Recent paper on MWI

From: <>
Date: Thu, 29 Apr 1999 14:43:41 -0700

This is from

: Observational Consequences of Many-Worlds Quantum Theory
: Authors: Don N. Page (CIAR Cosmology Program, University of Alberta)
: Comments: 10 pages, no figures, LaTeX
: Report-no: Alberta-Thy-04-99
: Contrary to an oft-made claim, there are observational distinctions
: between "many-worlds" quantum theories, in which the quantum
: state "branches" without collapsing, and "single-history" quantum
: theories, in which something like a single macroscopic history
: occurs through some process such as the continual collapse or
: reduction of the quantum state. The observational distinctions
: occur as a result of processes in which observers are created
: or destroyed. One example is whether you may expect to observe
: anything within this universe after a time long compared with your
: life expectancy. Other examples are whether we would be expected
: to observe an expanding universe today in certain theories of
: quantum cosmology, or what value we might expect to observe for
: the cosmological constant.

Ah, yes, living forever as a consequence of the MWI, our favorite topic.
The paper discusses the (in)famous quantum suicide, following the
conventional reasoning that an observer in the MWI would always find
the suicide machine failing.

There is also some discussion of the role of measure in probability:

"Consider a theory of quantum cosmology that gives a quantum state for
the universe in which there are different 'worlds' with greatly different
numbers of observers. For calculating how typical various observations
are, in a single-history theory one should weight the 'worlds' purely by
how probable they are, but in a many-worlds theory, one should weight the
'worlds' not only by their quantum mechanical measures (the analogue in a
deterministic many-worlds theory of the probabilities in an indeterminstic
single-histories theory) but also by how much observation occurs with
each 'world'. This distinction leads to different predictions as to
which observations would be typical within the two types of theories."

He suggests that in MWI you should multiply the QM measure of a universe
times the number of observers to get an effective measure of the
likelihood of being an observer in that universe. This gives a boost to
universes with lots of observers and could conceivably make the universe
be big even in a cosmology where it was overwhelmingly likely to be small.
(Read it yourself to see what I mean.)

Received on Thu Apr 29 1999 - 14:50:53 PDT

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