From: jlg@cochiti.lanl.gov (Jim Giles)
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Organization: Los Alamos National Laboratory
Date: Thu, 10 Sep 1992 19:57:55 GMT

In article <268@mtnmath.UUCP>, paul@mtnmath.UUCP (Paul Budnik) writes:
|> In article <1992Sep9.223637.24769@newshost.lanl.gov>, jlg@cochiti.lanl.gov (Jim Giles) writes:
|> 
|> >  The possibilities locally are "a particle
|> > is detected" or "a particle is not detected".  The same possibilities exist
|> > at the distant end.  How does our local observation allow us to determine
|> > the distant result?  The widest range is "detection/non-detection", so is
|> > `limited' range *after* the local observation is made.  In other words,
|> > you haven't narrowed the possibilities at all.
|> 
|> To test bells inequality you must determine if certain bit streams are
|> correlated. [...]

Which you can only do if you compare the streams *after* the fact.  That is,
the streams are transmitted in an ordinary way after they are produced.

|> [...]  The information that produced that correlation was transmitted
|> instantly at the time an observation was made.  [...]

By that logic, hidden variable theories *also* involve instantaneous 
transmission of information.  If I have a queen of spades and a queen
of hearts, give one to an astronaut and put the other in a safe, later
I remove the one from the safe and look at it - I *know* what the astronaut
has too - even if he's light-years away.  Did this "information" travel
instantaneously?  No.

|> [...]                                            If no information was
|> transmitted the bit streams would not be correlated. [...]

The particles traveling away from their common source carry the
correlation in an unknown way - whether this be faster-than-light
hidden variables, a *local* connection between the particles in some
"higher dimension" (whatever that even *means*, physically), instantaneous 
"wavefunction collapse" (whatever *that* even means, physically), many
worlds, or some as yet undiscovered method.  This is the very question 
which makes this issue controversial.  Since *instantaneous* action
is present in only *one* of these untestable models, it is premature
to state that it has definitely happened.  In fact, I see nothing 
*different* about a faster than light hidden variable and the
"wavefunction collapse" models - they seem identical to me.

In the meantime, I still don't agree that information has actually 
been transmitted - only that a post-hoc correlation exists.  Can 
you characterize how many bits of information you are claiming was 
transmitted?  Information can be measured, so this should be a simple 
exercise with the math involved.

|> 
|> >...
|> > There is no such Effect.  A local observer cannot tell whether the distant
|> > polarizer is being manipulated or not - or vice versa.  The only thing you
|> > can say is that _after_ the fact, the aggregate results of many trials of
|> > the experiment will obey a certain correlation. ...
|> 
|> It is a fact that a distant manipulation instantly produces a local affect
|> according to the instantaneous collapse postulate. 

Which is only one among many empirically indistinguishable models.  And the
local "effect" is not locally observable.  So it can't really be described 
as a local effect at all.  This is just another way of stating the problem:
something is happening which we don't have an explanation for - a non-local
phenomenon with no (apparent) local effects.

|> This violates either Lorentz invariance or causality. Several physicists
|> writing in this area have made this point. If you do not believe me, please
|> read the relevant literature. This is discussed in great detail and very
|> clearly in P. H. Eberhard, Il Nuvo Cimento 46 B, 392, (1978).

Oh, I agree entirely that the EPR phenomenon *rules*out* certain older,
mechanistic models.  It does not automatically, as a consequence, prove
any of the known (or unknown) alternatives to these older models, none
of which are yet empirically testable.

|> > [...]
|> > I agree with you about the undesirability of mystical solutions.  But,
|> > at present, there is no *objective* reason for preferring *any* model
|> > that has been proposed.
|> 
|> It seems to me that you just gave one. Objective models even incomplete
|> ones are preferable to mystic solutions. Local models are certainly
|> preferable to those that are not.

I consider the "wavefunction collapse" itself to *be* a mystical 
solution.  It requires the postulation of the *real* physical existence 
of a mathematical abstraction - a physical existence which is *inherently* 
untestable.  In my mind, the very definition of "mystical" is "anything 
reliant on inherently untestable assumptions."

|> [...]
|> Experiments will ultimately decide the result and we must always reserve
|> final judgement for that verdict. But science only makes progress if we
|> pursue the paths that seem most likely given the limited knowledge we have
|> at any time.

Reliance on something which is said to be inherently untestable - even 
by its supporters - doesn't seem to me to be likely to promote progress 
*at*all*.  Much less does it seem to be "most likely given the limited 
knowledge we have at any time."  I mean, since the "wavefunction collapse" 
*supporters* claim that the thing is inherently usobservable, what 
leverage does this give you toward a solution?

|> [...]
|> I think most physicists agree with you that
|> there is an objective cause for quantum collapse. What they do not seem
|> to realize is that this implies that quantum mechanics is, as Einstein
|> always said, an incomplete theory.

Then we should agree that it's incomplete and look for *objective*
ways of completing it without making arbitrary and untestable attempts 
to give a pretense of completeness in the meantime.  The correct answer
to the question about what causes the correlation is "we don't know."

-- 
J. Giles
Newsgroups: sci.physics