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).


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).



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