Saturday, May 28, 2011

Entropic Gravity


Eric Verlinde


Verlinde's statistical description of gravity as an entropic force leads to the correct inverse square distance law of attraction between classical bodies.

Entropic gravity is a hypothesis in modern physics that describes gravity as an entropic force; not a fundamental interaction mediated by a particle, but a probabilistic consequence of physical systems' tendency to increase their entropy.

Origin

The probabilistic description of gravity has a history that goes back at least to Richard Feynman in the early 1960's,[1] and to research on black hole thermodynamics by Bekenstein and Hawking in the mid-1970s. These studies suggest a deep connection between gravity and thermodynamics, which describes the behavior of heat and gases. In 1995, Jacobson demonstrated that the Einstein equations describing relativistic gravitation can be derived by combining general thermodynamic considerations with the equivalence principle.[2] Subsequently, other physicists began to explore links between gravity and entropy.[3][4]

Erik Verlinde's theory

In 2009, Erik Verlinde disclosed a conceptual theory that describes gravity as an entropic force.[5] On January 6, 2010 he published a preprint of a 29 page paper titled On the Origin of Gravity and the Laws of Newton.[6] (It was published in April 2011).[7] Reversing the logic of over 300 years, it argued that gravity is a consequence of the laws of thermodynamics. This theory combines the thermodynamic approach to gravity with Gerardus 't Hooft's holographic principle. If proven correct, this implies gravity is not a fundamental interaction, but anemergent phenomenon which arises from the statistical behavior of microscopic degrees of freedom encoded on a holographic screen. The paper drew a variety of responses from the scientific community. Andrew Strominger, a string theorist at Harvard said “Some people have said it can’t be right, others that it’s right and we already knew it — that it’s right and profound, right and trivial."[8]
Verlinde's article also attracted a large amount of media exposure,[9][10] and led to immediate follow-up work in cosmology,[11][12] the dark energy hypothesis,[13] cosmological acceleration,[14][15] cosmological inflation,[16] and loop quantum gravity.[17] Also, a specific microscopic model has been proposed that indeed leads to entropic gravity emerging at large scales.[18]


Critique

Verlinde’s theory is criticized [19] on the basis that it fails to reproduce gravitational bound states of neutron observed in the experiments with ultracold neutrons[20]


See also


References

  1. ^ R.P. Feynman, The Character of Physical Law (Messenger Lectures, 1964): Lecture 2 on The Relation of Mathematics to Physics; Feynman's attempt at a statistical description of gravity starts 7 minutes into this video clip
  2. ^ Jacobson, Theodore (4 April 1995). "Thermodynamics of Spacetime: The Einstein Equation of State". Phys.Rev.Lett.75:1260-1263,1995 75 (7): 1260–1263. arXiv:gr-qc/9504004.Bibcode 1995PhRvL..75.1260Jdoi:10.1103/PhysRevLett.75.1260.
  3. ^ Padmanabhan, Thanu (26 November 2009). "Thermodynamical Aspects of Gravity: New insights". Rep. Prog. Phys. 73 (2010)01 73 (4): 6901. arXiv:0911.5004Bibcode2010RPPh...73d6901Pdoi:10.1088/0034-4885/73/4/046901.
  4. ^ Mok, H.M. (13 August 2004). "Further Explanation to the Cosmological Constant Problem by Discrete Space-time Through Modified Holographic Principle".arXiv:physics/0408060 [physics.gen-ph].
  5. ^ van Calmthout, Martijn (12 December 2009). "Is Einstein een beetje achterhaald?" (in Dutch). de Volkskrant. Retrieved 6 September 2010.
  6. ^ Verlinde, Eric (6 January 2010). "Title: On the Origin of Gravity and the Laws of Newton". arXiv:1001.0785 [hep-th].
  7. ^ E.P. Verlinde. "On the Origin of Gravity and the Laws of Newton". JHEP 04, 29 (2011)doi:10.1007/JHEP04(2011)029.
  8. ^ Overbye, Dennis (July 12, 2010). "A Scientist Takes On Gravity"The New York Times. Retrieved 6 September 2010.
  9. ^ The entropy force: a new direction for gravityNew Scientist, 20 January 2010, issue 2744
  10. ^ Gravity is an entropic form of holographic informationWired Magazine, 20 January 2010
  11. ^ Fu-Wen Shu; Yungui Gong (2010). "Equipartition of energy and the first law of thermodynamics at the apparent horizon". arXiv:1001.3237 [gr-qc].
  12. ^ Rong-Gen Cai; Li-Ming Cao; Nobuyoshi Ohta (2010). "Friedmann Equations from Entropic Force". Phys. Rev. D 8101(R) (2010) 81 (6). arXiv:1001.3470Bibcode2010PhRvD..81f1501Cdoi:10.1103/PhysRevD.81.061501.
  13. ^ It from Bit: How to get rid of dark energy, Johannes Koelman, 2010
  14. ^ Easson; Frampton; Smoot (2010). "Entropic Accelerating Universe". Phys.Lett.B696:273-277,2011 696 (3): 273–277. arXiv:1002.4278Bibcode 2011PhLB..696..273E.doi:10.1016/j.physletb.2010.12.025.
  15. ^ Yi-Fu Cai; Jie Liu; Hong Li (2010). "Entropic cosmology: a unified model of inflation and late-time acceleration". Phys.Lett.B 690:213-219,2010 690 (3): 213–219. arXiv:1003.4526.Bibcode 2010PhLB..690..213Cdoi:10.1016/j.physletb.2010.05.033.
  16. ^ Yi Wang (2010). "Towards a Holographic Description of Inflation and Generation of Fluctuations from Thermodynamics". arXiv:1001.4786 [hep-th].
  17. ^ Lee Smolin (2010). "Newtonian gravity in loop quantum gravity". arXiv:1001.3668 [gr-qc].
  18. ^ Jarmo Mäkelä (2010). "Notes Concerning "On the Origin of Gravity and the Laws of Newton" by E. Verlinde (arXiv:1001.0785)". arXiv:1001.3808 [gr-qc].
  19. ^ Kobakhidze, Archil (15 January 2011). "Gravity is not an entropic force". Phys. Rev. D83: 021502,2011 83 (2): 021502(3 pages). arXiv:[hep-th arXiv:1009.5414 [hep-th]]. Bibcode2011PhRvD..83b1502Kdoi:10.1103/PhysRevD.83.021502.
  20. ^ Nesvizhevsky, V.V., et al. (17 January 2002). "Quantum states of neutrons in the Earth's gravitational field". Nature 415: 297-299. Bibcode 2002Natur.415..297N.doi:10.1038/415297a.

]Further reading

9 comments:

Neil Bates said...

Another in a line of clever "equivalent ways to look at ..." like advanced+retarded potentials, least action, all-paths integrals etc. But in that case, why pretend that the other "ways" are not valid or are supplanted rather than "paralleled"? Also, his concept does not and cannot (?) explain the value of "G." Yes, I know that G has units and is not like alpha, but we can still imagine it different but other constants the same.

Ulla said...

This builds on assumptions of a 'real' Universe. How can it emerge? And note there is no G in the fine structure constant, only hbar etc.

I think too early to give him the Nobel. It could be devastating for the future. He express himself uncertainty about this?

Neil Bates said...

Ulla: right, I was saying that FSC is dimensionless (constructed from e, h and c) whereas G has dimensions. Some people think that only changes in DCs is noticeable, but clearly that isn't so since it's easy to imagine G changing (ie, not like "everything bigger", note e.g. different ratios grav. to EM forces etc.) I skimmed your FQXi article (what a disappointment, the low ratings for almost all articles) and maybe you can summarize what you mean by "realness,"

Phil Warnell said...

Hi Steven,

I would have to agree with Einstein in respect to any theory when it cites statistics as thinking it holding as an explanation that serves to have anything found as understood. That being statistical explanations are what is used to predict actions and outcomes in the absence of a complete explanation. I find this just an extension of the ‘shut and calculate’ philosophy in regards to physics, to have it being ‘shut up, stop thinking and calculate’.

“We have become Antipodean in our scientific expectations. You believe in the God that plays dice, and I in complete law and order in a world which objectively exists, and which I, in a wildly speculative way, am trying to capture. I firmly believe, but I hope that someone will discover, a more realistic way, or rather a more tangible basis than it has been my lot to find. Even the great initial success of quantum theory does not make me believe in the fundamental dice-game, although I am well aware that our younger colleagues interpret this as a consequence of senility.No doubt the day will come when we will see whose instinctive attitude was the correct one.”

-Albert Einstein, from a letter to Max Born, September 7, 1944, [Born-Einstein Letters]

Best,

Phil

Steven Colyer said...

I'm an Engineer, so "Shut Up and Calculate' is my mantra. NO professor would here a single complaint from me if he gave me something to calculate. Loved homework. Loved it loved it. That's how you bloody learn!

I hated tests though. Wish they would do away with the whole bloody lot of them, Just double the homework and have the professors collect them randomly. Less work for the professors, less time wasted by their great minds having to play "nanny" during tests and scoping out the suspected crib notes cheaters.

Phil Warnell said...

Hi Steven,

I didn't mean to suggest calculation doesn’t have its role, as for instance knowing the square of the hypotenuse being equal to the sum of the square of the other two sides, has little value without being able to calculate a square root and/or treat the elements as to know how to manipulate an equation. However all of this including the formulae for many is all that they know, simply having things confined to memorization; corresponding to being route learning lending no explanation as to why this is true. This can only be found in the conceptualisation of the things, or in other words through the proof of it being true; utilizing a combination of imagination and logic.

Moreover, in the course of my work I am exposed to as to communicate and complete projects with engineers (all of which are younger than me) and regrettably I have to report all as mostly limited in their problem solving and invention ability to the confines of those I described as route learners. I have also discovered when questioned on the foundations of what they claim to understand there is very little of this to that could be considered as being such. Now I’m not suggesting you are such an engineer, as in fact I would bet rather you are not. However I can testify from personal experience most I have observed are and thus would argue ‘shut up and calculate’ simply isn’t enough; especially when new situations arise and\or having a thorough analysis is required.

So the bottom line for me is when it comes to statistical explanations, although they allow accurate calculation within limits they don’t explain why any better than they do the same for a flip of a coin or the roll of a dice in relation to the actions and corresponding results of either.

“Information is not knowledge.”

-Albert Einstein

“Information? Whose information? Information about what?”

-J.S. Bell


Best,

Phil

Plato said...

Hi Steve,

What's interesting about engineers having worked along side of them off and on over the years, is the need for them to be specific about their calculations. I have found sometimes lacking on and about field application.

There is something they missed in their calculations, hence the work not coming out as it should, or just not applicable to the project at hand.

A lot of money(hundreds of thousands) to find it was a bust.

But onto your subject.

“Dr. Verlinde is not an obvious candidate to go off the deep end. He and his brother Herman, a Princeton professor, are celebrated twins known more for their mastery of the mathematics of hard-core string theory than for philosophic flights. A Scientist Takes On Gravity

Makes for interesting conversation.:)

Best,

Plato said...

Newton's inverse-square (1/r2) law is a cornerstone of General Relativity. However, this law has been challenged by many modern theories of gravity and particle physics. The supergravity and unified field theories often run into a new short-range force, with an accompanying new particle, which should appear as a violation of the 1/r2 law. More recently, a possible violation of the 1/r2 law in the range below 1 mm was suggested by string theories with extra dimensions.Newton's inverse-square (1/r2) law

Plato said...

Also Gravity Concepts-a useful site for many things.

Best,