Re: Everett

Nicholas Bostrom (
Thu, 31 Jul 1997 16:50:20 +0000

John K Clark <> wrote:

> In 1957 Hugh Everett solved the measurement problem but at a very high price,
> too high most thought. He said that when any particle undergoes the smallest
> detectable change ( a quantum jump ) the entire universe, including you the
> observer, duplicates itself and splits in two, but we have (almost) no way
> of communicating with the other universe. If true this would mean there is an
> infinite number (some say just an astronomical number) of universes.

Apart from the staggering ontological implications, there is one
objection that many philosophers of physics consider fatal: The
Everett theory fails to make sense of the probabilities. For
instance, take a particle that can undergo either of two processes,
and say that according to quantum mechanics the first event (A) has
an 80% chance of occuring, and the second (B) 20%. Now, according to
the Everett interpretation what happens (basically) is that the
universe splits into two universes; and there is one copy of me in
each of these universes. But if this were the case, then there should
be a 50% chance for me (i.e. *this* copy of Nicholas Bostrom) to
find that A had happened and a 50% chance that B had happened; which
we know from experiment is not true.

I don't know of any good reply to this objection that would save the
Everett interpretation.

P.S. A serious but very reader-friendly introduction to the
philosophy of quantum mechanics is David Albert's Quantum Mechanics
and Experience (1992).

Nicholas Bostrom

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