On 12/4/2017 4:48 PM, Bruce Kellett wrote:
Do you not understand that one of the enduring mysteries of quantum theory is the emergence of the classical world from the purely quantum substrate? Decoherence goes a long way towards answering the underlying problems, but unless something intervenes to exactly zero the off-diagonal terms in the density matrix, the the understanding that we have is still only FAPP.
Yes, this is the interesting question. If the off diagonal terms, in some preferred basis, go exactly to zero, then Everett's multiple worlds is irrelevant. We only need to find that event which makes them zero...which is equivalent to collapse. Zurek purports to do this by saying that an immediate repetition of a measurement must produce the same eigenvalue. But that seems to me just another way of saying a measurement must collapse the wave function - except Zurek is attributing this zeroing of cross terms to the decoherence in the environment.
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