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Black holes are said to be composed of two parts:

  • A singularity at the center, where all the mass of the black hole is condensed in a point of zero volume.
  • A black and empty ball delimited by the event horizon.

Also, relatively to an observer outside the black hole, the time for a particle inside the black hole (inside the event horizon) is stopped/frozen.

Suppose we had a particle very similar to photons but which wasn't affected by the gravitational force. Using this particle as our light we could see inside the black hole.

What would we see? We would see that particles who fall in the black hole become slower and slower because the more we come close to the black hole and the more time slows down. And once particles reach the event horizon, they stop completely, as time freezes.

So my question is: How can particles reach the singularity if time stops at the event horizon?

Scientists always say that, when a star collapses into a black hole, all the matter will be compressed in a singularity... But how can this singularity form if time stops at the event horizon?

Quantum Force
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  • I've suggested what seems to me an obvious duplicate, and there are many other related posts on this site (though getting the right search terms to find them isn't trivial!). If you aren't happy that my suggested duplicate answers your question reply to this comment and I'll withdraw my clse vote. – John Rennie Mar 28 '15 at 11:07
  • @John Rennie: Thanks. I've read the question you suggested as well as two others. So it seems that the answer is: nobody knows ? In this question http://physics.stackexchange.com/questions/21319/how-can-anything-ever-fall-into-a-black-hole-as-seen-from-an-outside-observer/21357#21357 the best answer says that nothing ever passes through the event horizon so nothing every reach the singularity ; while in this answer http://physics.stackexchange.com/questions/82678/does-someone-falling-into-a-black-hole-see-the-end-of-the-universe the best answer says that matter does reach the singularity. – Quantum Force Mar 28 '15 at 12:38
  • Finite time falling: https://physics.stackexchange.com/a/628883/226902 and https://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html – Quillo Aug 20 '23 at 08:10

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