# Verlinde's gravity basics

Gold Member
I started to go over Verlinde's paper (http://arxiv.org/abs/1001.0785) and I'm just not convinced of what he's doing from the start.

At (3.5), he is assuming there is a particle within one compton wavelength of the holographic screen. Saying this immediately seems to imply that the momentum has an uncertainty on the order of mc, making this particle relativistic. From this, we get F = ma. How is it that that doesn't seem strange? My line of thinking is that we have this particle localized to an uncertainty in the position corresponding to an uncertainty in the momentum that by itself is relativistic. So the actual momentum must be far beyond that. Then we bring in Unruh, something that is relativistic, and what pops out is F = ma, something that is non-relativistic. This seems strange. Can someone.... put my mind at ease as to why this isn't all that strange?

Dear Pengwuino, Verlinde's proposal is a combination of vague ideas/observations. It does not specifies the fundamental blocks of the theory, e.g. what are the states on the holographic screens, their dynamics etc. therefore, it is hard/impossible to precisely follow particular limits, e.g. quantum to classical limit, relativistic to non-relativistic limit etc.

Even with this ambiguous and i would say ad hoc derivation of the Newtonian law of gravity, Verlinde's proposal seems has serious troubles, see e.g. the discussion in one of the previous threads -- Gravity is not entropic force?

marcus
Gold Member
Dearly Missed
I started to go over Verlinde's paper (http://arxiv.org/abs/1001.0785) and I'm just not convinced of what he's doing from the start...

Dear Pengwuino, Verlinde's proposal is a combination of vague ideas/observations. It does not specifies the fundamental blocks of the theory, ...-- Gravity is not entropic force?

It's possible that Smolin's reworking of the proof in the context of LQG would shed some light on it for you. He does, after all, specify the states on the boundary.
LQG has a general entropy-area relation, as I recall. He will give some source on that. So you might have a look:
http://arxiv.org/abs/1001.3668
Newtonian gravity in loop quantum gravity
Lee Smolin
16 pages
(Submitted on 20 Jan 2010)
"We apply a recent argument of Verlinde to loop quantum gravity, to conclude that Newton's law of gravity emerges in an appropriate limit and setting. This is possible because the relationship between area and entropy is realized in loop quantum gravity when boundaries are imposed on a quantum spacetime."

Then there is Jacobson's original 1995 paper. Unquestionably rigorous. You don't have to rely on Erik Verlinde's presentation.
http://arxiv.org/abs/gr-qc/9504004
Thermodynamics of Spacetime: The Einstein Equation of State
Ted Jacobson
8 pages, 1 figure. Physical Review Letters 1995
(Submitted on 4 Apr 1995)
"The Einstein equation is derived from the proportionality of entropy and horizon area together with the fundamental relation $$\delta Q=TdS$$ connecting heat, entropy, and temperature. The key idea is to demand that this relation hold for all the local Rindler causal horizons through each spacetime point, with delta Q and T interpreted as the energy flux and Unruh temperature seen by an accelerated observer just inside the horizon. This requires that gravitational lensing by matter energy distorts the causal structure of spacetime in just such a way that the Einstein equation holds. Viewed in this way, the Einstein equation is an equation of state. This perspective suggests that it may be no more appropriate to canonically quantize the Einstein equation than it would be to quantize the wave equation for sound in air."

I'm not saying that Verlinde's presentation of the idea is right, or that if something essentially right underlies it, the Verlinde paper is anything more than approximation, and intuitive motivation.
All I want to say is, don't throw out the baby with the bathwater. Don't dismiss Jacobson's 1995 work just because you might not like Verlinde's popularization.

Dear Marcus,

Pengwuino asked the question about derivation of non-relativistic laws of inertia and gravitation in Verlinde's paper. This discussion is the most notable new physics input by Verlinde -- he claims that Newtonian force is not the potential but entropic force. Nothing of that sort follows from the Jacobson's work, although the formal derivation of the Einstein equation in both papers are essentially the same. One thing is the formal equation and another the physical meaning you attribute to it. Don't you think so?

I am not dismissing Jaconson's 1995 work, but i view it as a cute formal observation that lacks more fundamental ground for its understanding. Verlinde's attempt to find such a theoretical ground is wrong in my opinion.

Gold Member
I haven't looked into detail into Jacobson's paper but Verlinde's idea just seems flat out confusing. F=ma seems to be derived using the Unruh temperature. Ok, fine. However, an inertial observer does not see a temperature, but should see the particle or what have you being accelerated. I don't even need to think about holography, this seems wrong just at face value. I also have seen the Unruh temperature take a different form for an observer under a centripetal acceleration that would not allow you to recover F = ma using the same assumption for the form of the entropy. You would recover some multiple like $$ma/\sqrt 3$$, I forget exactly what it is. I feel like verlinde is making connections that aren't justifiable.

can't you absorb that 1/sqrt{3} into the definition of the inertial mass? :-). Verlinde did something like that with 2\pi factor in the Unruh temperature. :-)

marcus
Gold Member
Dearly Missed
...
I am not dismissing Jaconson's 1995 work, but i view it as a cute formal observation that lacks more fundamental ground for its understanding. Verlinde's attempt to find such a theoretical ground is wrong in my opinion.

You may know that (for whatever signif. it may or may not have ) Ted J is one of the fathers of LQG. I think the first specifically Loop QG paper was by Jacobson and Smolin. Hve to check tht. Even before Rovelli got in. Ted has also played a valuable role as a Devil's Advocate and workshops/conferences, keeping people on their toes and poking holes.

Maybe tht's irrelevant. Be that as it may.

Anyway your reaction (aside for trivial differences in tone) strikes me as quite similar to what I've heard was the attitude of informed people in the LQG community back in the 1990s. That is, obviously this is a piece of mathematics. It shows there could be some deep physics connection. But it gives no hint what that could be.

so for years people thought of this as potentially significant but couldn't tell what to make of it.

Maybe it is something every QG physicist should have written on a postit piece of paer and have stuck up on his study/office wall. Feynman suggested a similar thing for why alpha is 1/137

========================
From a longer perspective I think the faults of Verlinde's popularization are irrelevant. What yu or I think of it is mostly cocktail conversation. Criticising Verlinde doesn't settle anything. The popularization could be weak and the idea still be good.
He makes lots of impulsive assumptions and approximations. If you don't like it this does not matter AFAICS. Just my humble opinion.
It's humanly interesting that here is a former prominent string-guy suddenly bitten by the entropic gravity bug.
=========================

But you could try criticising SMOLIN's paper. He does offer "building blocks". The argument is still partly intuitive and approximate, but there is some underlying physics hardware specified. So there is something to get your teeth into. Maybe it is bad, maybe good. Maybe you could determine that it is logically self-contradictory---I think that would be interesting.

The paper has about 50 cites as of today.

Anyway I hope we don't just beat up on Verlinde because he is an obvious target. Maybe you can try beating up on Smolin and see if he offers more resistance.

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You may know that (for whatever signif. it may or may not have ) Ted J is one of the fathers of LQG. I think the first specifically Loop QG paper was by Jacobson and Smolin. Hve to check tht.

I have great respect to Ted Jacobson as a physicist, and now since i know that he had quit LQG quickly i have even greater respect :-)

marcus
Gold Member
Dearly Missed
Since you have such great respect (as I do myself) for Ted J, here is the paper:
Nonperturbative Quantum Geometries.
Ted Jacobson, (Brandeis U. & UC, Santa Barbara) , Lee Smolin, (Yale U. & Santa Barbara, KITP) . YTP-87-29, BRX-TH-232, NSF-ITP-87-104, Jul 1987. 61pp.
Published in Nucl.Phys.B299:295,1988.
To date it has 206 cites.
There is a scanned KEK copy available online

Thanks marcus. But you are not suggesting that there is a hidden link between 1988 and 1995 papers, are you?

BTW, I had a brief look at Smolin's paper you have quoted earlier. if this is the only way to obtain Newton's law in LQG than all the criticisms of Verlinde's work is almost automatically applied to LQG. Hope, it is not that bad for LQG...

marcus
Gold Member
Dearly Missed
if this is the only way to obtain Newton's law in LQG​
Why assume that? Don't you know about the graviton propagator papers? Classical and semiclassical limits are longterm projects that make regular progress. I certainly don't think Smolin said "only way" so why would you make up that idea? Could you suffer from an irrational prejudice?

But you are not suggesting that there is a hidden link between 1988 and 1995 papers, are you?​
Did I make such a suggestion? No. You are the one "making suggestions".
What link could there possibly be besides that it is that same person with the same network of friends and colleagues.
Since you are an admirer of Jacobson, you say, you might enjoy this discussion by Jacobson Marolf and Rovelli.
http://arXiv.org/abs/hep-th/0501103
As I recall, Ted J played a major role in the first Loops conference, Loops 2004, which Rovelli organized at Marseille. Then a month later, at another southern France event, he had this trialogue about black hole entropy with Don Marolf and Carlo Rovelli.

In 2007 he posted a paper about renormalization and LQG black hole entropy. It raised extremely interesting questions IMHO which are only beginning to be answered.

Presumably other groups besides the LQG folks have benefitted from TJ talent for asking deep questions that could make someone think off and on for years about them. All I know is LQG case, they have benefitted a lot.

So if you want a "link" between some human research history going back many years, I can think of one. TJ is in close contact with the LQG people (going back to 1988) and in 1995 he discovers an intriguing connection between thermodynamics and gravity. This riddle gets planted in Smolins mind. Then in 2010, a week or so after Verlinde paper, Smolin posts a LQG explanation. I think he must have been thinking about it off and on for 10 years!

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marcus
Gold Member
Dearly Missed
It's been fun yakking with you Chiko, but actually Penqwuino's question was focused on Verlinde.

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This is the quote from Smolin's paper you have brought in this thread:

"Previously it has been shown that the theory has massless spin two
excitations[12], which have the correct propagators in the low energy limit[13], but there has not before been a direct demonstration that the theory has a limit which yields Newtonian gravity." -- That is to say, according to Smolin his entropic derivation of Newtonian limit of LQG is the only one currently available. Very bad for LQG, if so.

If you were not suggesting link between earlier LQG paper by Jacobson and verlinde's paper, what was the point of bringing in the Jacobson's paper here?

Moreover, you may be interested in this article: http://www.deccanherald.com/content/82431/a-scientist-takes-gravity-causes.html. Concerning the Verlinde's entropic gravity idea the author quotes T. Jacobson:
''Dr Jacobson said he couldn’t make sense of it.''(Verlinde's work)

If the quotation in the article is accurate then it simply follows that even if Jacobson has been thinking about these things for 10 years, those thoughts were not the once of Verlinde and Smolin.

It's been fun yakking with you Chiko, but actually Penqwino's question was focused on Verlinde.

Exactly!

atyy
I started to go over Verlinde's paper (http://arxiv.org/abs/1001.0785) and I'm just not convinced of what he's doing from the start.

At (3.5), he is assuming there is a particle within one compton wavelength of the holographic screen. Saying this immediately seems to imply that the momentum has an uncertainty on the order of mc, making this particle relativistic. From this, we get F = ma. How is it that that doesn't seem strange? My line of thinking is that we have this particle localized to an uncertainty in the position corresponding to an uncertainty in the momentum that by itself is relativistic. So the actual momentum must be far beyond that. Then we bring in Unruh, something that is relativistic, and what pops out is F = ma, something that is non-relativistic. This seems strange. Can someone.... put my mind at ease as to why this isn't all that strange?

These guys found it strange too, for the same reasons. http://arxiv.org/abs/1003.1998

marcus
Gold Member
Dearly Missed
These guys found it strange too, for the same reasons. http://arxiv.org/abs/1003.1998

That's a great cite because on page 3 they run down (as you say) pretty much the same list of weaknesses as Pengwuino gave!

They aren't saying that the idea is wrong. Only that Verlinde's construction is dubious and his argument flawed. Modesto Randono in fact present a strong consistency check supporting the view that the idea might be right!

Interesting paper. It's been out less than a year and has 27 cites already.

===================
in their page 3 crit of Verlinde's argument they mention the Compton wavelength (just as Pengw. did) and then continue:
A potentially more serious objection to the construc- tion revolves around the peculiar combination of non-relativistic and relativistic concepts. More specifically, the definition of the surface S appear to be, at present, ill-defined. From assumption (ii) the energy of the surface is the energy associated with the rest mass of the source mass M, suggesting that the surface is fundamentally connected with the source mass. This in itself is potentially a problem since, in the non-relativistic scenario, typically the thermodynamic free-energy only consists of energies above the rest mass energy. Barring this rather weak objection, it is natural to think of the surface S as a horizon associated with the mass M, and many of the properties ascribed to this surface are properties that one would only expect from a horizon, including assigning the rest mass energy Mc2 to the surface. However, since the construction is intrinsically non-relativistic there is no obvious horizon present in the physical scenario...​

After a whole page explaining why Verlinde's case is so flawed and weak, they get to the point of saying why not just abandon the idea of a connection between gravity and entropy?

Faced with these difficulties one may be tempted to abandon the entropic picture of gravity as a mere coincidence, perhaps stemming from consistent dimensional analysis. Rather than attack these problems directly, we will offer a strong consistency check of the construction, and a simple model whereby plausible deviations to Newton’s law can be obtained by tweaking Verlinde’s procedure. This should serve to strengthen the viability of the model of gravity as an entropic force, but should also be viewed as a call to the community to strengthen the arguments employed in the construction....​

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I'm not sure how much better anyone can do without going deeper and try to understand also the origin and proper meaning of the holographic principle itself.

I like Verlindes paper, but it leaves alot still unclear. But no papers has ever yet solved all questions, so I see it as an interesting reflection.

I am a huge fan and firm believer that ALL interactions can be seen as entropic expectations, but not in terms of a classical probability, but "entropic" in terms of some not yet understood logic. In particular when we note that there are connections between actions (subject to variational principles), can be viewed as closely related to "relative entropy", this is clear in classical probability, in the quantum logic it's not yet complete understand. But I think there are also theoretical/logical reasons (apart from jacobsson etc) to see how generic interactions are related to generalized inference. Which in the classical case would be simply be max ent related.

All these things of jacobsson and including verlinde I still just see as reflections upon hints.

It's easy to find imperfections in most papers I think, but my personally impression from me on verlindes paper is that it's more worth reading that the average paper. So any critique should IMO be constructive, and suggest howto improve the deeper vision. Just pointing out things to object to is neither difficult nor constructive, except of course if you are in a competing camp. Then there is a point is simply showing that he is wrong, even though it does not improve anything.

/Fredrik

I
I am a huge fan and firm believer that ALL interactions can be seen as entropic expectations, but not in terms of a classical probability, but "entropic" in terms of some not yet understood logic.

Dear Fredirik, I hope you agree that scientific and religious believes are two very different and largely incompatible things. Do you have any evidence that supports your strong belief in "entropic everything"? In fact, all the theoretical and experimental knowledge accumulated so far in physics tells us that this kind of belief is incorrect.

Back to the 19th century people realized that fundamental forces (electric and gravitational) known at that time are potential forces. This notion of potential transformed/generalized into a notion of quantized field in the relativistic quantum field theory, which brilliantly describes HUGE amount of observational data. Inevitable prediction of these theories is the existence local degrees of freedom, e.g. photons, which have been observed in experiments. None of these and many other results follow from the "entropic" theories by definition.

Due to Holographic Principle the space has to emerge as an information background due to a program writen in a matrix on a screen. It creates the space with a different density of the interferences. The rest mass particle is defined by more interferences than the vacuum only.
I assume each interference (relation between the information) has encoded a constant time dilation = Planck time. Therefore close to massive object are more interferences and more time dilation. Therefore each particle will perceive a time dilation toward the massive object. We call it will follow the geodesic of the space.

On the other side each interference causes an oscillation and increases the velocity of the particle. Therefore it accelerates toward the massive object because there are more interferences (relations between the Compton wavelength of the particles).

May be it would be a solution why the particle gravitate toward the higher entropy as a space with higher amount of the interferences.

Dear Fredirik, I hope you agree that scientific and religious believes are two very different and largely incompatible things.

Religion has nothing whatsover to do with what I said. I just want to first not that. Human religion and rational degrees of beleifs in the context of inductive reasoning are very different things. If you confuse what I tried to sy with religion it's either because you really didn't get any of what I tried to convey - or probably more likely - my incompetence in conveying deep ideas in a simple way.

For example. Ask a string theorist what "evidence" that have, just rationally justifies investing 40 years of research? This is the belief I talk about - the belief is what justifies an action or endavour. One formalisation of that is inductive logic. Not huaman religion or other irrational beliefs. However degrees of beliefs are rightfully subjective. Each individual scientists has their own expectations; that rules his choice of questions and actions. This is just like it should be. This is rational.

Do you have any evidence that supports your strong belief in "entropic everything"?

Of course, but wether you see it, I can not ensure. First of all there are plenty of technical similarities between how physical systems are successfully described in terms of non-deductive inference: thermodynamics and statistics. Also the action formulation of all physics as dynamics beeing what minimizes or extremizes certain measures (be it ACTIONS or ENTROPY; in the dynamic resp static case). There are also strong similarities with the structure of QM, with normal statistics, it's just this additional thing with quantum logic that's not understood. And then we have the coincidence that Einsteins equations seems to look like a thermodynamic equation of state. (ie it corresponds to an equilibrium condistion). Also several peopla have (although not to my personal satisfaction but still) presented different forms of "derivations" of quantum logic as the only consistent way to make rationa linference based on qualifieers beeing compelx numbers. (See for example Ariel Caticha, but there are others working on such "inference physics" don't have them all on top of my head). ET Jaynes is one who in this book "probability theory - the logic of science", argues that probability is a unique inductive inference that follows from trying to formalize a framework for rating "degrees of beliefs". Of course he uses real numbers, not complex ones.

But aside of tons of such connections and unlikely conicidences the major reason for me is that the very nature of science, requires that it adheres to rational reasoning. Science is not a deductive process, it's a learning process, which is exactly what inference is.

Entropic origin of actions, are fully in the spirit of rational action based upon rational inference. Science does not unravel truth, it rather just develops rational beleifs (ie. based on observational evidence supporting it) on what to expect.

Several tersm are synonmous here.

A belief ~ an expectation

Every prediction in QM takes the FORM of an statistical expectation. Degrees of beleifs are simply ~ something like the subjectively estimated confidence level.

Science ~ rational belief
Religion is more is irrational belief

(I'm not trying to pick on religious people here, just making a point)

None of these and many other results follow from the "entropic" theories by definition.

Sure, none of the actions we know are constructed this way. This is why this is radical indeed.

You are free to make your own judgements of course, which disagree with mine.

The inference perspective follows most strongly from the scientific learning process itself. If you have tried to reflect upon this, I think you should find that and inductive inference perspective does naturally suggest that all actions are due to the "statistics of evidence" and this yields an action that minimized the subjective information divergence, whis is the same as relative entropy. Entropy and action as measures, are very related if you look at the relation between transition amplitudes, information divergence and entropy in classical statistics. Action can be seen as an entropy in the state of histories. So the connection between the concept of entropy in the more general sense and action should be clear. This is not a fantasy. All this can be generalized. But it's complicated and am not done with it for sure. But that's beyond the point here, I'm merely defending the perspective which you seem to even mix up even with religion.

About the unification, I supposed maybe it's a bit naive of me to think I can convey that here without presenting more explicit things.

Anyway, without trying to be rude or anything, I do sincerely think that at least some people that totally dismiss the entropic origin of interaction simply doesn't understand the potential idea behind it.

One of my favourite quotes I learned about from one of Lee SMolins talks:

"People who appeal to fixed conceptions of necessity, contingency and possibility are simply confused"
-- Charles Sanders Peirce

/Fredrik

Religion has nothing whatsover to do with what I said. I just want to first not that. Human religion and rational degrees of beleifs in the context of inductive reasoning are very different things. If you confuse what I tried to sy with religion it's either because you really didn't get any of what I tried to convey - or probably more likely - my incompetence in conveying deep ideas in a simple way.

For example. Ask a string theorist what "evidence" that have, just rationally justifies investing 40 years of research? This is the belief I talk about - the belief is what justifies an action or endavour. One formalisation of that is inductive logic. Not huaman religion or other irrational beliefs. However degrees of beliefs are rightfully subjective. Each individual scientists has their own expectations; that rules his choice of questions and actions. This is just like it should be. This is rational.

Of course, but wether you see it, I can not ensure. First of all there are plenty of technical similarities between how physical systems are successfully described in terms of non-deductive inference: thermodynamics and statistics. Also the action formulation of all physics as dynamics beeing what minimizes or extremizes certain measures (be it ACTIONS or ENTROPY; in the dynamic resp static case). There are also strong similarities with the structure of QM, with normal statistics, it's just this additional thing with quantum logic that's not understood. And then we have the coincidence that Einsteins equations seems to look like a thermodynamic equation of state. (ie it corresponds to an equilibrium condistion). Also several peopla have (although not to my personal satisfaction but still) presented different forms of "derivations" of quantum logic as the only consistent way to make rationa linference based on qualifieers beeing compelx numbers. (See for example Ariel Caticha, but there are others working on such "inference physics" don't have them all on top of my head). ET Jaynes is one who in this book "probability theory - the logic of science", argues that probability is a unique inductive inference that follows from trying to formalize a framework for rating "degrees of beliefs". Of course he uses real numbers, not complex ones.

But aside of tons of such connections and unlikely conicidences the major reason for me is that the very nature of science, requires that it adheres to rational reasoning. Science is not a deductive process, it's a learning process, which is exactly what inference is.

Entropic origin of actions, are fully in the spirit of rational action based upon rational inference. Science does not unravel truth, it rather just develops rational beleifs (ie. based on observational evidence supporting it) on what to expect.

Several tersm are synonmous here.

A belief ~ an expectation

Every prediction in QM takes the FORM of an statistical expectation. Degrees of beleifs are simply ~ something like the subjectively estimated confidence level.

Science ~ rational belief
Religion is more is irrational belief

(I'm not trying to pick on religious people here, just making a point)

Sure, none of the actions we know are constructed this way. This is why this is radical indeed.

You are free to make your own judgements of course, which disagree with mine.

The inference perspective follows most strongly from the scientific learning process itself. If you have tried to reflect upon this, I think you should find that and inductive inference perspective does naturally suggest that all actions are due to the "statistics of evidence" and this yields an action that minimized the subjective information divergence, whis is the same as relative entropy. Entropy and action as measures, are very related if you look at the relation between transition amplitudes, information divergence and entropy in classical statistics. Action can be seen as an entropy in the state of histories. So the connection between the concept of entropy in the more general sense and action should be clear. This is not a fantasy. All this can be generalized. But it's complicated and am not done with it for sure. But that's beyond the point here, I'm merely defending the perspective which you seem to even mix up even with religion.

About the unification, I supposed maybe it's a bit naive of me to think I can convey that here without presenting more explicit things.

Anyway, without trying to be rude or anything, I do sincerely think that at least some people that totally dismiss the entropic origin of interaction simply doesn't understand the potential idea behind it.

One of my favourite quotes I learned about from one of Lee SMolins talks:

"People who appeal to fixed conceptions of necessity, contingency and possibility are simply confused"
-- Charles Sanders Peirce

/Fredrik

Dear Fredrik, I apologize if my reference to religion somehow offended you, but what I meant to ask is whether you firm belief in entropic origin of all interactions is based on some theoretical/experimental evidence, or it is just unjustifiable, and thus irrational expectation. Unfortunately, your long reply convince me that the later is the case.

You seems did not grasp the main point of my previous post -- A necessary requirement for any ''new theory'' to be considered as a possible adequate description of nature is that it must have a sensible limit were the experimentally verified "old theory" is reproduced. This is the case for all the established theories such as QED-Coulomb force, GR-Newtonian force. Even string theory, for your information, does it -- it has sensible quantum field theory limit.
I am afraid that you basic postulate of "entropic everything" fails do do so. We do observe photons after all!

Naive analogies you try to draw between entropy-action, statistical physics-QM are only formal. In essence these are very different notions: thermodynamical entropy is a quantity you can measure, while action is an unphysical object, just a tool to do physics. You can do the same physics without action (Hamiltonian formalism). Classical statistical and quantum expectations are also very different things -- "quantum logic", as you refer to it, gives different predictions from the classical statistics. You say we do not understand quantum logic -- actually we do! Moreover, it has been proven experimentally that "quantum logic" is the only correct one for microscopic phenomena.

I do not completely dismiss entropic origin of interactions -- there are entropic forces in nature, so are non-potential forces as well. All of them, however, are not fundamental forces. All those kind of forces observed so far can be derived (at least in principle) from more fundamental interactions which turns out to correspond to potential forces. There is no evidence in nature for the reverse logic.

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MTd2
Gold Member
A certain paper was written as a rebutal to Verlide's gravity.

http://arxiv.org/abs/1009.5414

The only comment it received was a brief half - paragraph of this paper, page 8, citation [25]:

http://arxiv.org/PS_cache/arxiv/pdf/1010/1010.4729v2.pdf

Notice that people are still taking Eric's gravity seriously. The latest citation was from Leonard Susskind:

http://arxiv.org/abs/1101.6048

It was a supportive citation, and in fact, Leonard wrote this paper because he was moved by Eric's ideas. See the conclusion of this paper.

A certain paper was written as a rebutal to Verlide's gravity.

http://arxiv.org/abs/1009.5414

The only comment it received was a brief half - paragraph of this paper, page 8, citation [25]:

http://arxiv.org/PS_cache/arxiv/pdf/1010/1010.4729v2.pdf

Notice that people are still taking Eric's gravity seriously. The latest citation was from Leonard Susskind:

http://arxiv.org/abs/1101.6048

It was a supportive citation, and in fact, Leonard wrote this paper because he was moved by Eric's ideas. See the conclusion of this paper.

Dear MTd2, It would be certainly better to judge on Verlinde's theory by using scientific arguments rather than citation count. But if you like to do so, let us look from another side:

The paper 1009.5414 is published in one of the leading peer-reviewed journals in high-energy physics, Physical Review D. Verlinde's original paper, after 1 year it first appeared in the arXiv is still not published. Moreover, among 152 citations Verlinde's paper received so far, only 45 are published, that is only third. If you take into account some of the published papers cite Verlinde's work but their actual content has nothing to do with entropic forces, the actual # of published paper supporting Verlinde's idea is even less.

The situation is indeed very strange: if the paper 1009.5414 is incorrect why nobody from the huge number of entropic gravity supporters have come up with a published paper that refutes the criticism. Instead, most of the papers seems to ignore 1009.5414 -- there is no logical explanation to this. This makes me to believe that the whole ''entropic story'', huge number of citations, media interest, 2 million European grant etc is more socio-political phenomenon rather than scientific. Therefore, my prediction is that this entropic buzz will die off in a year or two.

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A certain paper was written as a rebutal to Verlide's gravity.
Gravity is not an entropic force.
http://arxiv.org/abs/1009.5414

According to the experiments with ultra cold and slowly neutrons the entropy seems not to be a fundamental phenomenon. May be the most fundamental is the encoded quantum information which creates the quantum micro states. These microstates may interfere and the information (quantum superposition) has to be conserved.