Do Astrophysical Black Holes Contain CTCs?

[bIcyt265]

TL;DR

Is it plausible that astrophysical black holes contain CTCs?

I've been seeing popularizations recently that talk as though it's widely accepted that astrophysical black holes contain CTCs. Example: https://www.abc.net.au/news/2023-01...me-machines-yes-but-there-s-a-catch/101822002

Is this accurate? Eternal black hole solutions contain all kinds of features that aren't expected to be physical for black holes that form by gravitational collapse. For example, the Schwarzschild spacetime has an Einstein-Rosen bridge and a white hole. The fact that the Kerr solution has CTCs doesn't mean that astrophysical black holes necessarily contain them.

On the other hand, I would have said the same thing about Cauchy horizons until Dafermos's recent work.

Are the current best formulations of chronology protection set up in such a way that CTCs inside an astrophysical black hole would be counterexamples, or are they set up so that CTCs behind an event horizon don't count?

 

[PeterDonis]

I've been seeing popularizations recently that talk as though it's widely accepted that astrophysical black holes contain CTCs.

Popularizations are not a good place to go to learn actual physics.

On the other hand, I would have said the same thing about Cauchy horizons until Dafermos's recent work.

Can you give a reference?

 

[Ibix]

Well, if OP prefers us to guess what (s)he wants to talk about, references 6-9 in https://arxiv.org/abs/1406.7253 seem likely to be relevant. Haven't looked to see if they're on arxiv.

 

[martinbn]

On the other hand, I would have said the same thing about Cauchy horizons until Dafermos's recent work.

This may be unexpected but it is only $C^0$-stability of the Cauchy horizon of Kerr. The usual form of the strong censorship is still expected to hold.

 

[pervect]

TL;DR Summary: Is it plausible that astrophysical black holes contain CTCs?

I've been seeing popularizations recently that talk as though it's widely accepted that astrophysical black holes contain CTCs. Example: https://www.abc.net.au/news/2023-01...me-machines-yes-but-there-s-a-catch/101822002

Is this accurate? Eternal black hole solutions contain all kinds of features that aren't expected to be physical for black holes that form by gravitational collapse. For example, the Schwarzschild spacetime has an Einstein-Rosen bridge and a white hole. The fact that the Kerr solution has CTCs doesn't mean that astrophysical black holes necessarily contain them.

On the other hand, I would have said the same thing about Cauchy horizons until Dafermos's recent work.

Are the current best formulations of chronology protection set up in such a way that CTCs inside an astrophysical black hole would be counterexamples, or are they set up so that CTCs behind an event horizon don't count?

There's been a lot of work on the interior geometry of actual astrophysical black holes, but it's unclear to me if there is a generally accepted interior solution.

Google finds, for instance, Hamilton's "The interior structure of rotating black holes 1. Concise derivation", https://arxiv.org/abs/1010.1269. I know I've seen other papers, but I don't recall them - the google search that gave this interesting result was to try to bump my memory. The other papers I recall seeing were not so ambitious.

So, are the results of a google search "generally accepted". Probably not, but one could get lucky :).

This paper builds on Poisson's and Israel's work on mass inflation. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.63.1663. This is a more established paper with a high citation count. Is this paper "generally accepted"? Hard to say.

Personal note - while I understand bits and pieces, I don't feel I have a good grasp on the "mass inflation" concept.

In general, I'm fairly sure those trying to take a hard skeptical look at the problem would like to see experimental confirmation. But the event horizon is pretty effective at hiding the interior geometry.