Re: "Naive Realism" and QM

From: <kurtleegod.domain.name.hidden>
Date: Fri, 19 Aug 2005 10:25:51 -0400

 Serafino,

 I think I get the gist of what you are saying but it is not quite
 the case. There is no energy flux directly associated with
 wave-functions (like with electomagnetic or mechanical waves)
 but is a probability density and a probability flux associated with
 the square of linear functionals of the wave-function. The physical
 quantities (observables) pertaining to any physical system described
 by the WF typically do not have fixed values assigned by the theory
 but only "expectation values", i.e. probabilities of being found in
 one among many of their possible eigenvalues. Quantum Mechanics
 tells you how to compute these expectation values but only
 specific experiments assign one among them to a specific system.

 If I understand what you are trying to say below there is indeed
 a way of, a posteriori, trying to build a more or less classical
 picture of a propagation of a beam or even a single particle
 (represented by a wave packet or something like it).
 That is what is called a local hidden variable model for QM
 and it works fairly well for a single isolated degree of freedom.
 But, as it turns out, none of these clever "cartoons" can be
 used to fully interpret the quantum description; this is
 not merely the result of a theorem but something which has been
 verified empirically numerous times by now.

 Come to think of it, even my correction to Lee is in need of
 correction because QM is not just about amplitudes! The
 phase relations between wave functions play a very
 central role in the non local phenomena (i.e. Berry and
 Aharonov-Bohm effects) so the myth of "just amplitudes"
 should be dispelled by now.

 Best regards,
 Godfrey Kurtz
 (New Brunswick, NJ)

 -----Original Message-----
 From: scerir <scerir.domain.name.hidden>
 To: everything-list.domain.name.hidden
 Sent: Thu, 18 Aug 2005 22:55:51 +0200
 Subject: Re: "Naive Realism" and QM

 Godfrey:
> My point, if I can break it down a bit,
> is that the amplitudes correspond,
> not to "things" but to processes
> and that what the amplitudes let you
> compute are relative probabilities for
> the occurrences of such processes.

 Maybe. Amplitudes of (whatever) waves
 satisfy linear equations. So, amplitudes
 combine linearly when several paths are -
 in principle - possible. On the contrary,
 the intensity of waves, that is to say
 the energy flux, is quadratic in the field
 amplitudes. So, intensities do not combine
 linearly. If we imagine there is a relation
 between the energy flux and the number of
 particles crossing a given (unit) area (this
 can be the quantum principle, or the quantum
 postulate) we also imagine there is a relation
 between the energy flux - quadratic in the
 field amplitudes - and the probability for
 those particles crossing that (unit) area.
 We can also imagine now there is only one
 particle flying ....
 Regards,
 serafino



________________________________________________________________________
Check Out the new free AIM(R) Mail -- 2 GB of storage and
industry-leading spam and email virus protection.
Received on Fri Aug 19 2005 - 10:36:17 PDT