🚀 go-pugleaf

<MRG3@psuvm.psu.edu> writes:
> [some stuff deleted]

>A variation of this scheme included two density operators for both initial and
>final conditions. This seemed to be an attempt to remove the apparent
>introduction of time asymetry by hand. I hope the proposal has died a quiet and
>painless death. :)

HEY! <grin> It's quite a useful thing to do- it's more of an example
than anything though. The idea it to try to understand what we may
or may not get out of, say, a sum-over-histories, formulation of
quantum cosmology. There are ways of formulating the path integral
in such as way that you have, effectively, both past and future
conditions. You can simulate the effect in old-fashioned Hamiltonian
quantum mechanics by adding the final density matrix in. It IS useful
in certain circumstance, though. Tony leggett and others (including
my boss :)) have pointed out that you CAN do time-symmetric experiments
and you need this insertion of final conditions to get the right result.
In this situation, you have no density matrix at intermediate times
that can describe probabilities- you NEED the final condition part.
Tony's hoping to verify this with his squid experiments, of course.
Hmmmm, the reference part of this posting now has three members of
the same PhD graduating class in it <chuckle>. Go lions! <grin>

>-mike gallis
>mrg3@psuvm.psu.edu

			Steve

--
| Name: Stephen P. Braham | Perversion: Quantum Cosmologist|
| Hangout: UBC physics    | Signature:  Euclidean          |
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|          Canada         | E-mail: braham@physics.ubc.ca  |