Alex_Altair comments on An Intuitive Explanation of Solomonoff Induction - Less Wrong

53 Post author: Alex_Altair 11 July 2012 08:05AM

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Comment author: kilobug 09 July 2012 01:09:38PM 4 points [-]

After reading it fully, I've another, deeper problem with this (still great) article : Bayes' theorem totally disappears at the end. Hypothesis that exactly match the observation bitwise have a fixed probability (2^-n where n is their length), and those which are off even by one bit is discarded. There is no updating of probabilities, because hypothesis are always right or wrong. There is no concept left of an hypothesis that'll predict the position of an electron using a probability distribution, and there is no room for an hypothesis like "the coin will fall heads 75% of times, tails 25% of time".

That's both a problem for the article itself (why even speak of Bayes' theorem, if at the end it doesn't matter ?) and to find the "truth" about the universe in a quantum world (even if you accept MWI, what you'll actually observe in the world you end up being in will still be random).

I understand that going into the full details on how to handle fuzzy hypothesis (like, algorithms who don't just output one result, but different results and the probability of each) would make the article even longer, but it would still be a good thing to address those issues somewhere, IMHO.

Comment author: Alex_Altair 09 July 2012 04:26:51PM 3 points [-]

You are pretty much correct.

The causal reason that Bayes' theorem is in the article is because Luke wrote that part before I was involved. If I had written it from scratch, I probably wouldn't have included it.

But I think it's reasonable to include it because this is an article for laymen, and Bayes' theorem is a really important piece to have your knowledge of rationality built around. Furthermore, the discovery of Solomonoff induction was motivated by the search for objective priors, which is a Bayes' theorem thing.

But you're exactly correct that hypotheses either match or they don't. The updating of probabilities occurs when you renormalize after eliminating hypotheses. Also, I've thought about it for a while and concluded that no modification is needed to represent probabilistic hypotheses. I may write a piece later about how Bayes' theorem is consistent with Solomonoff induction.