Referring to this question, is there any information that can leave black holes? Are they causing a permanent information loss in our Universe?

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    $\begingroup$ Can you clarify what you mean by "information"? It sounds like you are asking if there's an Alexandrian library that needs rescuing. ;-) $\endgroup$ Sep 24 '13 at 20:05

Information cannot "leave" the black hole. There is no way (by our current framework of physics) that an entity inside the event horizon can send a signal out.

However, entropy can leave. The black hole has entropy proportional to its surface area, and this roughly corresponds to "the number of ways that black hole could have been created". The surface area decreases due to Hawking radiation, so it can release entropy back to the universe. Of course, the growth rate due to infalling mas is usually many orders of magnitude more than the shrinkage.

  • $\begingroup$ I'm not sure I understand the distinction. Suppose I have a machine which is programmed to send either a 1 or a 0 in 1 seconds time (but take care not to know which), and I drop it so that it crosses the event horizon after 0.5 seconds of its own proper time is that one bit of information not part of the "number of ways that black hole could have been created". So the black hole will gain entropy as the machine falls, including the one bit of entropy corresponding to its internal state. When the black hole decays that information/entropy willl emerge. Is this right? $\endgroup$ Sep 17 '20 at 13:12
  • $\begingroup$ @steve Entropy is not information. The entropy will leave in the form of some particles. The information will be lost forever. Entropy is not a genealogy of information. $\endgroup$ Sep 18 '20 at 7:51

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