On 10 Oct 2013, at 03:37, LizR wrote:
If Helsinki man understands the situation, he will assign a 100%
probability to him being duplicated and ending in both places.
Similarly a physicist who believes in MWI will assign a 100%
probability to him splitting and observing all possible outcomes.
This is not, however, how people normally view these matters. The
physicist feels that he had a (say) 50% chance of him observing spin-
up despite his knowledge of the MWI, and I guess Helsinki man feels
the same way about arriving in Moscow, if only because our brains
are "wired" to think in terms of the single universe view. I think
Bruno's take on this is acceptable in terms of how we think about
things in everyday life.
Once the duplication has been performed, one copy of the man then
has a 50% chance of being Moscow man, and his (spurious) sense of
always only being the single unique copy of himself would lead him
to feel that this was the chance beforehand. So it's fair for Bruno
to ask Helsinki man how he estimates his chances of arriving in
Moscow, assuming "folk psychology" is involved (ditto for the
physicist).
OK.
However this is only really quibbling about the fact that our
everyday attitude often doesn't cover the realities of how the
universe works.
The probabilities does not depend on how the universe work, but only
on computer science, which does not assume anything physical (note
even a physical reality).
Then the (easy) probability calculus we got here is part of the
explanation of how the universe works, and indeed why we are
confronted with an apparent universe/multiverses, although this is
part of the difficult remaining work (to get the correct hamiltonian
and things like that).
Bruno
http://iridia.ulb.ac.be/~marchal/
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