From: scerir (scerir@libero.it)
Date: Thu Oct 03 2002 - 07:23:38 MDT
[me]
> ... impossible quantum retrodiction becomes
> perhaps a growing impediment.
[Rafal, long time ago]
> Do you mean the disappearance of the quasiclassical history at Planck
> scale (if this is the right expression)?
> If indeed this is the case, there would be a fundamental limit on our
> ability to discern the mutually exclusive histories of the early Universe
> before they decohered to produce our macroscopic world.
> The beginning would be then forever shrouded in mystery.
A corollary of the (quantum) no-cloning theorem, in the D'Ariano &
Yuen version, says that the 'knowledge' of the prior state of a single
quantum system violates the 'unitarity' of evolution
In other words we can also say (and there is also a theorem here)
that a quantum measurement is reversible iff no information
about the initial quantum state is obtained.
Now in the standard QM there are 'discrete' transformations which are
'unitary' (i.e. space reflections) and there are 'discrete' transformations
which are not 'unitary' (i.e. time reversal, which is 'anti-unitary'; that's
also why in QM time is not an operator, an observable, a dynamical
variable).
Unfortunately I do not know what happens at the Planck scale.
I mean I do not know whether, at the Planck scale, there are more
'unitary' than 'anti-unitary' discrete transformations, or whether there
are just 'unitary' or just 'anti-unitary' discrete transformations.
For a standard view about quantum retrodiction:
http://arxiv.org/abs/quant-ph/9501005
For a non-orthodox but consistent view:
http://arxiv.org/abs/quant-ph/9501002
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