On Thu, Dec 10, 1998 at 03:20:58PM +0100, Gilles HENRI wrote:
> maybe the decision theory itself (I must confess that my only knowledge of
> it comes from what Wei writes here) is somewhat metaphysical because it
> assumes that an individual can actually change the evolution of the world
> ("acts upon it"). In any model (not only MWI) where human beings are
> nothing but rather complicated physical systems, free will is an illusion.
> They evolve simply (including in their "choices") following the physical
> laws. So you can theoretically determine what would be the "best" choice
> following some criteria, but you are never certain that a given physical
> system will follow this way. In MWI, you can also calculate a best way, but
> you are certain that other ways will be followed as well. In "one world
> interpretation", you can try to programm a system (or a brain") to maximise
> the probability of evolving along a "good" way, but I think it is also true
> in MWI (maximise the number of "worlds" where the "good" way is followed).

But in the MWI, you can't maximize anything since all of the measures are
predetermined by boundary conditions.

I agree the problem is with decision theory, and that's why I suggest we
find a new decision theory rather than reject the MWI. I think this is
serious and of interest to more than just economists, because decision
theory appears to be the only justification we have for Bayesian
probability theory. Probability theory was invented for gambling and its
axioms are still justified by showing that they lead (via decision theory)
to reasonable behavior. Without a viable decision theory, an MWIer would
have to either give up probability theory or accept it as a given without
justification. Then it won't even be clear what probabilities mean, since
they'll just be useless numbers.

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