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Comment by maffydub | Hacker News Reader

(I am not a physicist.) One thing I've struggled with around black holes is what it means for anything to fall into a black hole.

From a reference frame outside the black hole, observing an object falling into the black hole, don't we observe time slowing down as the object approaches the event horizon? In this reference frame, does it ever cross the event horizon, or does it just asymptotically approach it? If it doesn't cross the event horizon, how can anything ever fall into the black hole?

(From the reference frame of the object falling into the black hole, my understanding was that the event horizon shrinks away from you as you approach it.)

Please correct/inform me!

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The object has physically fallen through the event horizon and long disintegrated but the imprint of its falling toward the event horizon is slowing down to the outside observer. The falling object emits photons along the way which are what the observer sees. These photons of the falling object shining toward the observer have to travel greater and greater distance in the warped spacetime as the object getting near the event horizon so the photons appear to slow down. The spacetime is being "stretched" (warped) more as getting closer to the blackhole. The event horizon is at the point where the spacetime is "stretched more than" the distance the photons can travel to come out.

(also not a physicist) I think you're correct that objects falling into a black hole never cross the event horizon from our reference frame, but at the same time the light from the object red shifts towards zero energy as it approaches the event horizon as well.

Thanks!

Does the fact that the light red shifts towards zero energy mean that the information has been lost, or just that you can't observe it _at_the_moment_?

If the black hole then shrinks due to Hawking radiation, what happens to the object that _never_quite_fell_into_ the black hole?

If it hasn't yet fallen into the black hole, presumably its light becomes slightly-less-red-shifted once more, meaning that you can observe its information again?

There is a somewhat recent theory that supports this idea. It is unclear whether or not things actually fall-in, but the idea is that the entire surface is a hologram, and the surface alone is sufficient to describe the entire contents. (Thus preventing any information loss).

Much better described here:

https://www.youtube.com/watch?v=2DIl3Hfh9tY

Good video - thanks!

I didn't quite follow how information came back out of the black hole as it shrank - is it "encoded" on the Hawking radiation?

I believe Hawking thought so, but that's just one possible explanation. Others think it all escapes at the very end.

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