Verlinde's gravity basics

  • Thread starter Pengwuino
  • Start date
  • #1
Pengwuino
Gold Member
5,009
17
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?
 

Answers and Replies

  • #2
CHIKO-2010
90
0
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?
 
  • #3
marcus
Science Advisor
Gold Member
Dearly Missed
24,757
790
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 [tex]\delta Q=TdS[/tex] 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.
 
  • #4
CHIKO-2010
90
0
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.
 
  • #5
Pengwuino
Gold Member
5,009
17
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 [tex]ma/\sqrt 3[/tex], I forget exactly what it is. I feel like verlinde is making connections that aren't justifiable.
 
  • #6
CHIKO-2010
90
0
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. :-)
 
  • #7
marcus
Science Advisor
Gold Member
Dearly Missed
24,757
790
...
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 :biggrin:) 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.
 
Last edited:
  • #8
CHIKO-2010
90
0
You may know that (for whatever signif. it may or may not have :biggrin:) 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 :-)
 
  • #9
marcus
Science Advisor
Gold Member
Dearly Missed
24,757
790
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
 
  • #10
CHIKO-2010
90
0
Thanks marcus. But you are not suggesting that there is a hidden link between 1988 and 1995 papers, are you?
 
  • #11
CHIKO-2010
90
0
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...
 
  • #12
marcus
Science Advisor
Gold Member
Dearly Missed
24,757
790
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? :biggrin:

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! :biggrin:
 
Last edited:
  • #13
marcus
Science Advisor
Gold Member
Dearly Missed
24,757
790
It's been fun yakking with you Chiko, but actually Penqwuino's question was focused on Verlinde.
 
Last edited:
  • #14
CHIKO-2010
90
0
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.
 
  • #15
CHIKO-2010
90
0
It's been fun yakking with you Chiko, but actually Penqwino's question was focused on Verlinde.

Exactly!
 
  • #16
atyy
Science Advisor
14,769
3,295
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
 
  • #17
marcus
Science Advisor
Gold Member
Dearly Missed
24,757
790
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....​
 
Last edited:
  • #18
Fra
3,619
369
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
 
  • #19
CHIKO-2010
90
0
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.
 
  • #20
czes
222
1
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.
 
  • #21
Fra
3,619
369
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
 
  • #22
CHIKO-2010
90
0
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.
 
Last edited:
  • #23
MTd2
Gold Member
2,028
26
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.
 
  • #24
CHIKO-2010
90
0
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.
 
Last edited:
  • #25
czes
222
1
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.
 
  • #26
Fra
3,619
369
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.

Of course, you are right. What I envision, as that are related to Verlindes entropic reasoning (but certainly not the exact same thing), is a research vision, and the solution is an open problem.

But to just line out, from my own intuitive picture, current physics will (IF the program is successful) be seen as equilibrium states. This is how what we currently thinkg are essential hardcoded laws of physics, but we don't konw WHY - will be understood as emergent from a deeper picture as equilibrium laws.

I fully share your view that a new theory must connect to the part of the current theory that is experimentally verified.

I am afraid that you basic postulate of "entropic everything" fails do do so. We do observe photons after all!

I admit that I don't see how observing photons is a counter argument? Local detector counts are in my picture more fundamental than the "photon is a particle". Local detector counts is one possible basis of the statistical evidence.

Also "entropic everything" isn't quite the precise postulate I use. Entropy is just s measure of the probability of a certain distribution in the set of possible distributions. So analysing this picture, "entropy" is not the central object to me, neither actio. What's central is subjective probabilities. But if you write down a transition probability, already in classical models like pulling balls from an urn, the expression contains information divergence that looks exactly like the we^-S, and S contains also shannon terms.

So I rather postulate something like "rational expectation", "rational action" that follow from a reconstruction of a discrete version of probabilit theory, that is based on counting evidence, BUT where the conditional probability is taken not wite respect to some classical prior, but with respect to a set of non-commuting counting records. which can be seen as product betweendifferent probability spaces, which have an overall normalisation to keep the total structure of constant count.

The only assoicaton to shannon entropy and actio I makare are remarkable formal similarities in the expressions. Because there appears naturally a weithging term as e^-Action in these expressions.

Then this non-commutative structure somehow simply performas a random walk, and this random walk is guided by the statistical picture encoded in it. (this is the entropic sense). Now the conjecture is that this determines hte action of every system in the universe!

I can't explain it all here, for several reasons, one of them is that it's still work in progress. But I guess I'm naive enoough to think the idea i simple enough to be conveyable, but maybe I'm wrong.

So the idea is that, IF this is right, the action of ANY system, IS understood in terms of of simply doimg random walks, but the KEY is that that the prior that determines this walk is encodd in each observer. This means that the action of say an electron, is simply a random walk - from te point of view of te electron! (ie the NAKED picture) but the renormalized picture, where a laboratory frame sees it, it's far from random.

So what I say is the randomness is relative/subjective.

I honestly see nothing of this as naive. I agree that it's probably formally naive of me to think I could work this out, but the idea is not naive. It's quite involved.

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.

As explain above, ENTROPY is not the primary starting point for me. But I still associate to verlinde because after all ENTROPY simply IS an alternative probability meausre of distributions. I work directly with the latter. But the thinking is similar.

About fundamental interactions, the idea is this: From the point of view of scientific INFERENCE, or even physical interactions, whatever the fundamental interactions ARE (in a realist picture) the question from the point of view of inference is still to INFER them! And this INFERENCE does render the establisehd interactions as equilibrium states of the random inferences. The learning part sits in the evolutionary survival and selection of the structurres encoding this.

also I am not assuming the regular holographic form; instead the holographic principle is in my view also an equilibrium condition - and I see it as the duality between how two observers encode an agreement. The "surfafce" can be thought of as the communication channels between them. It does not at deepest mean that they encode the SAME ifnoramton, it just means that the COMMUNICABLE information is thesame. The channels may strip some information out, but no party can find that out, by communicating further :)

/Fredrik
 
  • #27
Fra
3,619
369
So I rather postulate something like "rational expectation", "rational action" that follow from a reconstruction of a discrete version of probabilit theory, that is based on counting evidence

The idea is that the expectation follows simply from a rational assessment for counting information. This further suggest that the action/choice of action is RANDOMLY chosen with respect to this expectation. Ie. there is NO reason for a particular action, which results in a random walk.

The trick is then to SCALE this, and to see how a random walk looks like a non-random walk with respect to another observer. This relativiity of randomness is somply due to they not sharing the same prior. This is also why two observer can never encode the same information state.

Two observers doing so, would be indistinguishable also with respect to other observers because they act as if they encode the same iformation. (any difference is expected to the randomly distributed with respect toe hte other observer - thus she can't distinguish)

The construction of the actions of SM would in principle involve pictuering evolutionary selection among such interacting systems, it would alos mean there are not classical actions. Even the classical actions we know should have a statistical orign.

During this evoluion, of increasing complexity, an hierarchy of structure and interactions will emerge. Interactions between two systems are ultimatly rooted in "two systems doing random walks; but where they disagree with that's random. This makes this look like a negotiation process". Gravity in this picture I loosely think of as distance measure in between sytems and that ANY such negotiation process is always attractive regardless of the details of the inference. So it' predicts a generically attractive force that would somehow depden on the overall complexity of thte systesm. At some point GR or newtons laws must follow from this in the appropriate limit or else this idea is wrong. So there are lots of such consistency checks.

This is why gravity is probably one of the first interactions to emerge in this picture, it's just that this first form of proto-gravity splits off into encoding the other interactions as the complexity is scaled up.

The problem is not that these are random or incoherente ideas, the problem is to implement and work out all details. But having the vision certainly helps digging in the right direction.

/Fredrik
 
  • #28
CHIKO-2010
90
0
Dear Fredrik,

I have tried hard to understand what your are talking about in your posts but failed. frankly, your writings don't make sense to me.

In my posts entropy has very standard definition -- it is a quantity that characterizes statistically large number of microscopic particles. There is no sense to talk about entropy of a given particle. Therefore, if a force is due to the entropy change, i.e. due to the "collective effect" of microscopic particles/sates, rather than due to the exchange of force-career particles, such as photons, gravitons, etc, then in such a theory there is no room for photons, gravitons, etc...Empirically, we do not know whether gravitons exist or not, while we do know that photons exist. Therefore, at least electric forces cannot be entropic.

Moreover, there is a rather convincing experimental evidence that particles described by pure states (that is having 0 entropy) also gravitate. These are interference and free-fall experiments with neutrons. these experiments, in my opinion, clearly show that Verlinde's proposal is wrong.

However, it looks like you are talking about something different, which I am not able to understand. Good luck with your vision!
 
  • #29
Fra
3,619
369
However, it looks like you are talking about something different, which I am not able to understand. Good luck with your vision!
Yes Chiko, I'm talking about something different, so I supposed I am possibly naive in thinking that you would see what I mean. The proper explanation I supposed would have to wait until I have succeded the implementation. Verlindes specific proposal, is not the answer even to me. The only reason I defend it is because I think it's a step in the right direction. Verlinde assumes the holographic principle - I don't. That's one difference, but there are more.

One issue is what is meant with entropy. There are several specific entropy measures, von neumann entropy.
pure states (that is having 0 entropy)
You seems to speak of standard von neumann entropy here, and you assume already the whole QM framework - I am reconstructing all of this.

The missing information measured by von neumann entropy is in my view grossly underestimating the actual missing information. In the ordinary picture, alot of information is frozen in realist structure of the theory. These are relaxed and become alive in my view.

So your argument based on von neumann entropy does not at all invalidate my vision.

This is why I started to first say what "entropy" in hte general sense is. There are SEVERAL measures of entropy - is one of them more correct? Generically entropy is simply a measure of how probable a given probabiltiy distribution is, relative to the ergodic hypothesis and a prior. I work directly with the reconstructed probability.
In my posts entropy has very standard definition -- it is a quantity that characterizes statistically large number of microscopic particles. There is no sense to talk about entropy of a given particle. Therefore, if a force is due to the entropy change, i.e. due to the "collective effect" of microscopic particles/sates, rather than due to the exchange of force-career particles, such as photons, gravitons, etc, then in such a theory there is no room for photons, gravitons, etc...Empirically, we do not know whether gravitons exist or not, while we do know that photons exist. Therefore, at least electric forces cannot be entropic.
I see the confusion, sorry. As I tried to say, a common critique to ALL various entropic or maxent methods etc is that the notion of entropy is ambigous. Or more specifically the entropy measure itself is always relative or subjective. I am taking this more seriously and therefor I have to reject the simple entropic notion you refer to.

The neumann entropy is only objective to the extent that the measuremetn context (classical reality) is. And of course it is to an FAPP extent in many cases. But this is not good enough for a reconstruction. FAPP is not close enough. Ie. von neumann only measure the "quantum mechanical entropy" not what I call he FULL entropy (including what's frozen in the von neumann picture).
In my posts entropy has very standard definition -- it is a quantity that characterizes statistically large number of microscopic particles. There is no sense to talk about entropy of a given particle.
How do we define the particle? In normal QFT the definition of a particle is usually strongly connected to QFT and poincare symmetry of spacetime. These are completely invalid startign poitns in the view. Thus the notion of "particle" as we usually mean it, has no place in the starting points in my construction.

In my view, everything, even the particle notion (when used) is inferred from the interaction history, and the new "entropy" is defined relative to complexions in the histories; or the encoded histories. In this abstraction it becomes impossible for an interial particle to not have hidden information, because these complexions is what yields the sytems it's inertia.

Compare to a decision theoretic problem. The inertia of one player, is due to that it takes a certain AMOUNT of contradicting information to rationally CONVINCE her to revise the opinion. This is why when a massive and light system interacts, both will approach each other, but the massive system influences the light one to a larger extent than vice versa exactly due to this bully mechanism.

Gravity is universal becase every information processing system is subject to this kind of inertia. In this view inertial mechanism and gravity is the same mechanism. When two inertial systems communicate, the gravitatioanl interaction is there independent of hte details of the interaction.

So what I envision goes far beyond verlinde, new entropy and different understanding of holography. But it's still in the same direction. IF you want to reconstruct alot, then it's alot more work. Verlinde is more doing a limited arguement that I see as an appetizer at best. But for ME at least, the critique against verlinge applies to this specific assumptions that I think need to be relaxed anyway, just making the argument much stronger.

I guess we won't reach a conclusion here but, to dismiss all statistical origin of forces due to verlindes paper is I think unfair. To do this, several of this things that are critiqued WILL need to be reworked.

I've been focusing in this direction for some time and I am very confident that there is something really nice to be discovered here. This is why I find it's a pity if the general direction gets bad name due to some first steps. The risk is that people misjudge a bigger vision but some first incomplete suggestions.

This is in fact exactly why I have decided long time ago to NOT publish anything in detail until I have reached a certain level of development on my own. There is an obvious chance that people will misjudge it, no matter how much disclaimers is put that it's a first step. It may damage the idea more than promoting it, to publish something immmature. Because people will immediately jump on all the incomplete parts no matter if declared so.

This is why I prefer to give thumgs up on Verlindes paper! Not because it's perfect, but simply because he is onto something.

/Fredrik
 
  • #30
CHIKO-2010
90
0
Ok Fredrik, thanks for your efforts to explain your point of view. I won't go any further because:

1. this is not the theme of this thread;
2. I won't be able to understand this stuff;
3. you won't be able to explain it better, until you come up with something as particular as standard QM+relativity.

I only wish you success in your endeavor.

P.S. Verlinde's paper is not just imperfect, it is WRONG.
 
  • #31
Fra
3,619
369
P.S. Verlinde's paper is not just imperfect, it is WRONG.

From a certaint perspective possibly yes, but any learning process means you are wrong alot of times along the way. From the point of view of learning though, beeing wrong is similary to be imperfect. The different is if you suffice with saying that this does not work, or if you are able to see how the spirit is right but the details are wrong, and instead suggest how it can be improved :)

For me the biggest point of Verlindes paper is the spirit of intent that I think is good, not the details that one could argue is wrong. But what's wrong is I think not because he looks into the entropic reasoning, but because he doesn't take the spirit FAR enough. He is doing some semiclassical toying. It's expected that it's not quite satisfactory.

So I hail him for trying, not blame him for not beeing able to solve all problems at once.

/Fredrik
 
  • #32
czes
222
1
P.S. Verlinde's paper is not just imperfect, it is WRONG.

The articles cited by MTd2 :
The only comment it received was a brief half - paragraph of this paper, page 8, citation [25]:
http://arxiv.org/PS_cache/arxiv/pdf/...010.4729v2.pdf [Broken]
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.

suggests that Verlinde's idea is correct above the quantum level because the most fundamental is the conservation of the quantum information.

I agree with Fredrik that entropy is very important and it shows that gravity is not a fundamental force.
 
Last edited by a moderator:
  • #33
CHIKO-2010
90
0
[/QUOTE]suggests that Verlinde's idea is correct above the quantum level because the most fundamental is the conservation of the quantum information.

I agree with Fredrik that entropy is very important and it shows that gravity is not a fundamental force.[/QUOTE]


Dear Czes, I do not know how the Susskind paper 1101.6048 negates the criticism of 1009.5414. Do you? Or it just the authors name that makes you think that the paper must be right by default?

I wonder, how can you agree with Fredrik on the stuff (Verlinde gravity) that he does not believe himself?
 
Last edited:
  • #34
czes
222
1
For me the explanation is rather in the previous paper:
http://arxiv.org/PS_cache/arxiv/pdf/1010/1010.4729v2.pdf
With respect to the criticism (experiment with ultracold neutrons) , we argue that there is no reason to assume that the typical length scale of the experiment (l=~1 um, is the one associated with entropy change dx (dS=k dx/l(c)).
Indeed , assuming that space is an emerging feature from a coarse graining procedure, the question is: what is the graining scale?
It seems natural to assume that the former is such that it is much greater than Planck length and even the Compton length of the particle.
Probably the experiment establishes a "gravitational" drawing line between quantum and classical behaviour given the dependence of its energy spectrum on the mass of the testing particle.
This means that a particle can be regarded as quantum from the gravitational point of view only if its size is smaller than the spacing between the energy levels of the corresponding Gravitational Quantum Well.
 
  • #35
CHIKO-2010
90
0
For me the explanation is rather in the previous paper:
http://arxiv.org/PS_cache/arxiv/pdf/1010/1010.4729v2.pdf
With respect to the criticism (experiment with ultracold neutrons) , we argue that there is no reason to assume that the typical length scale of the experiment (l=~1 um, is the one associated with entropy change dx (dS=k dx/l(c)).
Indeed , assuming that space is an emerging feature from a coarse graining procedure, the question is: what is the graining scale?
It seems natural to assume that the former is such that it is much greater than Planck length and even the Compton length of the particle.
Probably the experiment establishes a "gravitational" drawing line between quantum and classical behaviour given the dependence of its energy spectrum on the mass of the testing particle.
This means that a particle can be regarded as quantum from the gravitational point of view only if its size is smaller than the spacing between the energy levels of the corresponding Gravitational Quantum Well.


This criticism is absolutely invalid. MTd2 was trying to come up with something similar in the previous discussion, see the thread Gravity is not entropic force?. I repeat again: The derivation of the entropic force by Verlinde does not depend on a particular value of dx -- the force itself is proportional to the gradient of the entropy dS/dx. Similarly, derivation in 1009.5414 does not depend on any assumption on dx in the equation for the entropy change. The only relevant point in 1009.5414 is the entropy change which is associated with the change in the position of neutron, NOt with some microscopic coarse graining length. Neither verlinde's paper nor 1009.5414 depend on the microscopic details of the theory. It is surprising you are not able to understand this simple, basic point.
 

Suggested for: Verlinde's gravity basics

  • Last Post
Replies
1
Views
2K
Replies
4
Views
2K
Replies
3
Views
4K
Replies
18
Views
7K
Replies
8
Views
3K
Replies
23
Views
8K
  • Last Post
3
Replies
82
Views
29K
Replies
2
Views
3K
Replies
6
Views
8K
  • Last Post
2
Replies
35
Views
16K
Top