general relativity - Could gravity be an emergent property of nature?

Sorry if this question is naive. It is just a curiosity that I have.

Are there theoretical or experimental reasons why gravity should not be an emergent property of nature?

Assume a standard model view of the world in the very small. Is it possible that gravity only applies to systems with a scale large enough to encompass very large numbers of particles as an emergent property?

After all: the standard model works very well without gravity; general relativity (and gravity in general) has only been measured at distances on the millimeter scale.

How could gravity emerge? For example, it could be that space-time only gets curved by systems which have measurable properties, or only gets curved by average values. In other words that the stress-energy tensor has a minimum scale by which it varies.

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Edit to explain a bit better what I'm thinking of.

1. We would not have a proper quantum gravity as such. I.e. no unified theory that contains QM and GR at the same time.


2. We could have a "small" (possibly semi-classical) glue theory that only needs to explain how the two theories cross over:
   
   
   
   
   • the conditions and mechanism of wave packet reduction (or the other corresponding phenomena in other QM interpretations, like universe branching or decoherence or whatnot)
   
   
   • how this is correlated to curvature - how GM phenomena arise at this transition point.
   
   
   
   

Are there theoretical or experimental reasons why such a reasoning is fundamentally incorrect?

Answer

I'm not an expert in gravity, however, this is what I know.

There's a hypothesis about gravity being an entropic property. The paper from Verlinde is available at arXiv. That said, I would be surprised for this to be true. The reason is simple. As you probably know, entropy is an emergent property out of statistical probability. If you have non-interacting, adimensional particles into one half of a box, with the other half empty and separated by a valve, it's probability, thus entropy, that drives the transformation. If you look at it from the energetic point of view, the energy is exactly the same before and after the transformation. This works nicely for statistical distribution, but when you have to explain why things are attracted to each other statistically, it's much harder. From the probabilistic point of view, it would be the opposite: the more degrees of freedom your particles have, the more entropy they have. A clump has less degrees of freedom, hence has less entropy, meaning that, in a closed system, the existence of gravity is baffling. This is out of my speculation, and I think I am wrong. The paper seems to be a pleasure to read, but I haven't had the chance to go through it.