Is Entropic Gravity the Future of Physics?

[marcus]

http://arxiv.org/PS_cache/arxiv/pdf/1003/1003.2312v3.pdf

Statistical Origin of Gravity

Rabin Banerjee, Bibhas Ranjan Majhi†
S. N. Bose National Centre for Basic Sciences,
JD Block, Sector III, Salt Lake, Kolkata-700098, India

Abstract

Starting from the definition of entropy used in statistical mechanics we show that it is
proportional to the gravity action. For a stationary black hole this entropy is expressed as S = E/2T , where T is the Hawking temperature and E is shown to be the Komar energy. This relation is also compatible with the generalised Smarr formula for mass.

For more information about the Banerjee Majhi paper see http://arxiv.org/abs/1003.2312
The abstract page indicates that it will be published in Physical Revlew D.
Even though it first appeared as recently as March 2010, the paper already has 17 cites.

Here is a brief quote from the introduction, just to serve as a sample:

"There are numerous evidences [1, 2, 3] which show that gravity and thermodynamics are closely connected to each other. Recently, there has been a growing consensus [4, 5, 6] that gravity need not be interpreted as a fundamental force, rather it is an emergent phenomenon just like thermodynamics and hydrodynamics.

The fundamental role of gravity is replaced by thermodynamical interpretations leading to similar or equivalent results. Nevertheless, understanding the entropic or thermodynamic origin of gravity is far from complete..."

I see that MTd2 spotted the Banerjee Majhi paper when it came out and added it to our bibliography of non-string QG links.
https://www.physicsforums.com/showthread.php?p=2619817#post2619817
The abstract is in post #1124 around page 71 of the biblio thread. I am glad that one of us saw it and included the link!

 

[catilina]

If gravity depends on entropy, and entropy depends on temperature, gravity would depend on temperature, isn't it?

http://www.enginsci.cn/ch/reader/create_pdf.aspx?file_no=20091215001&flag=1&journal_id=chinaes

 

[Fra]

Recently, there has been a growing consensus [4, 5, 6] that gravity need not be interpreted as a fundamental force, rather it is an emergent phenomenon just like thermodynamics and hydrodynamics.

I just want to note that a perfectly plausible possible future for the entropic business is also in connection to Smolin/Ungers idea of evolving law in general - ie. not JUST for gravity. Rather all laws as emergent.

This idea Unger basis on analogy with evolution of social laws are IMHO a much deeper vision thatn "just" the statistical emergence (from fundamental degrees of freedom) it ALSO contains the concept of negotiation and evolution of the fundamental degrees.

understanding the entropic or thermodynamic origin of gravity is far from complete..."

I think that what the future understanding of this, has to be MORE than just the simpler form of statistical emergence based on a timeless state space.

I'm personally convinced that this idea, in combination with evolution of statespaces is viable for the future.

In this view I think essentally all forces as of entropic, and that even strong weak and EM are branches of the same process. But I think to see that, we need to look beyond statistical emergence in the sense of simple entropic flows in fixed state space, I think one needs to ackwowledge that entropy and state spaces are observer dependent and that there exists no objective measures of these things. Fundamental degrees of freedom needs to also be subject to distinguishability and observability criteria, in an intrinsic measurement theory.

In ST - I think a possible hope exists if strings, including their background are replaced by an evolving picture. But there seems to lack such ideas so far. As I see it, the string, or a system of strings is to be seen as "the observer" interaction with other strings.

In LQG - I would like to see a more inference abstraction of their spin network, that does not harcode any dimenstionality, and that picutre generically interaction networks without prior reference to notions such as geometry or manidolfs or anything like that. As I see it, the spin networks or spin foams or a system theorof could represent the observers state, and this system itneracting with other spin networks...

It doesn't seem impossible either that there is a possible convergence there in the remote future. Even if all roads lead to Rome there should be better starting points that any of those as it's clear that the original founding principels of ST and LQG seem to me to be unsatisfactory.

/Fredrik

 

[oldman]

...(I, Fra) am a advocate of a view that includes kind of "entropic forces" (as another expression of rational action which is the idea that the action of any systems basically follows "random" motion in a evolving state space) ... /Fredrik

Pardon me for butting in on such an interesting thread, populated by folk who have views much more informed than mine, but your mention of "an evolving state space" is new to me. Is a 'state space' not a cousin to Hilbert space and to the old classical phase space?

If so, such spaces seem always to be taken as a fixed backdrop against which the system being considered evolves as the point? vector? that represents the system wanders about ergodically.

But it seems to me that there are situations where the abstract space itself (or at least the rather arbitrarily drawn subdivisions in it, or boxes (as Penrose calls them) which delineate macroscopically distinguishable systems) also evolves. I tried to ask a question about this in a recent thread in the Cosmology forum (Do changes of spacetime geometry affect entropy?), but perhaps that was the wrong place to ask it. Maybe you can enlighten me, here or there, Fredrik.

 

[Fra]

Pardon me for butting in on such an interesting thread, populated by folk who have views much more informed than mine

Then I should also pardon myself. There are a lot of knowledable people here but as I see it they each represent their own perspective. These are also open question so I would assume that as long as the discussion remains intellecutally sound, the more "butting in" the better discussion.

Is a 'state space' not a cousin to Hilbert space and to the old classical phase space?

If so, such spaces seem always to be taken as a fixed backdrop against which the system being considered evolves as the point? vector? that represents the system wanders about ergodically.

Yes, that's right. This is the *standard scheme*, and the historical ones of how physics has been abstracted.

But this standard scheme (which Smolin labeled the "Newtonian scheme" in his some of his recorded perimeter-talke on evolution of law; not to be mistaken with Newtons mechanics) is the picture that is challanged by for example the smolin/Unger reasoning. It is also a picture that I personally challange.

This standard picture, of timeless laws, initial conditions and timeless state spaces, is a form in which all known physics can be cast in. Classical mechanics, stat mech, qm, gr etc.

But it seems to me that there are situations where the abstract space itself (or at least the rather arbitrarily drawn subdivisions in it, or boxes (as Penrose calls them) which delineate macroscopically distinguishable systems) also evolves.

I don't know what example you have in mind but I agree with your general statement.

I tried to ask a question about this in a recent thread in the Cosmology forum (Do changes of spacetime geometry affect entropy?), but perhaps that was the wrong place to ask it. Maybe you can enlighten me, here or there, Fredrik.

I'll look at that thread later and see what the context is and if I can relate to it.

There are several arguments and ways to see why the notion of timeless law and timeless fixed state spaces are inadequate to describe certain situations and that they are even to a certain extent "unscientific" I won't repeat all arguments here but Smolin and Unger has presented some of them, they come from biology, social theory, cellular automata and other things.

One problem with the "entropic methods" in the context of the standard scheme, is the choice of the "right" entropy measure, or the right microstructure. Because the predictions or inferences made from this, depends on this CHOICE. If you don't take this seriously, the entropic reasoning still becomes "ad hoc". This problem is something that becomes very different if you instead acknowledge that there is no such universal measure, no intial value problem - instead the problem becomes how, and why, this evolution works and to explain the emergence of the de facto effective objective structure that we are familiary with from our human classical perspecitve.

/Fredrik

 

[friend]

...,instead the problem becomes how, and why, this evolution works and to explain the emergence of the de facto effective objective structure that we are familiary with from our human classical perspecitve.

/Fredrik

I'm wondering if the idea of "evolving laws" can be described alternatively as changes in symmetry as the universe expands. It might be that there are different symmetries at work in an early, tightly curved universe that break down into more recognizable symmetries as the universe becomes more flat. This would require symmetry breaking, right? This would require a change in the physical laws, right?

 

[humanino]

That abstract and paper is a good example of advertisement in theoretical physics. Its basically the standard CDT story to the T (albeit written well, its one of the better review papers for CDT on the market).

The authors pay lipservice to just about every other approach in the field, and only write 2 handwavey sentences about Verlinde's ideas (which admittedly is the very definition of handwaving in theoretical physics).

Its designed as a 'cite me' paper, most likely to raise some needed funding for better computers or somesuch.

I agree with your comments. I think it was worth (for people at my level) both pointing to the paper, as well as making your comments. I am glad you provided the comments, as I would not have considered myself qualified to formulate them.

 

[apeiron]

I'm wondering if the idea of "evolving laws" can be described alternatively as changes in symmetry as the universe expands. It might be that there are different symmetries at work in an early, tightly curved universe that break down into more recognizable symmetries as the universe becomes more flat. This would require symmetry breaking, right? This would require a change in the physical laws, right?

Isn't this standard thinking? That cooling results in a series of phase transitions that causes symmetries to crystalise out.

But rather than tightly curved, which implies closed globally hyperspheric curvature, I would associate the early hot state with local open hyperbolic curvature. A spacetime roil which is not flat but going off in many directions. A fat spacetime, so to speak. Room for multiple symmetries to be expressed still (in fleeting manner). But with cooling, the correlation length shortens. Fluctuations in "other" directions die away quickly. There is a phase transition so that generally spacetime is thin and flat (a crystalline structure) and trapped pockets of gauge symmetry (trapped quasi-particles).

So early on, all symmetries can be globally expressed. Hot spacetime is a mess of them. There can be fluctuations in any particular symmetry over all available scales - a critical state.

Then later, with cooling and thinning, the higher symmetries are globally suppressed. They can only exist as trapped hot pockets. The laws of physics would evolve with each change of state. Though really you still want a single description of the whole process.

 

[Fra]

I'm wondering if the idea of "evolving laws" can be described alternatively as changes in symmetry as the universe expands. It might be that there are different symmetries at work in an early, tightly curved universe that break down into more recognizable symmetries as the universe becomes more flat. This would require symmetry breaking, right? This would require a change in the physical laws, right?

The notion of Symmetry is indeed closely related to the notion of physical law. However IMO, the questioning of a deeper understandin of physical law, also then implies the quest for a deeper understanding of symmetry.

The common way of thinking, to picture - in a given fixed state space - a perfect symmetry in the sense that the laws of physics are invariant with respect to that, and that this symmetry is broken down in phase transitions as the energy scale changes, to produce a set of smaller symmetries, is still tied to the "old scheme" that I think is inadequate.

Just to explain how I see it: If we like to instead use the symmetry language, evolving law, means evolving symmetries, and the radical view I advocate and which I beleivce is in line with Ungers vision is not just a simple "breaking of a perfect symmetry". The reason is that the notion of symmetry is a bit complex too, becuase if you require that "knowing the symmetries" means having information about something, one must ask how the process looks like whereby this symmetry is a result of an inference. This thing is typically ignored in the standard scheme, if one tries to explain broken symmetries from a perfect fixed master symmetry.

To establish a symmetry, ie. to establish that some action is invariant with respect to certain transformations or complexions, one first need to establish the distinguishability of these complexions. And this is actuqally qa bit paradoxal, because if you have a strict invariance, then how is it possible to make an inference about this invariance? Something with the inference is wrong here. The conclusion seems to be that symmetries by nature are always unstable and evolving, and that a symmetry needs to be challanged in order to make sense.

To take an example, consider a blind man tell you that "I am indifferent to wether your clothes are red or blue". At first that may seem sensible, but the problem is that how can a blind man, in the first place, acquire the NOTION of COLOURS? This is not consistent.

It would be different is this guy had a history, where he used to see, and thus has a prior notion of something, that he by now have concluded is redundant (a symmetry).

Edit: instead the proper behaviour would isntead be that a blind man IS invariant with respect to your colours, BUT he would never launch such a statement! Rather if you mention the word red or blue, he just would understand you.

(Of course I'm simplifying here, but I think the point is illustrated; that the notion of INFERRING an INVARIANC is subtle)

This analysis of how an observer inferes, and relates to a symmetry, really connects the set of possible symmetries to the microstructure and makeup of the observer itself. Ie. symmetries are necessarily also observer dependent, in the sense that I think we should only talk about _inferrable_ symmetries.

In the standard framework, we talk about symmetries as existing in mathematical worlds, that are not subject to scientific inference process. To me this is a serious flaw.

I agree that evolving law, can similary be phrased in terms of evolving symmetries. But just like entropy observer dependent, so are laws and so are symmetries. And I mean observer dependent in a more general sense that JUST energy scale dependent. Energy scale does set constraints or limits, of the complexity of law - this is why inferrable laws are destined to unification (all beeing one indisitinguishable interaction) as the energy scale increases (which from the inside view means the opposite! the compleixty of inside observers goes to zero - this is why encoding complex diverse law just isn't possible from an information theoretic inference persepctive)

/Fredrik

 

[John86]

A new Mathematical framework (less rigid) is than needed, maybe something transcending nowadays mathematics ?..

 

[Fra]

A new Mathematical framework (less rigid) is than needed, maybe something transcending nowadays mathematics ?..

Yes, exactly.

That's not to say we don't need mathematics. It just means that we can't expect to view physics as a timeless axiomatic system. It would rather have to be an evolving axiomatic systems, where axioms can be created and destroyed.

Essentially some intelligent learning framework.

/Fredrik

 

[friend]

A new Mathematical framework (less rigid) is than needed, maybe something transcending nowadays mathematics ?..

If mathematics can be derived from logic, then you'd have to transcend reason (logic) in order to transcend mathematics. I assume that whatever ultimate laws of physics are, they are reasonable, consistent, and logical. It remains to see how to describe the logical laws of physics with the use of mathematics.

 

[Fra]

If mathematics can be derived from logic, then you'd have to transcend reason (logic) in order to transcend mathematics. I assume that whatever ultimate laws of physics are, they are reasonable, consistent, and logical. It remains to see how to describe the logical laws of physics with the use of mathematics.

As ET Jaynes phrased it, probability theory is an extension of logic, and a basis for rational reasoning.

Also two systems can reason perfectly rational, from their perspective, yet enter into a mutual inconsistency. This inconsistency we can classify as an interaction between the two. But the classification of the interactions is also observer dependent, as the inconsistency will be described differently depending on the context. There is no perfect external view.

The main problem as I see it, is that "logical inferences" or "rational inferences" are in fact not unique or objective. There are different possible mathematical models. WE need to consider the physical process wherby the axioms are CHOSEN, only then may we see that they aren't chosen randomly from an infinite set of possible axioms, they have evolved as constructively emerging self-preserving structures. (analog to biology)

This is why I don't think it's viable to think of mathematical descriptions as timeless or objective, because there seems to be no rational basis for that expectation. The remaining option seems to be to look for an evolving system of interacting "logical systems", where each logical system represents an observer or subsystem of the universe.

/Fredrik

 

[John86]

Does evolution by your means always incorporates growing complexity in the sense that at some moment there must be some starting point, where the evolution or cutoff moment starts.

Or is it tree like where branches seperating

 

[Fra]

Does evolution by your means always incorporates growing complexity in the sense that at some moment there must be some starting point, where the evolution or cutoff moment starts.

If we picture observers or arbitrary complexity, then the evolution I envision has to include mechanism for increasing, as well as decreasing complexity. I picture this process closely related to generation of mass.

In the gaming analogies, this can be assocaited to how one player, by beeing more clever and sometimes also having luck, can conquer control over it's environment and "grow" in it's quest for self-preservation.

It's this mechanis, where two systems try to conquer each othre that is responsible for the attractive force of gravit in my view. Their constant communication makes the information distance between them shrink, and thus the distance in between them shrinks.

But evolution process isn't just the complexity. When the complexity has reached a steady state for a given observer, there is still an ongoing evolution which can be interpreted as a redisposition and remapping of available resources.

So, no it does not always increase complexity, as in an monotonous increasing function. That would make no sense. The point is that complexity growth or decreasing are very SLOW processes as compared to the redisposition processes. this is why on a short time scale, these "gravitational like" effects can be accounted for my constants.

Edit: In my picture the PART of evolution having to do with scaling complexity, is the thing that I associated closests to "gravity". The part of evolution that is superimposed ontop on, or taking place within the constant complexity domain, are what I associate to the other forces (non-gravitational ones). Still I'm quite convinced that even the understanding of the forces, in particular their unification, requires an analysis of also the complexity scaling processes. Most certainly, something closely related to, or even exactly equivalent to Quantum mechanics as we know it, is the result when complexity is frozen. But this is clearly a special case, and interesting insight await if we understand the general case.

/Fredrik

 

[John86]

Thank you, very illuminating, i'ts what i wanted to hear.

I hope these idea will be worked out in the near future, it will have impact how we think of nature.

 

[dantsmith]

It appears to me that Verlinde is headed in the direction of idealism, not to mention the Strong version of the Anthropic principle.

[BTW, is there likely to be a more active discussion of Erik, than on this forum?]

I'm a bit surprised that this discussion already seems to have died down. I only learned of his arXiv paper a few days ago, after reading the recent NYT review.

I can easily understand why the physics community is taking a wary approach to his radical ideas. It goes strongly against the Pythagorean/Platonic dispositions of most of my former colleagues, that being one reason why I left the field, in pursuit of a stronger take on anthropics. No until Erik, have I seen such support from physics.

I am more than a bit concerned that if I make too much of Erik's idea(lism) that it may only serve to foment more resistance, but be that as it may.

To use another dirty-word, might he not also be seen as a post-modern Newton?

Do we not recall the http://en.wikipedia.org/wiki/Sokal_affair" ? It would seem that Verlinde constitutes a partial reprise of that affair, even down to the dialectic, but this time the dialectic is more after the mode of Hegel than of Marx.




(cont.)

 

[MTd2]

Idealism in Erik's gravity? I don't get it.

 

[marcus]

It appears to me that Verlinde is headed in the direction of idealism, not to mention the Strong version of the Anthropic principle.

[BTW, is there likely to be a more active discussion of Erik, than on this forum?]

I'm a bit surprised that this discussion already seems to have died down. I only learned of his arXiv paper a few days ago, after reading the recent NYT review.

Dan, a lot of people when they use words like Strong Anthropic, they are heading into a relgious discussion and they have in mind things like God and Intelligent Design.

I don't think there is much new in what Verlinde has offered so far. More hype than substance. Much of what he is making noise about was covered already by Jacobson (1995) and Padmanabhan.
I don't think there is any "Strong Anthropery" in what Verlinde is publicizing. That would be very much your own spin.

I can easily understand why the physics community is taking a wary approach to his very radical ideas. It goes very strongly against the Pythagorean/Platonic dispositions of most of my former colleagues, that being one reason why I left the field, in pursuit of a stronger take on anthropics. Not until Erik, have I seen such support from physics.

I am more than a bit concerned that if I make too much of Erik's idea(lism) that I may only, be fomenting more resistance, but be that as it may.
(cont.)

Sounds like delusion, Dan. Erik Verlinde is not "supporting" your "pursuit of a stronger take on anthropics". He is just stirring up hype for a not-too-radical career leap.

AFAICS there is no need for you to be concerned about "fomenting more resistance". I could be wrong but I doubt anything you could say would change physicists' views of Verlinde's initiative.

Don't get me wrong. Except in the media and popularization department Verlinde is a minor player, he represents the overcrowding in the current string doldrums, and the need felt by stranded theorists to find something new to be enthusiastic about. They are looking for bridges out of main core string. But that said, the thermodynamic study of gravity is, I think, highly important. Specifically, the thermodynamics of spacetime geometry.
This is what people like Jacobson and Padmanabhan have written seminal papers about. I expect research in this to grow and get quite interesting over the next 5 years or so.

 

[dantsmith]

Marcus,

Thank you for your prompt and thoughtful response.

Yes, it is true that I left the groves of physics for the loftier climes of metaphysics, and have only been lurking down here, since.

Now, I do not wish to make a nuisance of myself, in a very academically inclined venue, BUT, I might be able to make a few useful, interesting, and even amusing, observations, that are triggered, in part, by poor Erik's attempt to achieve a semblance of notoriety and/or job security, although these do seem like conflicting motives.

But first, I have been scrounging in the philosophy and religion forums looking for a place to discuss alternative cosmologies, with very little success. I have been active mainly at something called Open Minds forum for the last several years, to which I will return, after testing other waters.
---------------------

Upon further inspection, perhaps I should head over to the philosophy section and start a thread there...

Again, Marcus, thank you for your polite and thoughtful reception to a newbie!

 

[marcus]

...
Upon further inspection, perhaps I should head over to the philosophy section and start a thread there...

That's not a bad idea. I see you now have done so!
https://www.physicsforums.com/showthread.php?t=417688
Good luck with it!

 

[jaquecusto]

I wonder if it is possible to conceive a cosmic machine, capable of running without gravity, using only tested physical concepts. For example, a planet is attracted by a star by the Bernoulli effect.

 

[John86]

I found this update by Johannes Koelman today.
Erik Verlinde is working o a new paper about Entropic Gravity !.


http://www.science20.com/hammock_physicist/blog/entropic_gravity_snatches_spinoza_prize-79902