Does the LIGO experiment shed any light on the idea that Gravity is an Entropic Force over a Quantum Field Force?
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$\begingroup$ Define what you mean? What is an entropic force? $\endgroup$– Bob BeeCommented Nov 11, 2016 at 1:22
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$\begingroup$ It is what Erik Verlinde is proposing, that it is analogous to a thermodynamic like event. So, no force particle but an equilibrium reached thru entropy. Hope that helps. $\endgroup$– Ed YableckiCommented Nov 11, 2016 at 1:34
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$\begingroup$ Was this prompted by Verlinde's new paper, "Emergent Gravity and the Dark Universe"? $\endgroup$– Peter MortensenCommented Nov 16, 2016 at 16:34
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1 Answer
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Entropic gravity has been around since Erik Verlinde around 2010, but it does not seem to have found any experimental backup since then. I don't see many papers on entropic gravity either nowadays.
Motl just about totally assassinated (or demolished) Verlinde's theory, and that is probably applicable to Jacobson's similar theory. See Motls's energetic demolishment of entropic gravity at http://motls.blogspot.com/2010/07/many-faces-of-emergence.html
Carroll had a recent paper in 2016 in arxiv that discusses holographic and entropic gravity (Jacobson's version, similar to Verlinde's but not identical), and argues that holographic gravity (using the holographic principle) can be made consistent with quantum field theory and supports various entanglement ideas, but that in entropic gravity it does not seem possible to formulate a consistent definition of entropy. See it at https://arxiv.org/abs/1601.07558.
That is fairly consistent with Motl's earlier blog article that one cannot define entropy in entropic gravity such that a locally Lorentz invariant treatment is possible. Motl argues that it also in fact it runs counter to observed experimental results of neutron double slit interferometers in gravitational fields, that entropic gravity would be inconsistent with the equivalence principle.
Motl argues that other quantum gravity theories like string theory and holographic gravity do not have those inconsistencies, Carroll argues similarly for holographic gravity in significant but not thoroughly mathematical detail.
I have not done a literature review to see all the latest, and a cursory search did not find much, and I've not heard any recent highlighting news for entropic gravity. Not sure how alive it is.
So, as far as LIGO is concerned, it has been found 100% consistent with Einsteins GR, the equivalence principle, and the GR calculations (they not only find the parameters for the gravitational waves, but also if there is any deviation from that predicted through GR computations, and the sigmas to which verified). See the GR tests from LIGO's first detection at
http://www.ligo.org/science/Publication-GW150914TestingGR/
LIGO will do more GR and in fact alternative gravity tests (but I've not seen anything on entropic gravity, maybe others have from LIGO), as it gets more sensitive, and other interferometer arrays get combined into a network. eLISA space borne interferometers in the next decade would be even more sensitive. They expect to be able to probe the extent to which for instance black holes do or do not have 'hair' (I.e., any other conserved properties besides mass, angular momentum and charge), as well as some of the parameters during the dynamic merger phases when the horizons are deformed, and other tests of gravity and GR.
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$\begingroup$ Sure Ed Yablecki. It's good question and there continue to be proposed alternatives, mainly to try to explain the dark energy and try to make it more quantum friendly, but none that don't reduce to GR in the right limit have had any evidence for them. So far. You never know. The hottest topic has been the holographic correspondence, for a quantum correspondence, but still too many unknowns on it $\endgroup$– Bob BeeCommented Nov 13, 2016 at 1:27
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$\begingroup$ Shouldn't you take Verlinde's paper "Emergent Gravity and the Dark Universe" into account, published about 3 days prior to this answer? $\endgroup$ Commented Nov 16, 2016 at 16:28
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$\begingroup$ @peter, feel free to do so in formulating an answer. I've not evaluated it yet $\endgroup$– Bob BeeCommented Nov 17, 2016 at 18:57