From: ydobyns@phoenix.Princeton.EDU (York H. Dobyns)
Subject: Re: Can quantum terminology be flakeproofed?
Originator: news@nimaster
Organization: Princeton University
Date: Tue, 13 Oct 1992 17:06:26 GMT

In article <mcirvin.718939413@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:
>Part of the problem is that physicists are by no means of one
>voice about what really happens when an apparatus measures something.
[...several views briefly summarized...]
> Most of these views
>seem to be more or less equivalent in terms of predicted outcomes
>for experiments.

It's worse than that. For basic QM, *all* of the different philosophical
interpretions are *exactly* equivalent in terms of experimental
predictions; the formalism is the same, only the presumed meaning of the
terms differs.

One of the few areas where the models might actually differ, according
to some recent analyses, is in nonlinear QM; but whether this is
actually relevant to the real world depends on whether or not there
actually are any phenomena described by a nonlinear variant of the
Schrodinger equation.

>Almost no physicist thinks today that consciousness has anything to
>do with the act of measurement.  (You might say that the apparatus,
>like the famous cat, is in a superposition of macroscopic states until
>a conscious observer observes it; but why in heaven do you have to
>make the "collapse" happen *there*?)  

This is the "von Neumann chain" argument. Apparently John von Neumann,
somewhere in his definitive work on the mathematical foundations of QM,
tried to address the question of what constitutes an observation; that
is, where in the sequence of events in an experiment do we go from the
probabilistic superposition described by a quantum wave function to the
single, definite event that characterizes human experience? He reasoned
that Bohr's viewpoint, or the Copenhagen interpretation, with its strict
dichotomy between classical and quantum systems, was untenable--since
every physical object can be described by a sufficiently detailed
quantum wavefunction. Von Neumann's reasoning was that every step--from
the scattering particle, to the electronic cascade in one of the
detectors, to the response of the indicator connected to the detectors,
to light scattering off the indicator and being absorbed in a human eye,
to neural responses in the eye leading to events in the brain--every
one of these events is one quantum system interacting with another
quantum system, and the whole morass can be described by a sufficiently
complicated wavefunction if you're determined enough, and you'll end
up with a human brain in a superposition of states. The only place
von Neumann saw to break the chain of quantum interactions is where
brain events become conscious perceptions, because here, finally, we
have an interaction with something that isn't just another quantum
system--as far as von Neumann was concerned, there is no current
physical model or even representation of consciousness, so there's no
reason to expect it to obey the laws of QM.

>[...]  I think that this interpretation has little
>reasoning and no evidence in its favor (as you nicely summarize)

The reasoning, or at least my crude rendition of von Neumann's reasoning, 
is presented above. The evidence? There can't be any evidence to favor 
one QM interpretation over another, because all of the interpretations are
attempts to come up with a sane way of thinking about the *same*
formalism. The mathematics of QM appears to be correct in every
particular, the problem is that it seems to describe a world of
probabilistic amplitudes that is entirely at variance with the way
human beings experience reality. You're always confronted with the
problem of deciding where the probabilities described by the QM
formalism turn into the actual events we see at the human scale. 
That transition has never been part of the formalism, and can apparently
be stuck in on an ad-hoc basis almost anywhere without making a real
difference in the predictions of the theory.

>Everything written about this subject tends to become seriously
>mangled in the popular literature, since the consequences often
>seem so bizarre.  

You think the popular literature is mangled? The professional literature
isn't much better off. I recommend John Bell's "Speakable and
Unspeakable in Quantum Mechanics" as a good survey of some of the
alternatives people are considering. "Philosophical Consequences of
Quantum Theory: Reflections on Bell's Theorem," eds. Cushing and
McMullin, is another good references.  From what I can tell--and I'm a
physicist myself--no matter what position you adopt for interpreting
QM, you can find some segment of the physics community that completely
disagrees with you.

>>I'd like  to see some  of the Heavy  Hitters of Physics  come out
>>with  quotable (and  above all  *understandable* statements about
>>the nature of 'observation', so that people will realize that the
>>universe *does*  still exist independent of  the consciousness of
>>the observer.

Sorry, I lost the attribution on the person Mcirvin is quoting here.
Whoever you are, good luck: you'll need it. I quote N. David Mermin:
  
  "The questions with which Einstein attacked the quantum theory
  do have answers; but they are not the answers Einstein expected
  them to have. We now know that the moon is demonstrably not
  there when nobody looks."
	("Quantum mysteries for anyone", Journal of Philosophy
	78, 397 (1981), p. 397-408, reprinted in _Boojums_All_The
	Way_Through_, a collection of Mermin's essays published
	in 1990. Lest you mistake Mermin for a crank, he's a
	professor of physics at Cornell; of the the 26 essays in
	_Boojums_, 11 are reprinted from Physics Today, 7 from the
	American Journal of Physics. One entry is reprinted from
	the Cushing/McMullin anthology mentioned above.)

Mermin is no big fan of the consciousness of the observer; I'm sure
he would regard an automatic camera as an adequate case of "somebody
looking" for purposes of the quote above. However, the point Mermin
makes in his essays about Aspect-type experiments is that certain types of 
extreme objectivism have been experimentally refuted.  Regardless of the 
ultimate truth, falsehood, completeness or otherwise of QM, Einstein's view 
of a universe in which there are locally real events without "spooky 
actions at a distance" has now been *observed* to be false, for the 
universe we live in.

York Dobyns		ydobyns@phoenix.princeton.edu
Newsgroups: sci.skeptic