Path: ...!news.mixmin.net!news2.arglkargh.de!news.karotte.org!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: ram@zedat.fu-berlin.de (Stefan Ram) Newsgroups: sci.physics.research Subject: Falling into a black hole Date: Sun, 26 May 2024 16:46:52 PDT Organization: Stefan Ram Lines: 72 Approved: Jonathan Thornburg [remove -color to reply]" X-Trace: individual.net 4GdWVjbRvD9QAcblUMScSw91g2RD0wOqT8DhS1SNNvKJKcqPbtaETXvcWx Cancel-Lock: sha1:KV6chw6Ga8T8sS+1UPIaDiVXbZQ= sha256:UoVkuazN5d/ur3s7nA2fuz58hUyI6V8Xfl8aqayYLIk= X-Forwarded-Encrypted: i=2; AJvYcCXmi0X5QvMbGege8EVBsytvBQJcI549GpqhNTJGoR9qDZe3nLwW4RthZbl1ltSWaK4bDEBwg/1eQbrd0eEbvKOQ9r3eH3DEJrg= X-Orig-X-Trace: news.uni-berlin.de XDqeWybRmT7chovGm65nBwB5pqLtCDQYfTtz29i7p4k/v9 X-Copyright: (C) Copyright 2024 Stefan Ram. All rights reserved. X-No-Archive-Readme: "X-No-Archive" is set, because this prevents some X-No-Html: yes X-ZEDAT-Hint: RO Bytes: 4608 This might be a bit of a speculative question. They say that if an object falls into a black hole, it would appear to an observer at a great distance relative to the black hole that the object slows down but never actually reaches the event horizon. I'll refrain from pondering the idea that for an object near the event horizon, quantum mechanically due to the uncertainty principle, the probability of being inside the event horizon could already be greater than 0. I'm sure experts have thought about that as well. So, where was I? Ah yes, for an outside observer, the object reaches the event horizon only after an infinite amount of time has passed. On the other hand, from an outside perspective, the black hole itself could have evaporated after a finite amount of time AFAIK. What happens to the object, which from the outside appears to be waiting just short of the event horizon, after the black hole has evaporated from the point of view far from the black hole? Would we find the object outside the event horizon then? - TIA! [[Mod. note -- A few comments (I suspect the author already knows these things): > for an outside observer, the object reaches the event horizon only > after an infinite amount of time has passed It's useful to think of the infalling object as sending out continuous light (or radio) signals. As the object approaches the event horizon, these signals take longer and longer to reach a (fixed) outside observer, and the signals are more and more redshifted. This results in the effect the author described, and means that the outside observer never sees any signals emitted on or inside the event horizon. It may be useful to rephrase the above-quoted statement as: Light/radio signals from the moment the infalling object crosses the event horizon will take infinitely long to reach, and will be infinitely redshifted when they arrive at, a (fixed) outside observer. This phrasing makes it clear(er) that the effects we're describing are caused by light/radio signal propagation near the event horizon, rather than the infalling object's motion being in any way arrested. Indeed, an observer riding the infalling object itself would measure it passing through the event horizon very quickly; it's "just" that after passing through the event horizon her light/radio signals would never reach the outside observer. The time scales are interesting: For a 1-solar-mass black hole (event horizon is a few kilometers in diameter): * outside observer sees the object's radio signals infinitely redshift and cut off on a time scale of microseconds; the last photon received by the outside observer will be very low-enegy (upon reception) and have originated just before the infalling object crossed the event horizon * infalling observer reaches r=0 singularity in microseconds (but any messages from her about what it's like, will never get to the outside observer) * outside observer sees the black hole evaporate in something on the order of 10^67 years As for your actual question, what happens to things inside a black hole when it (eventually) evaporates, it's a good question. Alas, I don't think we (yet) understand quantum gravity well enough to know the answer. :( There's a brief introduction to this topic at: https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_evaporation -- jt]]