could a simple experiment lay to rest the old idea of metaphysical observers?

Does the current state of real experiments in quantum foundations
already make it totally obsolete and wrong to talk about "metaphysical
observers" the way that Copenhagen people do?

My wife rightly keeps reminding me that I sometimes jump ahead too
much, without really cleaning up the elementary points which people
need to understand and justify more completely first.

And so.. I have good practical reasons, I think, for discounting
metaphysical observers, but maybe it would be useful to do actual
experiments to really nail down the point in an easier way to
understand. Since ... is not SO far away from Professor Yamamoto
(emeritus Stanford), it is possible that he might have ideas for THAT
kind of experiment, as I will explain.

Let us begin by asking WHAT ACTUALLY HAPPENS in a very simple kind of
experiment: we have a source of photons emitting light at a certain
rate, at a certain (linear) polarization. That light is sent to a
polarizer, after which there is a detector, and a human looks at the
readout from the detector. For simplicity, assume the photon has an
initial polarization of angle tau, while the polarizer is tilted to
want angle theta to pass through.

It is well-known that the intensity of light at the detectors will be
cos**2(tau - theta), so we know how the experiment comes out. But
there are fiv e theories of what is happening here, which need to be
tested against each other (in DIFFERENT experiments).

According to the old metaphysical Heisenberg version (even if updated
a bit), the wave function of the photon BEFORE the polarizer is just a
nice pure wave,
for polarization tau, with a wave function denoted as |tau>.. The
polarizer then
performs a "unitary operation," rotating the wave function. What comes
out is the wave function a|theta>+b|0>, where |0> means "vacuum state
(no photon there), where a is some complex number like cos(tau-theta)
and where |a|**2+|b|**2=1.

In the Heisenberg theory, what comes out of the detector is ALSO a
mixed state, with a|detection>+b|no-detection>, if it is a perfect
detector. The wave function "collapses" into a human seeing a
detection or a human seeing no detection, only when a human actually
looks at what comes out of the detector.

So that's theory number 1. Let me jump to theory number 3, KQED, my
understanding of the best mainstream version of QED actually used
today. According to KQED, what comes out of the polarizer is ALREADY
collapsed.
What comes out is a density operator, representing a simple classical
probability of |a|**2 that the wave function coming out is just
|theta> and a probability of |b|**2 that nothing comes out at all. In
fact, all the well-known "predictions of quantum mechanics" for the
classic Bell's Theorem experiments used this assumption in doing the
calculations. (I have papers at arxiv which review those calculations
in detail.)

I have put a lot of effort into lobbying for two experiments which
would decide which is true, theory 3 or theory 4 (which I haven't
mentioned yet in THIS post),
but what about deciding which is true, theory 1 or theory 3? (No, it's
not just a matter of interpretation.) What about a possible theory 2,
where the polarizer is unitary but the detector is not?

In fact, there are physical consequences to the idea that |theta> and |0> may be
superposed, like entangled in a way, together. So by testing those
consequences, could we lay theory 1 to rest in a way clear to
everyone, once and for all?

Since theory 1 strikes me as silly, for many reasons, I haven't put
much effort into this myself, and I don't plan to. But since theory 1
is such an article of religious faith for so many people, maybe it
would be good for SOMEONE to aim for such an experiment. It is even
conceivable to me that a very clear experiment has already been done,
and not published because it would be seen by some as a "negative
result."

Above all, I think I remember seeing some paper by Yamamoto, a highly
respected researcher, talking about exploiting states of the form
a|theta>+b|0> in quantum computing. Could it be that HIS lab has
examined this? Perhaps it is a simple matter of persuading people in
his group that results they already have SHOULD be brought forward, as
the decisive test of alternative basic theories which they are, and
published. (Not that the thoughts of graduate students doing such work
are really simple!) Or perhaps it is something close enough at hand in
his lab that he could do it. Or perhaps someone else on the list
connected to a place which does such work could do it.

Who knows?

Again, it is not at the core of my own emphasis, which does not give
credence to theory 1 anyway.

Best of luck,

   Paul

P.S. For those who might ask... theory 3 basically would represent the polarizer as a solid state object which "condenses the wave function" in the usual way they teach in quantum mechanics 1. In my papers at arxiv (published at SPIE and elsewhere), I showed how that idea can be translated into a "master equation" like what is standard in real quantum optics these days, having the same effect. But I also showed a DIFFERENT master equation, with DIFFERENT effect, a different model of what the polarizer does. That simple difference in models was, last year, the only clear difference between KQED and my proposed variation, MQED. Just a matter of characterizing what polarizers ACTUALLY do. But if they do what I think they do, the implications are very far-reaching, because it proves that the models we use for ALL solid state components in quantum optics need to be revised, in a way which opens the door to all kinds of new technology. This past year, I added a near-trivial new model for black body radiation sources, and proposed another simple experiment to test that one, with wilder and crazier and easier properties. That's theory 4. Theory 5 would be **IF** a deeper Einstein/Lagrange type of unified model could be found, for which MQED would only be an approximation.