Is gravity fundamentally quantum?

Will empirical evidence arise through experiments definitively determining if gravity is fundamentally quantum? Or will evidence prove that gravity cannot be quantized into Graviton-like particles? Multiple experiments have been proposed, and some are currently underway which may answer this fundamental question. Market resolves to YES if definitive proof arises pointing towards a fundamentally quantum nature of gravity by the end of 2040. Market resolves to NO if definitive proof arises pointing towards a fundamentally non-quantum gravity by the end of 2040. Market resolves to N/A if no proof arises for either hypothesis by the end of 2040.

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As it was in 2001, it will continue to be in 2040. We have very very good reason to believe gravity is quantum, and to think all alternatives are doomed to fail, but it's near impossible to see empirical evidence or a no-go theorem.

predicts YES

@Najawin Recent very promising experiments have found ways to rule out certain aspects, if they succeed.

However, like you said, measuring a single Graviton is pretty much impossible:

But I think some key aspects of gravity could be learned through some of the above experiments over the next few years which could point us towards a fundamentally quantum or non-quantum gravity.

@Supermaxman Wait, are we unironically posting Hossenfelder videos these days? She's a crank. Okay, that's slightly unfair of me. She's as close to the crank/not crank line as you can be without actually being a crank. Do not trust anything she says. She isn't necessarily wrong, but she's so heterodox in all of her views, and her epistemology is so broken that you can't use her to update your beliefs in any meaningful sense.

And, you know, I'm glad that the press release is such a fan of the experiment. But, well, it would be, wouldn't it? The reality is more complicated. The two original papers (, suggesting this experiment were not particularly well informed of some of the very specific nuances on this subject, and as a result there are some gaps in the experiment that weren't publicized as much as the original hype. (Indeed, the second paper linked there is attempting to offer a very general argument that runs into an analogous counter argument to the one in the Huggett and Callender paper, if you're careful about collapses vs entangled states.) See, (v2 was withdrawn for copyright reasons, not because the author retracts the work, you can find v3 elsewhere),, and

@Najawin what is your take on the recent work by Oppenheim in and which do prove theoreticaly postquantum gravity may be possible and also provide setups for experiments that may verify their theories.

predicts YES

@Najawin Great info! Yes, I am not particularly a fan of Hossenfelder’s strange belief system, but I like to listen to a few different people and she brought up these experiments. Will definitely read these, appreciate everything! I am particularly cautious with preprints in physics though (with CS/AI it’s a bit different), definitely waiting for some peer review as well.

@rogerplanck I'm with Rovelli on this one.