From: scerir (scerir@libero.it)
Date: Fri Feb 14 2003 - 16:52:11 MST
[Damien]
> > But wait! Here's this great swathe of possible paths, all of them
> > taken, each of them the trajectory native to its own idiosyncratic
> > world--but what *we* *here* experience is (almost) always that one
> > goddam minimal action path. This looks wildly inconsistent with MW to
> > me. (Of course it might be that in the MW manifold there is an a
> > priori high p value for the least action path, so any observer is
> > almost always in such a world--but that just establishes by fiat what
> > is meant to be explained.
> > Any takers?
[Rafal]
> Let me guess: the measure of universes close to the minimal action path
> is much greater than the measure of universes diverging from it
> significantly?
> There is a Damien who always wins the lottery :-)
Griffiths and, later, Gell-Mann & Hartle realized that it was possible
to build an ontology, well maybe a ... cosmology on Feynman's
representation. And they called it *consistent histories*.
The main principle of Griffiths' theory is this. If a quantum system
has a certain value after a measurement, it had it shortly before the
measurement,and it will keep it shortly after the measurement. The
theory supposes established the initial and the final events,
independently from whatever happened and from whatever will happen.
Shortly the *consistent* condition means that the effects of
interference are negligible. And this means that there is no
interference in quantum amplitudes propagating from an event to
another event (in the Hilbert space) along *separate* paths.
If (and only if) the particular history is consistent it is
also possible to attach a weight, or, let us say, to calculate
a probability for that individual history.
Gell-Mann & Hartle were the first top physicists who realized that
decoherence was the missing point in Griffiths'consistent histories.
A history (which here may be fine-grained or coarse-grained) is a
particular sequence of alternatives. It is possible to have histories
within histories, depending on the fine- or coarse- graining.
Feynman liked so much this approach, also because its formalism
is based on an application of Feynman's path integral representation.
So, yes, Damien wins often the lottery if he focused and .. lucky.
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