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CronoDAS comments on New report: Intelligence Explosion Microeconomics - Less Wrong
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Nothing that has physically happened on Earth in real life, such as proteins folding inside a cell, or the evolution of new enzymes, or hominid brains solving problems, or whatever, can have been NP-hard. Period. It could be a physical event that you choose to regard as a P-approximation to a theoretical problem whose optimal solution would be NP-hard, but so what, that wouldn't have anything to do with what physically happened. It would take unknown, exotic physics to have anything NP-hard physically happen. Anything that could not plausibly have involved black holes rotating at half the speed of light to produce closed timelike curves, or whatever, cannot have plausibly involved NP-hard problems. NP-hard = "did not physically happen". "Physically happened" = not NP-hard.
Um... doesn't it take exponential time in order to simulate quantum mechanics on a classical computer?
Yes (At least that's the general consensus among complexity theorists, though it hasn't been proved.) This doesn't contradict anything Eliezer said in the grandparent. The following are all consensus-but-not-proved:
P⊂BQP⊂EXP
P⊂NP⊂EXP
BQP≠NP (Neither is confidently predicted to be a subset of the other, though BQP⊂NP is at least plausible, while NP⊆BQP is not.)
If you don't measure any distinctions finer than P vs EXP, then you're using a ridiculously coarse scale. There are lots of complexity classes strictly between P and EXP, defined by limiting resources other than time-on-a-classical-computer. Some of them are tractable under our physics and some aren't.
Is that just that we don’t know any better algorithms, or is there a proof that exptime is needed?
I really don't know; some Wikipedia browsing suggests that there's a proof, but I'd rather have a statement from someone who actually knows.