Re: relevance of the real measure

From: Wei Dai <weidai.domain.name.hidden>
Date: Fri, 21 Dec 2001 14:53:31 -0800

On Fri, Dec 21, 2001 at 12:12:41AM -0800, hal.domain.name.hidden wrote:
> Measure is not supposed to be just an abstract number that is attached
> to a universe. It has meaning in terms of our own perceptions and
> experience in that universe. The all-universe theory includes both a
> model of universes which exist, and a way of relating our experiences of
> consciousness to those universes. In the theory, if there is a physical
> system in the multiverse which is isomorphic to our own mental state, then
> the probability of experiencing subjective consequences which correspond
> to changes in that system will be proportional to its measure.

This may be true but I don't think utility functions should be based on
subjective experiences. Otherwise everyone would endlessly re-run
simulations of their most favorable subjective experiences. Utility
functions should be based on external reality, so you'd choose actions
based on their overall effects on the multiverse. In that case it's not
clear why we should care about each universe in proportion to its measure.

This may make more practical sense if you consider the debate between
Juergen and I about Speed vs. more dominant priors. Even if I believed
that the multiverse was instantiated by a Great Programmer running the
FAST algorithm, why should I then care about each universe in proportion
to its Speed prior instead of any other arbitrary measure that I choose?

> Think of a single-universe model with ordinary probability, where you
> have a bet with a 90% chance of outcome A and 10% chance of outcome B.
> Conventionally you should take the bet which maximizes your expectations
> based on A occuring. But you could imagine someone who only cared about
> what happened if outcome B happened, and bet on B so that he would do
> well in that unlikely case. It's rational in a certain sense, but it
> is going to lead to bad consequences in practice.

I think there is a significant difference in that in the single-universe
model someone like that wouldn't survive very long and therefore evolution
would eliminate this kind of utility functions. But in the multiverse
model, this person would continue to survive in the universes that he
cares about and actually he would do very well in those universes, whereas
you would do poorly in those universes but do well in the universes you
cared more about. So there is a symmetry between him and you that doesn't
exist in the single-universe model.
Received on Fri Dec 21 2001 - 14:55:24 PST