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Suppose an object A is traveling towards black hole. For an observer outside it looks like A almost reached even horizon and is still trying to reach it.

So from point of view of an observer all the matter is on even horizon (we don't see all of it due to severe severe redshift making black holes invisible in all EM spectrum that we can detect). And all observers being equal, this view is also correct.

So which one is true, did A cross horizon or not? Or somehow both is true? Which leads to this question do blackholes contain matter? Or they are just a void out in both time and space. Because for all practical and theoretical purposes all curved spacetime ends at event horizon. We simply don't know what lies beyond.

Qmechanic
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sakura
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    That question has been anwered many times before, as you can see when using the search function. – Yukterez Feb 19 '20 at 19:14
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    If you drive across a border but nobody sees you do it, did you actually cross it? Of course you did. If you fall into a black hole, you’re going to eventually know it, and it isn’t going to take long according to the way you experience time. Who cares what outsiders see? – G. Smith Feb 19 '20 at 21:16
  • There is nothing in the mathematics of GR that suggests it should break down at the event horizon and not be valid well inside. (You can expect certain people to disagree. I think they’re wrong.) Occam’s Razor tells us to make the simplest assumption compatible with what we know, and the simplest assumption is that GR is valid inside and thus we have a very good idea of what is going on. – G. Smith Feb 19 '20 at 21:26
  • Locally, it is quite boring. Local spacetime inside, except at the singularity, is no different from local spacetime outside. In a sufficiently small region, they are Minkowskian through first order in Riemann normal coordinates. The curvature gets greater as you approach the singularity, but the curvature can be survivable even well inside the horizon if the hole is massive enough. – G. Smith Feb 19 '20 at 21:27
  • As far as I know, this is the conservative, mainstream view. – G. Smith Feb 19 '20 at 21:33
  • If you create it with a single Kugelblitz - see https://www.youtube.com/watch?v=v3hd3AI2CAA&t=4m26s - it is hollow, but if it is made of a collapsing star it isn't. In the frame of the external observer the radius also only converges to the event horizon radius, but it never reaches it, only after an infinite amount of coordinate time (and a finite proper time of the infalling particles) – Yukterez Feb 19 '20 at 22:06
  • @sakura Despite a super wide spread misconception, there is no energy flow through the horizon. See section 4.1 on pages 43-44 in this publication of two accomplished mathematicians (Indiana University): https://www.newton.ac.uk/files/preprints/ni14098.pdf – safesphere Feb 19 '20 at 23:35

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