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

From: Fritz Griffith <fritzgriffith.domain.name.hidden>
Date: Mon, 22 Nov 1999 18:01:13 MST

ok, I understand that QM defines the probability of which universe we will
end up in. That's not the problem. The problem only occurs when you
consider the fact that in some cases, a world with SAS's will split into
more than one world with SAS's. The SAS's in the original world could
determine a probability between two different worlds being theirs. Perhaps
one world has a 90% probability and the other has a 10% probability. But
regardless of the probability, when the world does split, there will be
SAS's in the likely world, and SAS's in the unlikely one. For the SAS's
that end up in the likely universe, everything is good. Unfortunately, for
every world that was expected to happen, there will be AT LEAST AS MANY
WORLDS THAT WERE UNEXPECTED BUT DID HAPPEN, observed as a whole by the SAS's
of all universes. So, no matter what kind of reasoning you apply to QM
probabilities, the unexpected will happen to all but a very small minority
of SAS's. How can we be so lucky as to be among that small minority?

>From: juergen.domain.name.hidden (Juergen Schmidhuber)
>To: fritzgriffith.domain.name.hidden
>CC: everything-list.domain.name.hidden
>Subject: Re: How does this probability thing work in MWI?
>Date: Mon, 22 Nov 1999 10:03:44 +0100
>
> >So what about the continuations corresponding to the longer algorithms?
> >Those worlds still exist, don't they? If so, then for every shorter
> >algorithm, there are continuations of longer algorithms, which were
> >identical up to that point, but which now represent worlds which don't
> >follow the laws of QM, but in which people neverthless still live in.
>You
> >can say that the universal prior determines that I will probably follow a
> >short algorithm, but what can you possibly say about all those people in
>all
> >those worlds who didn't follow the shortest algorithm? Unless there are
> >less worlds like theirs than like ours, I just can't see how you can
>dismiss
> >their worlds as less probable.
>
>Continuations corresponding to longer algorithms also get computed, of
>course. But they are less probable indeed. According to the universal
>prior the probability of an algorithm is the probability of successively
>guessing each of its bits. The longer the algorithm, the smaller its
>probability.
>
>I believe this simple and in hindsight obvious line of reasoning
>was absent in previous MWI discussions. The UTM theory of everything
>provides a novel explanation that seems more convincing than the