From: platt@watson.ibm.com (Daniel E. Platt)
Subject: Re: Why do physicists make preposterous predictions?
Date: Thu, 01 Oct 1992 19:39:34 GMT
Disclaimer: This posting represents the poster's views, not necessarily those of IBM
Organization: IBM T.J. Watson Research Center

In article <300@mtnmath.UUCP>, paul@mtnmath.UUCP (Paul Budnik) writes:
|> In article <1992Sep29.162439.18453@watson.ibm.com>, platt@watson.ibm.com (Daniel E. Platt) writes referring to my article.
|> > 
|> > This is not entirely accurate.
|> > 
|> (Argument deleted.)
|> 
|> Bell's result depends only on the macroscopic experimental
|> predictions of QM. You can only escape his result
|> with a theory that makes different predictions. It does not matter if
|> the state vector is real or not. It is the predicted macroscopic results
|> that involve action at a distance. It is strange action at a distance
|> since you cannot use it to send a signal but is nonetheless action at a
|> distance.

It isn't 'action at a distance.'  It is correlated information (while
not deterministic or complete) about what two isolated observers could
observe.  It doesn't matter whether the observation is space-like or
time-like, and is not a causal connection.

|> 
|> >... 
|> > Depends on whose development of QM you read.  In part, the above argument
|> > implicitly assumes that the state vector must ultimately convey the information
|> > of what was measured by each observer to the other observers.  Actually,
|> > the only information it is carrying is what cannot be observed by both
|> > observers -- even over space-like intervals.
|> 
|> I am assuming nothing about the underlying mathematics of quantum
|> mechanics. We observe local detections and the angles of a
|> local polarizer. This tells us something about the probabilities of
|> combinations of polarizer angles and detections that have occurred at the
|> remote site. This knowledge or information had to be transmitted
|> instantaneously.
|> 

A very good development of QM can be made without any explicit or implicit
reference to collapse.  Gasiorowicz's text on Quantum Mechanics (published
in 1974, don't remember publisher), is a great example of this.  As with
any <mathematical> system, collapse as an aspect of measurement is a
postulate that can be relaxed or removed, and then the system can be
studied without the postulate (similar to the odd geometries without
the parallel postulate).  In terms of being a good description of
reality, 'collapse' as defined by the postulate doesn't look like a good
fit.  Lots of other descriptions of measurement, such as Feynman's, 
Gasiorowicz's, Schiff's, etc, don't suffer from those problems.

|> > What do you mean a wave function (state vector?) 'was there all the time'?
|> > Here, again, the assumption is made that the state vector must ultimately
|> > carry the information of what measurement was ultimately made to all observers.
|> I was simply allowing space for variations on Everett's interpretation. I
|> would never attempt to defend that or any other interpretation of quantum
|> mechanics. This is because I think what they are interpreting is false.
|> 
|> >...
|> > 
|> > "Preposterous?"  Sounds a tad emotional... the word keeps coming up...
|> 
|> It is intentional and appropriate. The predictions are preposterous
|> given the lack of experimental or theoretical basis for them.

There's lots of physicists who don't subscribe to the postulate as stated.
What is inappropriate is assuming every physicist accepts non-unitary collapse
as a mechanism, separate from they dynamic Hamilton/Schroedinger equation,
that can modify the state vector.

|> 
|> > One of the elements in this line of argument is that it fails to
|> > recognize that there is a spectrum of responses that have been
|> > taken to the assumptions listed above.  Some of them are better
|> > than others.  I find it a bit surprising given that it was
|> > acknowledged that physicists don't seem to agree on all the points
|> > of interpretation.  Particularly, you can have two physicists see
|> > the same results, say they agree on what the results were, and then
|> > disagree on whether it means the photon state vectors collapsed.
|> 
|> Almost all physicists agree about the experimental predictions. It is
|> these predictions, not the underling model, that is the problem.

Here, you'll find that I agree with the predictions.  The point we don't
seem to agree on is whether the observation of correlated spins over
a space-like interval requires a transmission of information between
the observers.  I claim it doesn't.  So does any physicist who does not
subscribe to collapse.

|> 
|> > |> 
|> > |> I suggest two answers. This first is best understood through
|> > |> the Hans Christian Anderson fairy tale *The Emperor's New Clothes*.
|> > 
|> > This would be fair if everyone agreed, and nobody argued.  As it stands,
|> > most people argue, and not everyone agrees.  Consensus has not been
|> > achieved -- for what ever reasons.  This implies that most people are
|> > aware of the problem with the clothes; however, most people have 
|> > acquired some degree of comfort or acceptance of the situation.
|> 
|> Most physicists seem to have reached a consensus against Einsteins position
|> regarding objective reality. If this were not true, tests of Bell's
|> inequality would be a much higher priority. Of course they do not agree
|> on what to replace objective reality with. That is because none of the
|> alternatives make any sense. None of them can be defined with
|> mathematical rigor.

No, most physicists seem to agree on objective reality, according to
a recent poll on the topic.  What they disagree on is the level of 
ability to describe it.  In other words, they are happy to allow
quantum mechanics to be able to communicate conservation of observed
energy over space-like intervals without requiring information to
be communicated between the two observers.  The information in the
state vector shared by both observers is that the cross-section for
events that violate energy conservation or angular momentum conservation
is zero.  It does not have to 'collapse' for this information to be
inherent in the state vector.

|> 
|> > ... Unfortunately for it, the
|> > |> non preposterous (local Lorentz invariant collapse) version of quantum
|> > |> mechanics is an explicitly incomplete theory. It implies that the wave
|> > |> function has an objective physical reality.
|> > 
|> > Does it?  That's one interpretation... not one that's universally held.
|> 
|> If the wave function has an experimentally observable, through tests of
|> Bell's inequality, local structure this would be compelling evidence
|> for its objective reality.

The above statement does not parse.

The only issue is collapse, and the objective reality of collapse.  This
seems to remain an open question.  In a way, you're in a strange position
trying to convince me that quantum mechanics requires collapse so that
you can shoot it down, while I don't believe in collapse (at least, as
described by Dirac or by Cohen-Tanoudji or by Sakurai).

|> 
|> >... 
|> > Wouldn't they? I expect there are quite a few who accept objective reality.
|> >...
|> 
|> I mean objective reality in the sense that Einstein used the term. The
|> current formulation of quantum mechanics is an incomplete description
|> of an underlying objective reality. I do not think all physicists reject
|> Einsteins approach. Most seem to. 

How substantial is something that eludes our ability to achieve consistent
description?  This is a question of epistomology.

|> 
|> > ...
|> > I suspect that this is the reason the question has 
|> > persisted so long without the emergence of some consensus -- it isn't easily
|> > measured; most of the time it is irrelevant; it is likely not going to change
|> > the utility of the results of QM as currently developed.
|> 
|> I do not expect anything to overturn the usefulness of existing results.
|> If quantum collapse is a physical measurable process, than understanding
|> its structure is likely to be of enormous theoretical and practical
|> importance. Bell's results provide an initial experimental window
|> on this structure. Who knows what physicists will find once they
|> start looking. No one at the birth of quantum mechanics would have
|> suspected it would lead in a few decades to powerful inexpensive computers.

I don't think quantum collapse is a real process.  Maybe it is; if it is,
I'd be surprised.  However, there have been some interesting papers
recently studying the coupling of quantum systems to classical chaotic
systems, that seemed to demonstrate collapse.  However, a recent citation of
this in the Statistical Mechanics literature put that collapse in quotes when
they discussed it, which seems to indicate that *THEY* don't think of it
as a demonstration of collapse in the sense of the old debate.

To some extent, we've had this argument before.  I've had more time to
think about the questions, and its given me more time to come to understand
some other positions, such as Feynman's position and its reflection in
his path-integral formulation of quantum mechanics.  But I still have
one question for you:

	What is the Hamiltonian for measurement?  Or, what is your dynamic
	description of measurement?  Or, how do you interpret the results
	of QM if you believe that most of the results of QM will be preserved?


Dan Platt
Xref: sparky sci.physics:15879 sci.astro:10401 sci.math:12669 sci.philosophy.tech:3545