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A little OT: do the information theory based proofs of limits on how effective compression can be also prove that backwards time travel is impossible?

If backwards time travel were possible then your "compression algorithm" could simply be deleting the file. To recover the file go back in time to before it was deleted and make a copy.

With this you can "compress" giant files down to just a short description of a place and time where the file was on your computer.

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Interesting idea, but you're not getting any entropy for free by going back in time. If you wanted to map every possible file of a set length to a specific time and location where it's stored, you'd still need, in general, the same number of bits as you would for the file itself, because you'd have to describe that many distinct time/location pairs.

Backwards time travel is perfectly possible, but perhaps not in our actual reality, but in a simulation of our universe, which would get you the data you want.

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