[uoaei]

Bit of an aside, but:

> But physicists seek the more fundamental, quantum theory of gravity that underlies Einstein’s picture; it’s this quantum gravity theory that governs extremes like the Big Bang and black holes. And one way to inch toward this complete theory is to study quantum fluctuations in the space-time fabric.

I'm uncomfortable with the implicit framing that quantum gravity is The One True Theory and we just need to figure out how to formalize it. I'm sure this comes from the author and not the researcher, maybe something was lost in translation from the technical to the colloquial, but nonetheless it is still inaccurate to say that there is any kind of certainty that this is the right path forward. (Ditto for dark matter and dark energy, though those could more accurately be described as lacks of models than models per se.)

[klyrs]

My understanding is that quantum gravity is a gaping hole in our theoretical understanding of the universe, and until that hole is plugged, we have no hopes of finding a One True Theory. That's quite different from quantum gravity being The theory.

[uoaei]

What I was trying to get at is that gravity may not even be quantized. The insistence that it act like the other three fundamental forces is a holdover from earlier interpretations of physics but in retrospect there's still no solid reason to assume it has to be quantum at all.

[ndsipa_pomu]

What other approaches are there that wouldn't lead to a quantum theory of gravity?

[uoaei]

There is more focus of late on theories of "emergent gravity", i.e., that gravity is not a fundamental force. The most interesting one to me is so-called "entropic gravity", which also resolves the issues plaguing the theory of dark matter and gives credence to MOND. Such theories have been long derided by old-school physicists raised in the golden era of quantum mechanics (and their acolytes), but have surprisingly powerful explanatory power that other theories cannot achieve without tacking on seemingly arbitrary or else otherwise unmotivated factors. Dark matter especially has always been suspect to me, since even after all this time, it is defined as little more than "the gap between our models and observations" with no strong underpinnings that would explain its existence in satisfying ways.

I am not affiliated with this blog in any way but find the arguments compelling: https://tritonstation.com/

Here's an interview with a researcher who is also trying to move beyond quantum formalisms for spacetime vis a vis gravity: https://www.quantamagazine.org/the-physicist-who-bets-that-g...