What I understand is that you’re asking “is there a good quantum-scale description of emergent gravity?”

Mudassir Ali
Feb 18, 2020 05:38 AM 0 Answers
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Mudassir Ali
- Feb 18, 2020 05:38 AM

At least a couple of fascinating papers in the spirit of this idea have appeared recently in the literature. One highly ambitious paper [1611.02269] Emergent Gravity and the Dark Universe by Erik Verlinde posits that a fundamentally quantum mechanical model in which spacetime is emergent could potentially provide a radical alternative explanation for dark matter as a consequence of long-range entanglement that violates gravity according to Einstein on scales larger than the Hubble scale. As far as theoretical physics papers go this is highly esoteric and I think very few of us even grasp the salient ideas of this proposal. Needless to say it’s a thrilling idea!

Secondly there’s this recent paper Recovering Geometry from Bulk Entanglement by Sean Carroll that describes an explicit quantum mechanical model in which spacetime is emergent. Here, spatial geometry arises from entanglement between a discrete set of quantum mechanical subsystems. How such a crazy-sounding idea can be well motivated boils down to various hints we’ve ascertained mostly in relation to our attempts to resolve the black hole information paradoxes. One such hint comes from Leonard Susskind’s ambitious ER=EPR proposal in which he claims that quantum mechanical entanglement is the same thing as spatial connectivity. This is delightfully encapsulated in the name that pertains to the idea that an EPR pair of entangled quantum particles is the same thing as an ER bridge (wormhole) connecting the two particles. In Sean Carroll’s paper, this idea is effectively pushed to its logical conclusion, taken at face value. A tantalising aspect of this model is that if you insert mass/energy in his model, this has the effect of altering the entanglement structure of the state; since spatial geometry emerges from the entanglement structure then we see that spatial geometry changes in response to the presence of mass/energy in a way that’s qualitatively similar to gravity according to General Relativity!

In terms of a definitive model describing our universe along with it’s zoo of matter and forces we’re a long way off, but the idea of emergent gravity is very much alive and fascinating ideas such Erik Verlinde’s controversial and ambitious proposals make clear that we can’t rule it out in our efforts to understand quantum gravity.

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