saturn comments on Ingredients of Timeless Decision Theory - Less Wrong

43 Post author: Eliezer_Yudkowsky 19 August 2009 01:10AM

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Comment author: PhilGoetz 21 August 2009 05:57:21PM *  0 points [-]

Here is what I don't understand about the free will problem. I know this is a simple objection, so there must be a standard reply to it; but I don't know what that reply is.

Denote F as a world in which free will exists, f as one in which it doesn't. Denote B as a world in which you believe in free will, and b as one in which you don't. Let a combination of the two, e.g., FB, denote the utility you derive from having that belief in that world. Suppose FB > Fb and fb > fB (being correct > being wrong).

The expected utility of B is FB x p(F) + fB x (1-p(F)). Expected utility of b is Fb x p(F) + fb x (1-p(F)). Choose b if Fb x p(F) + fb x (1-p(F)) > FB x p(F) + fB x (1-p(F)).

But, that's not right in this case! You shouldn't consider worlds of type f in your decision, because if you're in one of those worlds, your decision is pre-ordained. It doesn't make any sense to "choose" not to believe in free will - that belief may be correct, but if it is correct, then you can't choose it.

Over worlds of type F, the expected utility of B is FB x p(F), and the utility of b is Fb x p(F), and FB > Fb. So you always choose B.

Comment author: saturn 23 August 2009 06:27:29AM *  1 point [-]

The mistake you're making is that determinism does not mean your decisions are irrelevant. The universe doesn't swoop in and force you to decide a certain way even though you'd rather not. Determinism only means that your decisions, by being part of physical reality rather than existing outside it, result from the physical events that led to them. You aren't free to make events happen without a cause, but you can still look at evidence and come to correct conclusions.