Re: Cardinality of the MW

From: Gilles HENRI <Gilles.Henri.domain.name.hidden>
Date: Tue, 20 Jul 1999 12:10:51 +0200

Hi everybody!

I've been very busy these days and not able to follow the recent
discussions on the list. And woow! there seems to be a lot to catch up!
Rather than trying to recapitulate all past universes I just try to
immiscate in the present discussion.
It seems that again the difficult point is how to define identity, i.e.
what allows to gather a number of different subsystems into the same "I"?
I already expressed my point of view that this can not be done in an
absolute way in MWI. Unlike most of you, I don't think that we can be
defined or assimilated to some computation. So the meaning of "other
implementations of me" is not obvious at all. I think that the identity is
meaningful only in a classical spatio-temporal frame, which is
approximately realized through "classical histories" of MWI. In these
classical universes (subparts of the "big" Universe), we can follow
continuously a macroscopic system (such as "us", but also any other
"object" or "being"), which IMPLIES a continuous function of space and time
(although allowing some branching events during quantum measurements) . Out
of this frame, identity is meaningless.

>> > > >
>> > > > But if you believe in the computationalist hypothesis, then you'd
>> > > > have to assume that at some point, a simulation of a human becomes
>> > > > "close enough" to be identical. That is (to oversimplify) when
>> > > > each particle is simulated to within a Plank length, then the
>> > > > simulation becomes indiscernable from the original, and thus
>> > > > identical. If this is true, then I would no longer expect the
>> > > > physical laws to give rise to ever-increasing cardinality of
>> > > > universes, since that could never increase the cardinality of
>> > > > the set of humans past aleph-0, anyway.

Again it seems that i am one of the few not believing in this possibility!
I summerize my objections for the new contributors:

Objection 1 : unlike what some of you seem to believe, QM forbids the
measurement of a quantum state, because the (complex) value psi(x,t) does
not correspond itself to an observable. We can only check statistically the
prediction of QM concerning measurements of classical quantities x, p, E,
but not measure a particular quantum state (including ours)...

 Objection 2 : even if the world were classical (which it is not of course)
we are constantly interacting with our environment. The simulation of a
complete Universe with a machine embedded in this very Universe (so
including the machine itself) is impossible. So an "exact" simulation,
leading to exactly the same evolution, is physically impossible.

Objection 3 (maybe the worst) : we do not have a finite description of the
physical reality that would allow to "describe " it exactly (nothing to say
of predicting its evolution). Even Wheeler DeWitt equation, superstring
theory and so on are at best putative hypothesis that could possibly answer
some problems raised by quantum field theory, but nobody can claim that
they are "THE" ultimate TOE. "Simulating each particle to within a Plank
length" is also meaningless for the moment, since the Planck length is just
the scale at which we do not know how to simulate anything...

 Up to now, physics has only offered approximate descriptions of reality
which tend to describe better and better the observations. That's all and
that is already something! forget about ontology...

Gilles
Received on Tue Jul 20 1999 - 03:16:18 PDT