Re: locality and nonlocality

From vjs@uhheph.phys.hawaii.eduSat Oct 21 01:20:32 1995
Date: Fri, 20 Oct 1995 23:42:46 -0700
From: Vic Stenger 
Reply to: quantum-d@teleport.com
To: subscribers of list 
Subject: QUANTUM-D: RE: locality and nonlocality

Notice how often, in Rhett's discussion below, he uses the term
"pre-existing."  He is forcing a macroscopic prejudice on the quantum
system. I claim that you can get rid of nonlocality and the other paradoxes
of QM by allowing time to flow either way at the quantum level--as it in
fact is allowed to do when you work with fundamental processes in Feynman
diagrams. 

This is what Cramer does in the Transactional Interpretation, but I do 
not think it is necessary to introduce his "offer" and "confirmation" waves.
Just let particle turn around and go backward in time.

In the double slit, for example, an electron or photon goes through one 
slit to the detector, then back in time through the other slit to the 
source, and around and around.  Thus it passes simultaneously through 
both slits and a seemingly spacelike correlation exists, but it is local 
since the particle never travels faster than light.

The Bohm-Bell-Aspect-EPR experiment can be viewed in a similar way.
In the time-reversed view, positrons are emitted from the detectors which 
travel to the source.  Those that are triplets are tossed out 
locally, leaving the singlets.

On general, QM is contextual.  You must know the experimental 
configuration.  Change it, and you get different results.  This is viewed 
as spooky in the normal uni-directional time perspective, because you can 
change the final detector arrangement around after the particles have 
left the source.  But in a time-reversed view, you made the change earlier, 
so nothing spooky happened.

Note I do not demand complete time-reversal symmetry, just time reversal. 
Since uni-directional time is a macroscopic, many-particle convention, it 
does not apply at the quantum level.

I have written about this and much else in my book _The Unconscious 
Quantum: Metaphysics in Modern Physics and Cosmology_ to appear next 
month from Prometheus Books.  I am currently working on an article 
entitled "Viewing Quantum Mechanics from a Time-Reversible Perspective" 
that I plan to sent to Am J. Phys.  If anyone would like to help me by 
commenting on the latter (too late now for the book), please let me know 
and I will email the article, or send you a postscript file if you like.

Mitch will remember an earlier discussion on this that did not convince him.
************************************************************************
Victor J. Stenger
Professor of Physics
Department of Physics and Astronomy                 Phone: (808)956-2942
2505 Correa Road                                      Fax: (808)956-2930
University of Hawaii at Manoa                 vjs@uhheph.phys.hawaii.edu
Honolulu, HI 96822
************************************************************************
   

On Wed, 18 Oct 1995, Rhett Savage wrote:

> Mitchell Porter posted a beautiful comment by Gerard 't Hooft which 
> mentioned the possibility of explaining the violations of the Bell 
> inequalities and related results using purely local causes. I don't 
> think that the proposed solution works, for the kind of conspiracy 
> that 't Hooft invokes is bizarre! Let me briefly review the problem 
> which 't Hooft is trying to solve...
> 
> I. Entangled states
> 
> In 1935 Einstein and two of his students Podolsky and Rosen brought 
> attention to multi-particle quantum systems. We can gain information 
> about one of a pair of particles without going anywhere near it, by 
> measuring the other particle; in a real sense we are indirectly yet
> definitively measuring the particle at a distance. E, P and R viewed 
> this as a clear indication that what measurement does is to uncover 
> pre-existing facts - the alternative is that measurements may effect 
> changes at a distance, instantaneously!
> 
> Of course, 29 years later in 1964 John Bell showed that some sort of
> nonlocal effect must be occurring - according to a rigorous analysis, 
> local facts could not through any possible cleverness be arranged so
> as to be prepared, at one and the same time, to answer every possible 
> consistency question which we might pose to the whole system. 
>  
> In other words, pre-existing localized facts are formally incapable of 
> generating run-of-the-mill quantum correlations.
> 
> II. Bell's theorem
> 
> Bell considered the various possible measurements on one particle of 
> a multi-particle state: we might measure 'this' (eg. polarizer angle) 
> or 'that,' depending on our whim.
> 
> Meanwhile, our  choice of measurement results in our obtaining various 
> kinds of information about other, distant parts of the system. To the
> extent that we believe in the locality of influence it seems that we 
> imagine that throughout the system are pre-existing "facts," ready to 
> swim to the surface, corresponding to each possible question we might
> pose... 
> 
> On a given run of the experiment an outcome happens and we might say
> that some set of pre-existing facts underlay that; then it turns out 
> that this particular set of "facts" would have given a different (in 
> fact less correlated) outcome than quantum theory if we had measured
> something else. No matter how we seek we cannot find any local set of
> facts which would give consistent answers to all possible choices of 
> measurement.
> 
> Modern versions of Bell's theorem, such as those due to Greenburger,
> Horne, and Zeilinger (GHZ) show bluntly that no set could behave in 
> the right way for every possible measurement. 
> 
> Thus, correlation in quantum systems does not seem to be a matter of  
> pre-existing facts after all; the world must really be making it up 
> as it goes along. Local properties of quantum systems emerge "all at 
> once," and often at a distance. Quantum wavefunctions collapse at a
> distance as surely as they do so locally. 
> 
> III. Nonlocality
> 
> An even sharper formulation of nonlocality is possible...
> 
> Quantum nonlocality is *this* tangible: what is measured in one place 
> leads to different outcomes in other, nonlocally distant places than 
> would otherwise have happened. 
> 
> Henry Stapp formulated the result in 1977 as follows: 
> 
>   "What happens macroscopically in one space-time region must 
>    in some cases depend on variables that are controlled in 
>    far-away, space-like separated regions... [ie.], there is 
>    no way within the set of all conceivable combinations of 
>    conceivable results for the results in each region to be 
>    independent of the choice made in the other region."
> 
> IV. Locality regained?
> 
> Of course, there are many excellent reasons that physicists mistrust 
> and even actively dislike nonlocal connections - what room remains to 
> wriggle here? 
> 
> Into the fray leaps 't Hooft...
> 
> On Thu, 28 Sep 1995 Mitch Porter wrote:
> 
> > A remark from Gerard 't Hooft, which can be found in _Physics and our
> > view of the world_, ed. Jan Hilgevoord (Cambridge U.P., 1994), p28:
> > 
> > In my opinion (but I stress that this is a minority view), there
> > may nevertheless be a compromise [between locality and Bell's
> > theorem]. This is that there is no direct action at a distance,
> > but there is some sort of "conspiracy". With this I mean that the 
> > "state" of Nature that we now call "vacuum" is actually a very
> > complicated dynamical solution of the equations of motion, 
> > showing correlations over space-like distances. Einstein, Rosen,
> > Podolsky and Bell never took such correlations completely
> > into account. With correlations we can have apparently impossible
> > "coincidences" spreading faster than the speed of light, but which
> > are not in conflict with the requirement of special relativity
> > that information cannot spread faster than the speed of light.
> > 
> 
> Let us mark clearly the nature of this "conspiracy" - 't Hooft must 
> be suggesting a complete abandonment of free-will even in its most 
> general form.
> 
> Isn't he imagining an orderly, local universe where apparent nonlocal 
> patterns are the result of one pre-determined pattern being laid atop 
> of another? 
> 
> And one of these patterns is the sequence of polarizer angles chosen 
> at either end of an EPR apparatus...!
> 
> The formal aspect of Bell's argument which 't Hooft questions is the 
> contemplation of different possible measurements, with the discovery 
> that no set of localized facts could be ready for them all - if there 
> are not many possible measurements, if the world knows ahead of time 
> just what polarization angles will be compared, then the cosmic deck 
> could easily be stacked with local variables so as to act apparently 
> consistently, even at a distance.
> 
> What is distinctive about 't Hooft's comments is the ease with which 
> he locates the conspiratorial mechanism:
> 
> > the "state" of Nature that we now call "vacuum" is actually a very
> > complicated dynamical solution of the equations of motion, 
> > showing correlations over space-like distances... 
> 
> A very lovely thought, and no doubt true; but can this be considered 
> to be a suitable exorcism of nonlocality as t'Hooft offered it? He
> said that 
> 
> >                                            Einstein, Rosen,
> > Podolsky and Bell never took such correlations completely
> > into account. With correlations we can have apparently 
> > impossible "coincidences" spreading faster than the speed 
> > of light...
> 
> Yet the correlations that he is referring to include my choice of what
> to measure - Is my choice really fixed by the underlying equations of 
> motion, in just the right way as to ensure consistency in the particle 
> experiment? 
> 
> How could it be!?
> 
> What if my choice *is* fixed (and this is how the world plays quantum 
> theory, with a stacked local deck) and then i begin to base my choice 
> on the swishing of a cat's tail? (When she swishes one way i rotate a 
> polarizer thusly, and vice versa.) Would such swishes of the tail now 
> be locally fixed by the underlying pattern of the vacuum precisely so 
> as to correspond to my orientation of polarizers at angles which make 
> the particle experiment come out right?
>  
> And if i turn all control over to some kind of random event such as a 
> radioactive decay which could determine the polarizer angle then this 
> also would not be truly random, but again would be part of a solution 
> of the underlying equations of motion of the universe and by virtue of 
> that be magically bound to other pseudo-random events in the particle 
> experiment in such a way that the two local sets of events conspire to 
> produce a coordinated global consistency...?
> 
> Nostalgia for free will aside, this is unreasonable. My brain, a cat's 
> tail, and radioactive decay do not stand in the same physical relation 
> to the nearby particle experiment. The imagined bond is too magical as 
> it freely crosses from one level to another. After all, the connection 
> between the photon pairs, the cat's tail, and even the "random" events 
> was made in my subjectivity - where *else* is the link mediated?
> 
> What I am saying (and it has been said many times) is that this kind of
> conspiracy involves abandoning the type of connection on which science 
> is  based to a more profound degree than does acceptance of limitations 
> on the principle of locality.
> 
> rhett
> 
> 
> 
> references
> ----------
> 
> A. Einstein, N. Rosen and B. Podolsky, "Can Quantum Mechanical 
>             Description of Nature Be Considered Complete?" Phys. Rev. 
>             47, 777 (1935)
> 
> J.S. Bell, "On the Einstein-Podolsky-Rosen paradox" Physics 1 (1964)
> 
>            "Free variables and local causality" Epistemological 
>             Letters, February 1977 
> 
>            "Bertlmann's socks and the nature of reality" Journal de    
>             Physique, Colloque C2, 3, 42 (1981)
> 
>           ...all three reprinted in J.S.Bell, "Speakable and unspeakable 
>             in quantum mechanics" Cambridge University Press (1987)
> 
> Greenburger, Horne, Shimony, and Zeilinger, "Bell's theorem without 
>             inequalities" Am. J. Phys., 58, 1131-43 (1990)
> 
>                     ...in this regard see also sections 5.3 and 5.18 of    
>             R. Penrose, "Shadows of the Mind" Oxford (1994) 
> 
> H.P. Stapp, "Are superluminal connections necessary?" Nuovo Cimento,
>             40B, 1, 191-204 (1977)
>