# Warrigal comments on Crisis of Faith - Less Wrong

57 10 October 2008 10:08PM

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Comment author: [deleted] 25 August 2009 10:30:16AM 6 points [-]

The argument in this post is precisely analogous to the following:

Bayesian reasoning cannot actually predict anything. Choose priors that result in the posterior for MWI being greater than that for Copenhagen, and it says you should believe MWI; choose priors that result in the posterior for Copenhagen being greater than that for MWI, and it says you should believe Copenhagen.

The thing is, though, choosing one's own priors is kind of silly, and choosing one's own priors with the purpose of making the posteriors be a certain thing is definitely silly. Priors should be chosen to be simple but flexible. Likewise, choosing a language with the express purpose of being able to express a certain concept simply is silly; languages should be designed to be simple but flexible.

Comment author: 25 August 2009 10:38:47AM *  8 points [-]

It seems to me that you're waving the problem away instead of solving it. For example, I don't know of any general method for devising a "non-silly" prior for any given parametric inference problem. Analogously, what if your starting language accidentally contains a shorter description of Copenhagen than MWI?

Comment author: [deleted] 27 August 2009 12:56:02AM 1 point [-]

If you're just doing narrow AI, then look at your hypothesis that describes the world (e.g. "For any two people, they have some probability X of having a relationship we'll call P. For any two people with relationship P, every day, they have a probability Y of causing perception A."), then fill in every parameter (in this case, we have X and Y) with reasonable distributions (e.g. X and Y independent, each with a 1/3 chance of being 0, a 1/3 chance of being 1, and a 1/3 chance of being the uniform distribution).

Yes, I said "reasonable". Subjectivity is necessary; otherwise, everyone would have the same priors. Just don't give any statement an unusually low probability (e.g. a probability practically equal to zero that a certain physical constant is greater than Graham's number), nor any statement an unusually high probability (e.g. a 50% probability that Christianity is true). I think good rules are that the language your prior corresponds to should not have any atoms that can be described reasonably easily (perhaps 10 atoms or less) using only other atoms, and that every atom should be mathematically useful.

If the starting language accidentally contains a shorter description of Copenhagen than MWI? Spiffy! Assuming there is no evidence either way, Copenhagen will be more likely than MWI. Now, correct me if I'm wrong, but MWI is essentially the idea that the set of things causing wavefunction collapse is empty, while Copenhagen states that it is not empty. Supposing we end up with a 1/3 chance of MWI being true and a 2/3 chance that it's some other simple thing, is that really a bad thing? Your agent will end up designing devices that will work only if a certain subinterpretation of the Copenhagen interpretation is true and try them out. Eventually, most of the simple, easily-testable versions of the Copenhagen interpretation will be ruled out--if they are, in fact, false--and we'll be left with two things: unlikely versions of the Copenhagen interpretation, and versions of the Copenhagen interpretation that are practically identical to MWI.

(Do I get a prize for saying "e.g." so much?)

Comment author: 27 August 2009 01:03:19AM 10 points [-]

(Do I get a prize for saying "e.g." so much?)

Yes. Here is an egg and an EEG.