Re: multiverse talk

From: Brent Meeker <>
Date: Mon, 07 Jul 2008 16:08:09 -0700

Ronald Held wrote:
> I am giving a talk on the Multiverse to Star Trek fans in several
> weeks. I would appreciate any advice and suggestions, since as of now,
> I have an outline based on Tegmark's four levels.
> >

One thing I would avoid is presenting the multiverse (of any level) as the
latest "gee-whiz, science has discovered that..." It is interesting
speculative metaphysics. Good fodder for SciFi fans but not yet science. I
cringe when Scientific American or the L.A. Times or some other popular
publication takes scientific speculation and hypes it as though it were a
new revelation of science. It happens most often in medical stories, but
also in physics and astronomy pieces. In the end I think it debases
science in the popular mind as just more advertising hype and spin noise.

ISTM there were several independent threads that lead to different ideas of
the multiverse:

1) The apparent inherent randomness of QM inconsistent with "hidden
variables" which made the "collapse of the wave function" mysterious and ad
hoc. The led Everett to argue for a relative-state interpretation which
implied the QM-multiverse. However, theories of einselection based on
decoherence and perhaps weak anthropic selection may undermine the
QM-multiverse. In this theory there is really only one universe but each
of us consists of multiple branches on which different values are projected.

2) Completely independent of (1), development of theories of cosmogony
based on quasi-classical quantum gravity showed the universe could arise
from "nothing". These theories naturally have the consequence that
arbitrarily many other universes could also have arisen. Any natural
process is repeatable. This theory of multiverses allows that universes
exist with different values of those physical constants that seem arbitrary
in our current theories (a set that could change). These universes all
exist in the same sense this universe exists, they may even have common
points (e.g. in singularities). Again some anthropic selection principle
must be invoke to explain *this* universe.

3) The extremely abstract nature of physics has led naturally to the
speculation that only the mathematics matters. We seem to know nothing
about elementary particles and the interior of black holes beyond the
mathematics they satisfy. So perhaps it is only the relational properties
of information coded into the mathematics that is the ur-stuff of the
world. In that case all possible information structures may be considered
equally "existent". This also fits with the idea that reality can be
simulated. If reality consists in the relation of information, it doesn't
matter how that information is embodied or maybe that it is embodied at
all. Therefore reality may *be* a simulation - as on the holodeck of the

4) Finally, what seems to have motivated Tegmark and also perhaps Bruno and
  others is Wheeler's question, "What makes them fly?" Why is one set
equations instantiated in the world and others are not? Why is there some
special property of "existing" that some possibilities have and others
don't. Tegmark sidesteps the question by answering that they are all
instantiated; so "to exist" is simply to be the subject of propositions
that form a non-self contradictory set. Starting from this he then must
try to recover some explanatory power by limiting what we experience by
appealing to some anthropic principle.

Brent Meeker

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Received on Mon Jul 07 2008 - 19:08:15 PDT

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