Re: Are all QM interactions measurements?

From: Old Man (nomail_at_nomail.net)
Date: 10/19/04 

Date: Tue, 19 Oct 2004 14:18:59 -0500

"Simon Hopkins" <simon@hopkins9666.fsbusiness.co.uk> wrote in message
news:cl3815$81d$1@newsg1.svr.pol.co.uk...
> From my own point of view getting into philosophical arguments that can't
be
> tested experimentally is nonsense - this is really what Feynman was
talking
> about. Unfortunately, at the time it is not clear whether Feynman actually
> knew whether the double-slit experiments had actually been performed (in
his
> excellent books based upon his lecture course he refers to them only as
> thought experiments).
> Knowing when an object acts as a wave and particle is not a philosophical
> question but of great practical importance. How you interpret the results
of
> the Afshar experiment has profound implications. He assumes that you can
> actually refract probability wave functions - they do not collapse when
> they meet a lens.

This is a phenomenological interpretation, far removed
from metaphysics. Furthermore, Afshar didn't invent
it. It's old hat.

Under refraction, the time delay incurred in the effect
of photon absoption and subsequent emission can be
represented by a phenomenologically derived phase
shift in the incident wave function. This representation
is common in the analysis of nuclear particle scattering
experiments. It facillitates the quatitative comparison of
theoretical predictions to that measured.

> This implies that although steel walls collapse
> wavefunctions, glass lenses do not! This is a very important distinction.
I
> personally question the validity of the Ashfar experiment on this very
> basis. I don't think that any serious minded people actually subscribe to
> the Copenhagen interpretation nowadays but I wasn't really asking this
> question but the deeper question of how probability wave functions are
> affected by other objects.

It's phenomenological, it's quantitative, and it works, but
there's no metaphysics to be had from it. You can trust
the experiment and the quantitative analysis, but any piggy
backing metaphysics belongs in the trash bin.

[Old Man]

> Try this thought experiment. If you can't make sense of my description
> contact me directly for a .bmp file. Take a piece of paper and draw a
> diamond in the centre. The left and right points are convex lenses. The
top
> and bottom points are mirrors. If light comes from the left it is
refracted
> by the first lens. The refracted light is bounced from the mirrors to the
> lens on the right which condenses the light back parallel to that of the
> light entering the right lens. We take this system and place it in between
> the slits and the detectors in a simple double-slit experiment (slits on
> left). We position the lenses and mirrors close to the double slits such
> that there is not time for the two probability functions to interfere. If
> you can reflect the probability wavefunction then the two halves will
> interfere after the right lens. If the wavefunction collapses when it
meets
> the left lens then the photon can either go via the top or bottom
mirrors -
> we will see two clusters at the detector. Which result will actually
happen?
> I guess I could shut up but I still can't calculate ;-)
> Simon.
>
> "Old Man" <nomail@nomail.net> wrote in message
> news:sIadnRXwWLRzQencRVn-hQ@prairiewave.com...
> >
> > "Anthony Cerrato" <tcerrato@optonline.net> wrote in message
> > news:Fx2dd.10439$YM4.3872902@news4.srv.hcvlny.cv.net...
> > >
> > > "Old Man" <nomail@nomail.net> wrote in message
> > > news:Ju2dnZwPAvEGFencRVn-rw@prairiewave.com...
> > > >
> > > > "Anthony Cerrato" <tcerrato@optonline.net> wrote in
> > > message
> > > > news:klycd.28020$Fe6.12707137@news4.srv.hcvlny.cv.net...
> > > > >
> > > > > "Edward Green" <spamspamspam3@netzero.com> wrote in
> > > message
> > > > > news:eca320d0.0410161930.6052958e@posting.google.com...
> > > > > > "Simon Hopkins" <simon@hopkins9666.fsbusiness.co.uk>
> > > wrote
> > > > > in message news:<ckr3ui$dsh$1@newsg3.svr.pol.co.uk>...
> > > > > >
> > > > > > > I've recently read about a version of the
> > > double-slit
> > > > > experiment which uses
> > > > > > > lenses and mirrors
> > > > > > >
> > > > >
> > > (http://www.sciencefriday.com/images/shows/2004/073004/Afsha
> > > > > rExperimentSmall
> > > > > > > .jpg). I am a QM novice so my thinking may be wrong
> > > but
> > > > > I would have thought
> > > > > > > that when a photon meets a lens it collapses. A new
> > > > > photon is then created
> > > > > > > with a new wavefunction. Surely this means that
> > > Shahriar
> > > > > Afshar is not
> > > > > > > measuring wave-particle qualities of a single photon
> > > but
> > > > > wave like qualities
> > > > > > > of one photon and particle like qualities of
> > > another. Or
> > > > > am I deluding
> > > > > > > myself?
> > > > > >
> > > > > > I'm not only a perpetual novice, I'm an habitual
> > > > > deflationist: I fail
> > > > > > to see what is so wonderful about the results of this
> > > > > experiment.
> > > > > > Light is already "acting like a particle and a wave at
> > > the
> > > > > same time"
> > > > > > in any experiment involving wave interference and
> > > photon
> > > > > detectors:
> > > > > > nothing new has been added.
> > > > >
> > > > > The major point of the Afshar experiment is that he
> > > claims
> > > > > it disproves the principle of complementarity,
> > > formulated by
> > > > > Niels Bohr, which has been one of the cornerstones of
> > > > > Quantum Mechanics from the earliest days. The principle
> > > > > states that, either the particle-nature or the
> > > wave-nature
> > > > > of a fermion or boson (e.g., photon) may be determined
> > > in
> > > > > experiments, but not both at the same time. Afshar
> > > claims
> > > > > his experiment can detect both of these natures,
> > > throwing
> > > > > the Copenhagen Interpretation of QM into dispute.
> > > Whether or
> > > > > not his experiment is valid, is the question yet to be
> > > > > answered. ...tonyC
> > > >
> > > > There's nothing new under the Sun. Created as a
> > > particle,
> > > > the photon suffers self-interference as a wave, and is
> > > finally
> > > > absorbed and detected as a particle.
> > > >
> > > > It's all metaphysical smoke and mirrors; verbal
> > > slights-of-
> > > > hand; falsification of unlivable straw men. Quantitative
> > > > prediction is all that counts. As Feynman said, shut-up
> > > and
> > > > calculate !
> > > >
> > > > [Old Man]
> > >
> > > Are you saying that Afshar's claim that the principle of
> > > complementarity, which has been a cornerstone of Quantum
> > > Mechanics from the earliest days, is wrong? If you are, come
> > > right out and say it--and justify it with physics, not
> > > semantics.
> > >
> > > I've been hearing that "shut-up and calculate!" crap for
> > > decades, and that's why there's been absolutely no real
> > > progress on _understanding_ QM on any fundamental level
> > > since Bohr et al. devised the Copenhagen Interpretation.
> > > There are only 2 possibilities, Afshar's statement is right
> > > or it is wrong. If you don't know, say so, and let others
> > > get on the pot to figure it out. If you do know, please
> > > explain a little more clearly. What exactly is the straw man
> > > here? Regards, ...tonyC
> >
> > Old Man wonders where Cerrato got the audacious notion
> > that wave and particle represent mutually exclusive modes.
> > Certainly not from Bohr. Possibly from Afshar ?
> >
> > [Old Man]

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