From: paul@mtnmath.UUCP (Paul Budnik)
Newsgroups: sci.physics
Subject: Re: Budnik's proposed experiment (was Re: temporally undecided states)
Date: 4 Jan 93 17:24:35 GMT
Organization: Mountain Math Software, P. O. Box 2124, Saratoga. CA 95070

In article <1993Jan4.000908.2023@cs.wayne.edu>, atems@igor.physics.wayne.edu (Dale Atems) writes:
> [...] 
> Okay, the unfamiliar element to me here is the changing of the
> polarizer angles while the wave function is passing through, thereby
> changing the quantum state after the photons have been emitted. As I
> said, I've lost touch with this field. Any references you can give to
> help me out?

Aspect's experiment changed the polarizer angles while the photons were in
flight. The problem with that experiment was that Aspect did not directly
measure the delays, but estimated them based on the distances and presumed
flight times of the particles. These classical assumptions are not in
general valid in QM. References:
Aspect, J. Dalibard and G. Roger, Physical Review Letters Vol 49,
pg. 1804 (1982)
J. D. Franson, Physical Review D, pgs. 2529-2532, Vol. 31, No. 10, May 1985

> >Well QM does not predict these delays it puts constraints on them.
> >Thus it still predicts that locality is violated. If these delays turn
> >out to be consistent with locality, as I expect they will be, then QM is
> >not just incomplete, it is false. 
> 
> To comment intelligently on this I would have to know exactly how you
> are defining locality operationally -- this seems to be hidden inside
> the details of the statistical analysis you are performing to estimate
> the time at which the probability of joint detections changes.

Its not my definition and its not original. The simplest notion of locality
involves a single cause and effect. Tests of Bell's inequality are
complicated because there are two `causes' and two `effects'.


    |---------\---------------[ ]--------------------/--------|
Detector   Polarizer      Photon source            Polarizer    Detector
  D1         P1                                       P2          D2
      Site 1                                             Site 2

The experiment is done in an inertial frame of reference. We simultaneously
change the two polarizer angles and ask how long it takes for this to
affect the probability of joint detections. This time must be short enough
so that light could not travel from either P1 to D2 or P2 to D1 in this
time if we are to show locality is violated.

If you want an analysis of how one proves locality is violated
in such an experiment see: "Bell's Theorem and the Different Concepts of
Locality", P. H. Eberhard, Il Nuovo Cimento 46 B, p 392, (1978).

There is noting special about the statistical analysis I am describing.
Quantum mechanics only predicts the probability of joint detections so
we need a statistical analysis to estimate when the probability changed.
We need many trials to get an accurate estimate. In addition we have
no control over when photons are emitted. Thus there will be some
element of the delay the comes from lack of synchronization between
when the photons traverse the polarizers and when the polarizers change
angles. We need to minimize this affect by emitting photons at a high
rate and minimize the residual effect by statistical analysis.

> Still if QM does set the constraints you say, then the experiment is
> worth doing. My question would be: why do you expect that locality, as
> you define it, will be upheld?

I think it is the opposite question that should be asked. Consider
a singlet state photon pair that was emitted from a distant galaxy.
The photon paired with this has been traveling in the opposite
direction for billions of years. QM predicts that these two are
still connected. If you detect one photon in this pair by looking at
the night sky with polarizing sun glasses you will instantly impose
a constraint on the polarization of the other photon billions of light
years away according to existing theory. To me such a prediction
requires extraordinary justification.

Such extraordinary justification does not exist. There is
*no justification at all* for this preposterous prediction. There is
not a shred of evidence that there are macroscopic violations of locality
in nature. The only part of QM that predicts this is the assumption that
the wave function changes instantaneously when an observation is made.
This in turn is a completely arbitrary assumption without a shred of
experimental evidence to support it.  We say in computer science
`garbage in, garbage out'. In physics we start with an arbitrary
unjustified nonlocal assumption and we get a nonlocal theory.
Surprise, surprise! Why should anyone believe such a theory is correct? 

> >However, it is only one aspect of QM
> >that is tested by measuring these delays: the assumption that the wave
> >function changes instantaneously when a measurement is made.
> 
> What do "quantum eraser" experiments tell us about this assumption? I
> was under the impression from someone's recent post that some
> experimental work on this had already been done.

There is a fair amount of experimental work in this area. To my knowledge
none of it has addressed the issue of directly measuring the delays needed
to prove locality is violated. There are nonintuitive and interresting
effects in this area. There is no evidence yet that any of these effects
violate locality.
>
>[...] 
> >On the other hand, if these delays are consistent with
> >locality these experiments will open a window on an entirely new class
> >of physical phenomena. If the wave function does not change instantaneously
> >then it undergoes some nonlinear structural change that is completely
> >outside of any existing theory. Understanding the structure of these
> >changes could be as important as QM itself. Bell's inequality may open
> >an experimental window on a new class of physical phenomena.
> 
> At the moment, of course, this is pure speculation.

I think it is a lot less speculative then the prediction that looking at
the night sky with polarizing sunglasses affects instantaneously what
happens billions of light years away.

Paul Budnik