Roy Kerr: Do Black Holes Have Singularities?

Re:Roy Kerr: Do Black Holes Have Singularities? by eigenket on Friday December 15, 2023 @07:24AM (#38653449)

My understanding (which is highly limited, I am a researcher in quantum information but quantum gravity is very far out of my reach) is that this essentially gives you information about degrees of freedom of "stuff" (I guess quantum fields) that has been thrown into the black hole. I.e. you throw a diary with information in, and you can (theoretically) learn that information from the Hawking radiation if you absorb enough of it.

This is quite different from being able to probe the space-time structure inside (i.e. ask questions like is there a real singularity in there).

If you think about what you'd need there, you need the opposite of what they have in the FAQ, you would need operations in the interior to be able to create a particle on the exterior in order to build a "telescope" to look inside and I'm pretty sure this is ruled out even in this proposal.

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Re:Roy Kerr: Do Black Holes Have Singularities? by kromem on Friday December 15, 2023 @09:12PM (#38661131)

Actually that's what their section 6.3 is all about, how if you sent an observer inside the event horizon measurements could influence the outside.

It just admits that the feasibility of this is ridiculous with my favorite line of the paper:

> Physically this seems absurd, as it allows a measurement inside a black hole to produce a record which stays outside, but we are not claiming that any effective-description observer could actually implement this unitary.

But I agree that there's a big difference between the plausibility of measuring the 'stuff' vs it's spacetime configuration - that was a great point.

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