On 4/28/2011 4:07 AM, Bruno Marchal wrote:
On 27 Apr 2011, at 22:48, meekerdb wrote:
On 4/27/2011 12:16 PM, Evgenii Rudnyi wrote:
Recently I have seen interpretation of quantum mechanics in terms of
quantum decoherence, for example Decoherence and the Transition from
Quantum to Classical by Wojciech H. Zurek. What is an attitude in
general to this? Is this good? Is there a good text for a layman
about such an approach?
There's a good review paper by Max Schlosshauer
He later expanded it into a book. Decoherence is a real, observed
physical process predicted by QM. Interest in it is due to it's role
in explaining the appearance of the classical world. It explains the
diagonalization of the reduced density matrix (the density matrix
after averaging over the unknown environment). But it doesn't
explain the realization of just one of the diagonal values with
probabilities according to the Born rule. Omnes and some others
point out that QM is a probabilistic theory and so probabilities are
all you can expect from it.
There is also a problem in explaining the basis in which the density
matrix is diagonalized; this is know as the einselection problem.
Decoherence theory suggests some possible solutions to the
einselection problem but none are really worked out yet.
Yes. Decoherence is real, and can be explained entirely in the QM
without collapse. It is a key ingredient of the Many-World
Interpretation, and that is why those who dislike the MWI try to still
add something to the decoherence effect. Basically decoherence comes
from the contagion of the superposition state to the environment,
which is a consequence of the linearity of tensor products and of the
linear wave equation.
I am not sure there is a "basis problem". Basis are selected by
universal-machine-tropic choice, and Zurek did provide explanation why
the position basis in favored by our type of branch. Quantum states
are relative states, and consciousness can find itself only on the
branches which support stable self-reflexive machine abilities.
I think more than "support" is needed - else you might find yourself the
the sole stable consciousness in a world full of quantum
superpositions. Steven Weinstein has shown this to be the generic case.
It is an open problem for me if other type of basis (than position)
can play that role.
Max Schlosshauer points out that small systems (e.g. atoms) are stable
in energy-momentum eigenstates, not position eigenstates.
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