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There have been some lengthy discussions, here and here (among others), about whether, to the distant observer, black holes form in a finite time or an object falls into a black hole in a finite time. To the extent that readers understood and addressed the OPs' questions, it would seem that things can collapse to a point that it's very much like a black hole, a "collapsar", and can be treated like one and astronomers talk about it as if it were a black hole. But still stuck outside the event horizon.

But nobody seems to have explored some of the implications of that. The free-falling observer falls through the event horizon and hits the singularity in a finite amount of proper time. The distant observer never actually "sees" (or could infer by measurement) that the free-faller reached the event horizon, but eventually will see the stars run out of fuel and wink out as the universe continues to expand, and the black holes evaporate by Hawking radiation and disappear, and all of that before, in the external flat-space reference frame, the free-faller crosses the event horizon.

At first glance, maybe we can't just assume that, from the free-faller's perspective, the event horizon is going to statically exist long enough to reach it. But GR is a classical theory that exists without that. So if, in distant coordinates, it takes an infinite amount of time for the free-faller to go through the event horizon, how long does it take for the free-faller to reach the singularity? More than infinite?

It seems like a lot has been said about what's going on inside the event horizon that might just be null and void. Would quantum gravity explain what happens at the singularity? Irrelevant, because there is no singularity. Is information lost when it crosses the event horizon? Irrelevant, because it doesn't cross the event horizon--we might not be able to get it back, but it's still stuck outside. What does it actually mean for time to become spacelike and the spatial dimensions to become timelike? Maybe it literally is nonsense, like the advanced-wave solutions in EM which are mathematically valid but physically meaningless. Maybe it's a clue.

Understand that I'm not questioning the validity of GR, just the popular understanding of it vis-a-vis black holes and event horizons.

To make this a specific question rather than a call for discussion, is it just physically meaningless to talk about what happens "inside" of a black hole?

I suspect this will be an unpopular perspective.

Qmechanic
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Greg
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1 Answers1

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It seems that nobody can answer your question. Here are some elements which might help for the answer. Many open questions are left, but you may decide yourself if some of the following elements may be interesting for your reflection:

  1. The infalling observer reaches the event horizon of the Schwarzschild metric not earlier than at the "end of time" of the universe. That means, if from his point of view he crosses the event horizon within finite time, all outside observers will agree that he will cross the event horizon "never" (= at the end of our time).

  2. Intuitively, "the end of time" seems to be no well specified time indication, but it might be interesting to consider the end of time as a moment which is quite precise (at least from the point of view of the reference frame of the infalling observer). If so, we could say that all infalling observers are crossing the event horizon exactly at the same moment, and that the existence beyond the event horizons (from the point of view of all infalling observers) begins after our time.

  3. A consequence of the fact that the infalling observer is reaching the event horizon only at the end of time might be that all information of the infalling observer is remaining outside of the event horizon, and that there is no infalling information (the infalling observer is "stripping off" all information before entering beyond the event horizon).

  4. Another question which is important is the one if the entropy of infalling particles is zero at the event horizon. This question arises also in models of the Big Crunch.

Moonraker
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