From: scerir (scerir@libero.it)
Date: Mon Feb 24 2003 - 15:19:06 MST
>> The Wave Function: It or Bit?
>> Authors: H. D. Zeh
>> http://arxiv.org/abs/quant-ph/0204088
[Lee Corbin]
> "A state of incomplete knowledge is defined
> on a state of classical configurations?"
> What does that mean?
I don't remember what Zeh wrote in that paper.
Perhaps he was discussing the informational
completeness - no set of sharp observables can
be informationally complete (i.e. the Pauli
problem: under what conditions do position &
momentum distributions define a state uniquely?).
But we can say, in general, that the knowledge
of the prior state of a quantum system is impossible,
because, otherwise, the unitarity of the evolution
would be violated. This is sometimes called the
impossiblity of retrodiction. (There are quantum
interpretation, like the two-state time symmetrical
quantum description, shortly ABL rule, in which
retrodiction is not forbidden. What about MWI?).
D'Ariano and Yuen provided a general proof about the
impossibility of measuring perfectly the wavefunction
(or the density matrix) of a quantum system. Just
a reversible measurement does not violate the
unitarity of the evolution, but no information
about the prior state is obtained with a reversible
measurement.
>> This conceptual dilemma
> What dilemma?
"It" or "bit" I suppose. Reality or just information?
Why people say that a state is just information, but
a superposition of states is something physical?
Btw, something similar is going on about Bell inequalities.
The violation of inequalities is real?
That is to say: is there [1] a real effect (non-locality,
non-separability, etc.)?
Or is there some remarkable [2][3] conceptual error,
in the derivation of those inequalities?
(No one tested the original Bell inequalities! In performed
experiments *weaker* inequalities were violated).
[1] Is the moon there when nobody looks? D. Mermin,1985
http://digitalphysics.org/Publications/Mer85/scan.htm
[2] Betting on Bell http://arxiv.org/abs/quant-ph/0302113
[3] E.T. Jaynes, Clearing up Mysteries
http://bayes.wustl.edu/etj/articles/cmystery.pdf
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