you write GR in the canonical Hamiltonian form, the Hamiltonian is strictly quadratic in canonical momenta, which is another way to see that GR is time-inversion invariant, i.e. reversible.

It is easier than all that, we are dealing with GR in vacuum here, so no scalar curvature R, just Weyl curvature. It is hard IMO to argue that gravity in the relativistic Einsteinian local vacuum approximation around a source is not locally time-oriented(even if globally , being asymptotically Minkowskian is independent of time and hypersurface orthogonal) and therefore irreversible. Clearly a lightcone must be chosen locally if the Weyl curvature is to induce post-Minkowskian and post-Newtonian corrections.

 

[martinbn]

You think like a physicist, while I think like a mathematician. That cannot be good.

Well, not sure about that. The likes of Dirac don't exclude solutions and can give answers as -2 fish, where a mathematician wouldn't.

Not in the absence of forces.

Yes, but presence of forces isn't against the laws of nature.

You can if you can violate positive-energy assumption, which you can by some quantum effects.

Hm, you can shrink it, but will it go away completely? I am not even sure of QM violations of the energy conditions is enough.

 

[Demystifier]

Well, not sure about that. The likes of Dirac don't exclude solutions and can give answers as -2 fish, where a mathematician wouldn't.

By the way, negative number of fish (i.e. fish made of antiparticles) is OK for me, but when a physicist proposes negative probability, that is something I cannot digest. This is related to my general views on probability discussed in
https://www.physicsforums.com/threads/is-probability-theory-a-branch-of-measure-theory.890795/

Hm, you can shrink it, but will it go away completely? I am not even sure of QM violations of the energy conditions is enough.

Well, by Hawking radiation (which involves a flux of negative energy falling into the hole) the black hole evaporates completely, at least according to the semi-classical theory. On the other hand, perhaps you recall my own theory according to which Hawking radiation stops before the hole goes away completely ( https://arxiv.org/abs/1505.04088 ), but even in that alternative scenario the remaining object does not longer have a horizon, so nothing stops matter from escaping by "ordinary" mechanisms.

 

[Berlin]

New paper today in PRL of S.S. McGaugh et al (see http://physics.aps.org/) which looks like support for Verlinde. Verlinde also citates earlier papers from these people. They say that only accelaration is the relevant parameter, just like it seems with Verlinde. Dark matter is locally coupled to baryonic matter, if I understand it right. Needs more study though!

See also their arxiv: https://arxiv.org/pdf/1610.08981.pdf

berlin

 

[haushofer]

I think I would become more convinced if his theory can explain the Bullet Cluster. Still have to read the full paper though, I'm first trying to understand the developments leading to these ideas.

 

[Michael27]

A strict area law is known to hold in condensed matter systems with gapped ground
states. Indeed, we conjecture that from a microscopic bulk perspective AdS spacetimes
correspond to the gapped ground states of the underlying quantum system. The build-
ing blocks of de Sitter spacetime are, according to our second postulate, not exclusively
short range entangled, but also exhibit long range entanglement at the Hubble scale.
Again by analogy with condensed matter physics this indicates that these de Sitter
states correspond to excited energy eigenstates. Hence, the entanglement entropy con-
tains in addition to the area law also a volume law contribution. In terms of a tensor
network picture this means these states contain an amount of quantum information
which is evenly divided over all tensors in the network.

This quote from the paper mentions quantum information which is evenly divided over all tensors in the network. Does anyone have some reference or paper which explains to me how this information becomes evenly divided? Is this purely the timescale or is there more to it? How does this information propagate through the network? Like in the case entanglement is lost due to observation.
And I am assuming this network actually is the entire universe, is this correct?

 

[MTd2]

I think I would become more convinced if his theory can explain the Bullet Cluster. Still have to read the full paper though, I'm first trying to understand the developments leading to these ideas.

I think I can give a wave hand explanation On section 7.1, he gives the answer where dark matter is similar to elastic memory (I think a better analogy is a deformed plastic). In the bullet cluster, dark matter is ahead of the collisional gas. Since the elastic mass is really similar to a sort of rubber surface attached to a galaxy, where all its mass comes from tension, it will "detach" from each cluster of baryon mass, and accelerate faster towards each other.

 

[jamalkoiyess]

How can i understand his view as a 1st year physics student with no background in most of the topics discussed.

 

[martinbn]

How can i understand his view as a 1st year physics student with no background in most of the topics discussed.

Try to read the paper.

 

[haushofer]

I think I can give a wave hand explanation On section 7.1, he gives the answer where dark matter is similar to elastic memory (I think a better analogy is a deformed plastic). In the bullet cluster, dark matter is ahead of the collisional gas. Since the elastic mass is really similar to a sort of rubber surface attached to a galaxy, where all its mass comes from tension, it will "detach" from each cluster of baryon mass, and accelerate faster towards each other.

Thanks. I have to think about it still though.

 

[David Neves]

Watch Sean Carroll's video.



He explains that even if you accept the findings and results of the recent papers, we STILL NEED dark matter and dark energy to explain what we observe.

 

[ohwilleke]

He explains that even if you accept the findings and results of the recent papers, we STILL NEED dark matter and dark energy to explain what we observe.

Or not. Additional dark matter is needed in clusters for MOND and its relativistic extension TeVeS, but that is not the only modified gravity game in town, and I do not believe that TeVeS need dark energy as it, like general relativity, has a cosmological constant (which is a gravity modification) in lieu of a dark energy substance, that captures the observed acceleration of the expansion of the universe.

The galaxy cluster system Abell 1689 has been well studied and yields good lensing and X-ray gas data. Modified gravity (MOG) is applied to the cluster Abell 1689 and the acceleration data is well fitted without assuming dark matter. Newtonian dynamics and Modified Newtonian dynamics (MOND) are shown not to fit the acceleration data, while a dark matter model based on the Navarro-Frenk-White (NFW) mass profile is shown not to fit the acceleration data below ~ 200 kpc.

- J. W. Moffat and M. H. Zhoolideh Haghighi, "Modified gravity (MOG) can fit the acceleration data for the cluster Abell 1689" (16 Nov 2016).

The introduction of this short paper observes that:

MOG has passed successful tests in explaining rotation velocity data of spiral and dwarf galaxies (Moffat & Rahvar (2013)), (Zhoolideh Haghighi & Rahvar (2016)), globular clusters (Moffat & Toth (2008b)) and clusters of galaxies (Moffat & Rahvar (2014)). Recently, it was claimed (Nieuwenhuizen (2016)) that no modified gravity theory can fit the Abell 1689 acceleration data without including dark matter or heavy (sterile) neutrinos. The cluster A1689 is important, for good lensing and gas data are available and we have data from 3kpc to 3Mpc. We will show that MOND (Milgrom (1983)) does not fit the A1689 acceleration data, nor does the dark matter model based on an NFW mass profile. However, MOG does fit the A1689 acceleration data without dark matter.

The conclusion of the paper notes:

The fully covariant and Lorentz invariant MOG theory fits galaxy dynamics data and cluster data. It also fits the merging clusters Bullet Cluster and the Train Wreck Cluster (Abell 520) without dark matter (Brownstein & Moffat (2007); Israel & Moffat (2016)). A MOG application to cosmology without dark matter can explain structure growth and the CMB data (Moffat & Toth (2013)). The fitting of the cluster A1689 data adds an important success for MOG as an alternative gravity theory without dark matter.

 

[haushofer]

Just curious: a lot of these approaches rely on weak field approximations. Could it be that because of that we're overlooking non-linear effects which could explain the data? I'm thinking in the spirit of e.g. monster/rogue-waves, caused by non-linear effects of the hydrodynamical equations underlying them.

Probably too naive, but just wondering :)

 

[ohwilleke]

Just curious: a lot of these approaches rely on weak field approximations. Could it be that because of that we're overlooking non-linear effects which could explain the data? I'm thinking in the spirit of e.g. monster/rogue-waves, caused by non-linear effects of the hydrodynamical equations underlying them.

Probably too naive, but just wondering :)

I think that it is highly likely that there are non-linear effects in weak fields that are giving rise to phenomena interpreted as modified gravity or dark matter, and that some of the non-linearities get ignored inappropriately because of simplifying assumptions that aren't justified or a failure to recognize how a very slight effect can have a cumulatively important consequence in large scale systems when a force is always attractive.

 

[PeterDonis]

Could it be that because of that we're overlooking non-linear effects which could explain the data? I'm thinking in the spirit of e.g. monster/rogue-waves, caused by non-linear effects of the hydrodynamical equations underlying them.

Do you have any references for this type of model being applied in cosmology?

I think that it is highly likely that there are non-linear effects in weak fields

Based on what theoretical model?

Everyone, please bear in mind the PF rules about personal speculations.

 

[ohwilleke]

A summary of some of the empirical data can be found, for instance, at Federico Lelli, et al., "One Law To Rule Them All: The Radial Acceleration Relation of Galaxies" (October 27, 2016). Examples models addressing this data or exploring non-linear extensions of GR include: J.W. Moffat and M.H. Zhoolideh Haghighi, "Modified gravity (MOG can fit the acceleration data for the cluster Abell 1689" (November 16, 2016); Borut Bajc and Francesco Sannino, "Asymptotically Safe Grand Unification" (October 30, 2016); Sascha Trippe, "Can Massive Gravity Explain the Mass Discrepancy - Acceleration Relation of Disk Galaxies?" (May 28, 2013); Sacha Trippe "A Derivation of Modified Newtonian Dynamics" (March 28, 2013) (using a massive graviton approach); Dagoberto Escobar, "Born-Infeld type modification of the gravity" (September 28, 2012, last revised November 5, 2012); Max I. Fomitchev, "Dark Matter and Dark Energy as Effects of Quantum Gravity" (September 7, 2010); M. Wellmann, "Gravity as the Spin-2 Quantum Gauge Theory" (March 6, 2001); Leonardo Modesto, "Tree Level Gravity - Scalar Matter interactions in Analogy with Fermi Theory of Weak Interactions using Only a Massive Vector Field"(January 4, 2004).

 

[haushofer]

Do you have any references for this type of model being applied in cosmology?
Based on what theoretical model?

Everyone, please bear in mind the PF rules about personal speculations.

All I'm saying is that when one applies the linear approximation, non-linear effects could possible give rise to phenomena one cannot account for without doing a full numerical analysis.

I don't see how remarks like this contradict PF rules.

 

[haushofer]

I was asked to give a 1-hour talk about it at my university for future physics teachers; in Holland, where I work, it was quite a media hype. Maybe I could turn the talk into an insight later on. Details are still not clear to me, which is not strange of course, but it is also nice to put the story into a historical context. E.g. regarding the question about Dark Matter whether the theory is incomplete, or the observation. As Carroll says, the first one is much cooler and more interesting for the media to speculate upon :P