Re: Which is Fundamental?

From: Hal Finney <hal.domain.name.hidden>
Date: Tue, 10 May 2005 13:16:08 -0700 (PDT)

Lee Corbin writes:
> Why not instead adopt the scientific model? That is, that
> we are three-dimensional creatures ensconced in a world
> governed by the laws of physics, or, what I'll call the
> "atoms and processes" model. About observer-moments, I would
> say what LaPlace answered to Napoleon about a deity:
> "I have no need of that hypothesis".

Observer moments are more than a hypothesis, they are our raw experiences
of the world. It is more the world that is the hypothesis to explain
the observer moments, than vice versa. "I think, therefore I am... an
observer moment," as Descartes meant to say.

However, given the strong evidence we have for the world's existence and
the explanatory power it gives for our experience, I don't think there
is a problem with treating it as fundamental. This leads to a model of
world -> observers -> observer-moments. A world maintains and holds
one or more observers, which can themselves be thought of as composed
of multiple observer moments.

A key point is that the mapping is not just one-to-many. It is
many-to-many. That is, an observer moment is shared among multiple
observers; and an observer exists in multiple worlds.

To explain the first point, observers merge whenever information is
forgotten. And they diverge whenever information is learned. This means
that each observer-moment is a nexus of intersection of many observers.
The observer moment has multiple pasts and multiple futures.

To explain the second point, observers exist in any world which is
consistent with their observations. The amount of information in
an observer is much less than the amount of information in a world
(at least, for observers and worlds like our own). So there are many
worlds which are consistent with the information in an observer, and
the observer can be thought of as occupying all of those worlds.

In this sense, the mapping above might be better expressed as world <->
observers <-> observer-moments. It is many-to-many in both directions.

I see both views - worlds as primary, or observers and observer-moments as
primary - as playing an important role in understanding our relationship
to the multiverse. In terms of choosing actions or making predictions,
we need methods for making quantitative estimates of what is likely
to happen. This requires us to take into consideration the set of
worlds which our observer-moments span, and the set of possible future
observer-moments which we care about.

To calculate, we need a measure over observer-moments. Then we can have a
greater expectation of experiencing observer moments with higher measures.
So how do we do this calculation?

I start by calculating the measure of universes. Using an arbitrary,
simple, universal computer, I would calculate the minimum program size
for creating a given universe. (Yes, I know this is non-computable, but
we can approximate it and use that for our estimates.) The program size
gives the measure of that universe, and then that measure should lead
us to a measure for the observers and observer-moments in that universe.

This step of going from universe-measure to observer-measure seems a bit
problematic to me and I don't have a completely satisfactory solution,
but I won't go into the details of the problems right now.

Anyway, once you have the measure for an observer moment in a given
universe, you can sum the measures over all universes that generate that
particular observer moment, to get the measure of the observer moment.

Then, with a measure over observer-moments, you can take your current
observer moment, look at ones that you identify with in the future, and
consider the measure of those observer moments in helping you to choose
what actions to take. This is how one should behave in a multiverse.

This approach seems to require acknowledgement of the fundamental
importance both of worlds and observer-moments. We use worlds to
calculate measure; we use observer-moments to constrain the set of worlds
that we occupy, now and in the future. A world-only approach would seem
to pin us to a single world and not recognize that we span all worlds
which contain identical observer-moments; an observer-only approach does
not seem to give us grounds to estimate measure a priori (although I
think Bruno may have a method which is supposed to do that). We have
to use both concepts to get a complete picture of what is going on.

Hal Finney
Received on Tue May 10 2005 - 16:22:55 PDT