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I may have posted this before, but it’s a really fun read:<\/p>\n
\nThe firewall paradox involves a thought experiment where Alice\u2014it\u2019s always Alice\u2014sits outside of a black hole waiting for it to mostly but not completely evaporate, and scooping up all the Hawking radiation it emits as it does so. For a black hole the mass of our sun, this would take about 1067<\/sup> <\/span>years (we\u2019ll assume Alice has a really long grant). Then, Alice routes all the photons of Hawking radiation into her quantum computer, where she processes them in such a way as to prove that they <\/span>did<\/em> <\/span>encode information about the infalling matter. Then, as the final step, Alice jumps into the black hole. The clincher is that, <\/span>if<\/em> <\/span>you combine all the ideas about black holes that had previously been accepted, you can now make a firm prediction that Alice will encounter an end of spacetime right at the event horizon (in the physicists\u2019 colorful language, she\u2019ll \u201chit a firewall and burn up\u201d). But this is totally contrary to the prediction of general relativity, which says that Alice shouldn\u2019t notice anything very special at the event horizon, and should only encounter an end of spacetime at the <\/span>singularity<\/em>.<\/p>\n
There are various ways out of this that aren\u2019t very satisfying: you could deny that information escapes from black holes. You could say that general relativity is wrong, and what we\u2019d previously called black holes are really just firewalls. You could argue that what happens inside a black hole isn\u2019t even within the scope of science\u2014since much like life after death, it\u2019s not empirically testable by anyone who \u201cremains on this side.\u201d Or\u2014and this seems like the \u201cconservative\u201d option!\u2014you could admit that Alice can <\/span>create<\/em> <\/span>a firewall by doing this crazy processing of the Hawking radiation, but insist that, if she doesn\u2019t do the processing, then she\u2019ll pass through the event horizon just like general relativity always said she would. But if you take this last option, then what Alice perceives as the structure of spacetime\u2014whether she encounters an event horizon or a firewall\u2014will depend on what she programmed her quantum computer to do<\/em>.<\/p>\n<\/blockquote>\n