So this is a bit of a duplicate: Is the universe fully transparent to gravitons?

[Paul Colby]

You're missing the point.

Perhaps I am. Maybe you could explain further. In the usual naive gravitational field theory, energy is exchanged with mater in quanta, $E=\hbar \omega$. In a low energy test, an atom could absorb a graviton quanta. Now, I'd be the first to agree that the cross section of such a reaction is exceedingly small making it impractical to detect. However, the process is allowed and not classical as far as I can tell.

 

[PeterDonis]

In a low energy test, an atom could absorb a graviton quanta.

Yes, but we have no feasible way of testing for this, now or in the foreseeable future. Or for any other process where the quantum theory would make a different prediction from classical GR, which is the classical limit of the quantum theory.

But now consider a process such as the detection of a gravitational wave by LIGO. We could, in principle, try modeling this using the non-renormalizable spin-2 quantum field theory. But we would get the same prediction as for classical GR, which is the classical limit of the quantum theory. So we can't use this kind of test to test the quantum field theory.

the process is allowed and not classical as far as I can tell.

Yes. I have not said otherwise. I was not saying that there can't be any non-classical processes involving gravity.

 

[Algr]

Now place a black hole between them. I would expect -= and again, there's no theory so no way to do the calculation - the detector to stop seeing the emitter.

Please forgive the question, but can gravitons escape a black hole? If not, then how do black holes attract other objects?

 

[PeterDonis]

can gravitons escape a black hole?

We already have an open thread on this (and not the first one we've had):

https://www.physicsforums.com/threads/why-can-gravity-escape-from-a-black-hole.1047005/