Decision theory

From: Jacques M Mallah <>
Date: Thu, 24 Dec 1998 17:22:13 -0500

On Thu, 10 Dec 1998, Gilles HENRI wrote:
> >On Wed, Dec 09, 1998 at 08:12:38PM -0500, Jacques M. Mallah wrote:
> >> On the contrary, it's the same. That is easy to prove: suppose
> >> the MWI was false but assume the universe is spacially infinite, so there
> >> are other people like you in distant galaxies. Clearly they have no
> >> bearing on what you do, so you should make the usual decisions, including
> >> of course any suicide decisions. It is no different in the MWI; the only
> >> difference is that the others are in different parts of wavefunction
> >> configuration space, rather than regular space.
> >
> >Unfortunately because currently accepted decision theory makes some
> >metaphysical assumptions, it can be compatible with a spacially infinite
> >universe but not with MWI. Basicly decision theory depends on the idea of
> >alternate realities and the notion that an individual chooses the actual
> >reality among the alternatives as he makes decisions and acts upon them.
> >But according to MWI, all alternatives are real and have predetermined
> >measures.
> >
> >I can't figure out how to apply decision theory with the MWI. If you can,
> >show us how, and please include an example.
> 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).

        In this case, Gilles has it right. Wei, the problem you mentioned
is seperate from the MWI, and I don't think it's really a problem at all.
It's that there is no such thing as free will. In fact, the whole concept
of free will never made any sense. The only possibilities are determinism
and randomness, neither of which allows any 'decisions'.
        But as Gilles said, some choices are better than others. This is
no paradox; it's just a different way of describing the same thing. At
one level of description I can describe a process as a physical system
evolving in time according to the laws of mechanics; at another level, I
can describe it as a computer, following a certain algorithm, without
getting into physical details; at another level, I can describe it as a
person making a decision, without getting into algorithmic details.
        So the real question is what reasoning should we use to make that
decision. It is true that our decision may be predetermined, but that's
besides the point; our reasoning is not supposed to replace the laws of
physics, it *is* the laws of physics in action. Us 'acting as though we
have free will' is what the way the laws of physics make us do. And the
correct decision is still the one that maximizes the things the laws of
physics make us think we want.
        It's just the same way a computer uses if..then statements to make
decisions, while at the same time the course of the program is
predetermined. It's choosing from two alternatives in the sense that if
the program were changed, the outcome would change too.

                         - - - - - - -
              Jacques Mallah (
       Graduate Student / Many Worlder / Devil's Advocate
"I know what no one else knows" - 'Runaway Train', Soul Asylum
            My URL:
Received on Thu Dec 24 1998 - 14:23:41 PST

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