[amluto]

Because quantum mechanics _really_ does not like destroying information. Mangling information beyond recognition is just fine, but the laws of quantum mechanics are very insistent that, if you have a complete description of the state of the universe, you can solve the equations backwards and figure out what happened in the last. When you throw in a black hole following Hawking’s rules, or any other device that irretrievably chews things up and spits them out in a way that can’t, even in theory, be undone, quantum mechanics breaks.

[kstrauser]

Got it, thanks! That seems unintuitive to me (which is pretty much the summary of QM as far as I can tell), but I trust that some pretty clever people are convinced of this.