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

• Entropic elasticity of an ideal chain
• Entropic force
• Gravitation
• Induced gravity

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..75.1260J. doi: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:0911.5004. Bibcode2010RPPh...73d6901P. doi: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 gravity, New Scientist, 20 January 2010, issue 2744
10. ^ Gravity is an entropic form of holographic information, Wired 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:1001.3470. Bibcode2010PhRvD..81f1501C. doi: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:1002.4278. Bibcode 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..213C. doi: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..83b1502K. doi: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

• It from bit - Entropic gravity for pedestrians, J. Koelman
• Gravity: the inside story, T Padmanabhan