Will_Sawin comments on Dutch Books and Decision Theory: An Introduction to a Long Conversation - Less Wrong

19 Post author: Jack 21 December 2010 04:55AM

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Comment author: Will_Sawin 21 December 2010 06:29:56PM 0 points [-]

The Bayesian doesn't know Z is stronger than Y. He can't even read all of Z. Or if you compress it, he can't decompress it.

P(Y|Z)<1.

Comment author: AlephNeil 21 December 2010 06:40:36PM 0 points [-]

P(Y|Z)<1

If you say that then you're conceding the point, because Y is nothing other than the conjunction of a carefully chosen subset of the trivial statements comprising Z, re-ordered so as to give a proof that can easily be followed.

Comment author: Will_Sawin 21 December 2010 06:56:06PM 0 points [-]

Figuring out how to reorder them requires mathematical knowledge, a special kind of knowledge that can be generated, not just through contact with the external world, but through spending computer cycles on it.

Comment author: [deleted] 21 December 2010 07:25:25PM 0 points [-]

Yes. It's therefore important to quantify how many computer cycles and other resources are involved in computing a prior. There is a souped-up version of taw's argument along those lines: either P = NP, or else every prior that is computable in polynomial time will fall for the conjunction fallacy.

Comment author: AlephNeil 21 December 2010 06:33:35PM 0 points [-]

Imagine he has read and memorized all of Z.

If you want to make it a bit less unrealistic, imagine there are only, say, 1000 difficult proofs randomly chopped and spliced rather than a gazillion - but still too many for the subject to make head or tail of. Perhaps imagine them adding up to a book about the size of the Bible, which a person can memorize in its entirety given sufficient determination.

Comment author: Will_Sawin 21 December 2010 06:53:58PM 0 points [-]

Oh I see. Chopped and spliced. That makes more sense. I missed that in your previous comment.

The Bayesian still does not know that Z implies Y, because he has not found Y in Z, so there still isn't a problem.