# Re: How does this probability thing work in MWI?

From: Jacques M. Mallah <jqm1584.domain.name.hidden>
Date: Wed, 24 Nov 1999 15:29:27 -0500 (EST)

On Wed, 17 Nov 1999, Fritz Griffith wrote:
> for every split in which we are favored to follow a certain world, there
> exists another world of equally real people who assumed they would follow
> the same path, who instead ended up in the so-called unlikely world.
> Because the people in both worlds are equally real, there is no way to say
> that we are more likely to follow either path; rather, between this
> single-split example, the chance would be 50/50 as to which world we would
> end up in. It would be arrogant to assume that we would have to be the
> people in the more probable world. Considering all possible worlds, we are
> back to the drawing board - the chance of us actually being in a world that
> isn't chaotic is pretty much nonexistant.
> Let me know if and why this doesn't make sense.

Hello. As you might have noticed, I am not like the other
posters to this list. Anyway, I'll have a go at answering your
question. First I'll refer to the MWI of QM.
You are correct to realize that the meaning of the probabilities
in the MWI, as usually stated, is far from clear. Usually it is handled
by attempting to show that the measure distribution, which is proportional
to the effective probabilities by definition, follows the usual rule for
the QM probabilities.
Well, if that is proven (and in fact it hasn't been), it does
solve that problem, but it is still unsatisfying if you feel, as I do,
that the effective probability of something should be proportional to the
*number* of something.
Enter my approach (stage right). I take a computationalist view,
in which the effective probability of a computation is proportional to the
number of "implementations" of that computation. That is, I use the SSA
as applied to implementations rather than "worlds".
Unfortunately that raises its own set of problems - "implementation"
is a concept I am still working on trying to define. I don't hide that
fact, but I think my web page (http://pages.nyu.edu/~jqm1584/cwia.htm)
makes a pretty good case for my approach.
The numbers in question are infinite but that is OK because the
ratio of two infinities is defined using a limiting proceedure.
OK, so much for QM. What people on this list have mostly been
talking about is the everything-hypothesis that all possible laws of
physics exist. Much of the debate centers on how to find out what a
typical observation would be like if that is the case, and on whether our
observations support that idea. I do not believe the everything-
hypothesis to be incompatible with my approach. In some ways, it may even
help solve the problems with it.
People have taken to calling the problem of simple laws the
"white rabbit" problem, so look for that in the archive as well as the
stuff about how the set of all possible Turing machine programs gives
an interesting measure distribution.
I hope this helps. My only request is that, when you understand
this stuff, you agree with me on the quantum immortality heresy :-)

- - - - - - -
Jacques Mallah (jqm1584.domain.name.hidden)