On 05 May 2016, at 22:40, Brent Meeker wrote:
On 5/5/2016 5:57 AM, Bruno Marchal wrote:
I will at the positive aspect. You seem to agree with the
computationalist FPI. That is a progress. Now just reread Everett.
Pure state evolves in pure state, and never becomes mixture in the
MW. The third person view is given by the wave or matric formalism.
The relative state are given by partial trace. We can define a
world by a set of things close for interaction, this automatically
ensure locality.
But the partial trace is not a physical process, it's choice of the
analyst. Although decoherence provides some guidance it doesn't
completely solve the Heisenberg cut problem. And even after taking
the partial trace and getting a reduced, diagonal density matrix
there is no physical principle for saying which are realized and why
the trace in that basis instead of another.
I think that the FPI is enough. The partial trace is not physical, but
its phenomenology is real and dictated by the choice of the measuring
apparatus. It would be physically real, like with the collapse, then
we would have action at a distance.
Roland Omnes looks at this analysis and says, "QM is a probabilistic
theory. So when it predicts probabilities that all you can expect."
One of its book is the most brilliant defense of the MWI, but in the
last paragraph of the book, he admit hating that idea, and decide that
it was time to be irrational and decide that some God selects one
physical reality.
Bruno
Brent
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