benelliott comments on Edward Nelson claims proof of inconsistency in Peano Arithmetic - Less Wrong

13 Post author: JoshuaZ 27 September 2011 12:46PM

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Comment author: benelliott 01 October 2011 12:28:46AM *  1 point [-]

My knowledge of complexity theory is very limited, but I thought exponentiation could be done in polynomial time. Is that incorrect, or am I misunderstanding Nelson's argument (please don't tell me he also doubts complexity theory, we must be allowed some fun :P).

EDIT: Yes, I was wrong, the claim of polynomial time in the length of b may well be too strong, but it does seem to use less than 2^b. I think I can use the position system to compute 2^b in O(b^2) steps, which seems to lead us straight from accepting multiplication to accepting exponentiation.

Comment author: [deleted] 01 October 2011 01:14:25AM 1 point [-]

I think so, in positional notation. That's what I was alluding to with my O(log log k) comment. But there is no polynomial time algorithm to reduce 2^n to a tally number (obviously).

I once read something by Nelson about the polynomial hierarchy in complexity theory, but I can't find it now.