🚀 go-pugleaf

braham@physics.ubc.ca (Stephen Braham) writes:

>shouldn't be confused with the _dynamical_ collapse of the
>wavefunction, induced by decoherence processes- that's a statement
>on a Shroedinger picture density matrix, and ADH is a lot more
>general than that.
                                          ^^^^^^^^^^^^^^^^^^^^^^

Hmmmm... I have head it said that ADH may be too restrictive for any
system to match up to the Gell-Mann Hartle (GMH) criterion of quai-classical.
Even Omnes believes that the GMH decoherence criterion is too tough...
It must be checked in some actuall models.. Halliwell and Dowker 
(FERMILAB-PUB-92-44-A, CTP # 2071) have
ploughed through some awfull calculations for a very simple system of
a free particle coupled to a thermal bath (the Caldeira-Leggett model)
and have found that the histories do not decohere (ala ADH) completely
but to the extent that they do they seem to be peaked around the
classical paths in (x,p) phase space. But this is perhaps one of the
simplest models one can have and also there are still ambiguties
concerning how does one quantify how good the decoherence is, the
concept of peaking about the classical path, etc. How model dependent
are the results? Another model using ADH with inflation shows no
decoherence  whatsoever (in preperation). Harmonic oscillators, while
the testbed for many theories, possess many special properties not
found in even slightly more complicated models. 

Jason