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RE: Explaining QM to the layperson



I don't understand "could have". Schrodinger's cat lays it on the line.
Either you are an objective realist or you are not; it's that simple.
What you must recognize is that some belief structure is necessary to the
interpretation of Nature. I am a realist; I believe in objective realism
without reservation. Schrodinger's cat in its mixed state is anathema in
my belief structure, but it is a logical interpretation in the Copenhagen
faith. I reject the Copenhagen faith.

Leigh

And Paul Camp replied:

Interesting arguments and you certainly have good historical company
making them. However, I am still unclear on how a realist interprets
the wave function? What is doing the waving when a wave function
waves? One should take note of the fact that Yakir Aharonov has
recently been making noises about being able to measure the wave
function of a single particle so some statistical ideas may be on
shaky ground. (I heard this in a colloquium about 2 years ago).

Paul, I think you're baiting me. Your not a closet Bohmian, are you?
I'm an experimentalist; this sort of stuff comes hard to me. Please
be gentle!

The statistical position is minimal. As you no doubt know, it does not
interpret the wave function at all for an individual case. The wave
function only has meaning for an ensemble of identically prepared
systems, and then it only interprets the amplitude and not the phase.
The phase can be detected separately, perhaps for individual pairs of
particles, or at least the phase shift for pairs of particles (or
ensembles of pairs of particles - I don't know of any way to do good
statistics on single pairs). This latter point may be what Aharonov
was talking about. Leslie Ballentine in our Department is an expert
in this area (and the leading evangelist for the Einsteinian view).
If you can formulate a good question for me to ask him I'd be glad
to do so.

Second question: is it necessary for a realist to believe that he is
independent of that which he observes? That's the classical idea but
it isn't clear to me what you are promoting.

There are two answers to that question. The observer is independent of
the system he *will* observe; the outcome of a subsequent observation
does not depend on the observer's state of mind or his intent regarding
the future observation. That is the classical idea, and I don't yet
have reason to doubt it (and yes, I am aware of Alain Aspect's work).
The foregoing is a statement of belief which has the dubious status of
being common sense also.

The second answer is that I acknowledge no measurement of a system can
ever be made without interaction between the observer and the system.
In that sense they are not independent of one another. There must be
some effect, but I'm still advocating the idea that the interaction is
causal. My faith in this matter is capable of admitting change if/when
more evidence accumulates, but it is not yet time for me to switch. I
have done it before. I relinquished conservation of parity only one
semester after first learning of and embracing it; I'm older and more,
er, conservative now.

Interpretation of the Aspect experiment is not transparently simple,
at least to me it is not. The earlier work of Clauser and of course
Bell's theorem all need to be simplified for my consumption. If you
can explain all of this in terms *this* relative layperson can
understand you will be doing a valuable service to me and all others
similarly benighted on this list.

Leigh

(I see your next post suggests Mermin's book, which I haven't read.
He gave us a talk about red and green lights a few years ago. I have
followed less tricky explanations better than Mermin's, but perhaps
I should try again. At one time I did convince myself that Bell's
theorem is valid, so I've come that far. Interpreting Aspect's
experiment in terms of Bell's theorem is a step I haven't made yet,
and I believe that is what Mermin was doing with his lights.)