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From the perspective of the surface of a collapsing star, if you were riding it in as it formed a black hole, what would you observe looking out into the rest of the universe? As you approached the forming event horizon, would time dilation make the universe outside appear to speed up? Would you see a distant galaxy rotate faster and faster? And would this time dilation increase without limit as you approached the event horizon? And if so does this mean that in some sense, no black holes have actually had enough time to form yet, since an observer riding the surface of the black hole would witness events arbitrary far into the future before crossing the event horizon? Can someone please help me understand this perspective better?

Thank you!

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Nope, not at all! If you were riding the surface of a collapsing star, you'd see the universe outside be substantially distorted from the bending of light by the star's gravity, but you wouldn't see any extreme time dilation effects. Everything would look normal to you (up to the distortion of light) until your inevitable death at the singularity.

Your thinking might be coming from the fact that to an observer hovering outside the black hole, you would appear to slow down more and more as you enter the black hole (and in fact, that observer would never actually see you fall in!). But the configuration isn't symmetric: the fact that the outside observer sees you slowing down doesn't imply that you should see everything outside speeding up. The reason for this asymmetry is the fact that the horizon is not symmetric: things can go in, but they can't climb out. So if you were to shoot light signals at your friend outside the black hole, say, your friend would receive them with more and more delay as you get closer to the event horizon because it's harder and harder for them to get out to them. But if your friend were shooting light signals down to you, those signals have no problem getting to you, even once you're inside the black hole.

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  • $\begingroup$ Thank you for the response! Is it not true though that one experiences a relative slowing of time in the presence of a strong gravitation field? $\endgroup$ – Chris Michael Sullens Feb 10 '16 at 17:57
  • $\begingroup$ No problem! And yes, it is true that there would be some time dilation effects due to the gravitational field, but from the perspective of an infalling observer, these effects are not huge. (An observer hovering just outside the horizon, however, would see very large time dilation effects due to the very large acceleration they would need to avoid falling in.) $\endgroup$ – Sebastian Feb 10 '16 at 18:07

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