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Comment by Neil_B. on The Born Probabilities · 2008-06-09T02:07:36.000Z · LW · GW

Consider for example what "scattering experiments" show, in a context of imagining that the universe is made of fields and that only "observation" makes a manifestation in a small region of space? I mean, suppose we think of the "observations" as being our detecting the impacts of the "scattered" electrons rather than the scatterings themselves. (IOW, we don't consider "mere" interactions to be observations - whatever that means.) But then why and how did the waves representing the electrons scatter as if off little concentrations when they were interpenetrating? And, what of the finding that electrons are "points" as far as we can tell, from scattering experiments? Note that the scattering is based on imagining one charge "source" being affected by another source's central inverse-square field, nothing that makes a lot of sense in terms of spread-out waves. Note also that the scattering is not a specific "impact" like that of billiard balls, since it is a matter of degree (how close one electron approaches another, still not touching since they don't have extensions with a discontinuity like a hard ball - and the very term "how close" betrays an existing pointness.) And so on ... IOW, it's worse than you think.

On a different note, it is supposed to be impossible to find out certain things about the wave function, like its particular shape. We are supposed to only be able to find out, whether it passed or failed to pass the test for chance of a particular eigenstate (like, a linear polarized photon having a greater chance of passing a linear filter of similar orientation, but we wouldn't be able to find out directly it had been produced with a 20 degree orientation of polarization.) However, I thought of a way to perhaps do such a thing. It involves passing a polarized photon through two half-wave plates over and over, say with reflections. The first plate collects a little bit of average spin from each pass of the photon, due to the inverting of photon spin by such a HWP. The second HWP reverts the photon's spin (superposed value, the "circularity") back to it's original value so it will reenter the first HWP with the same value of circularity each time.

After many passes, angular momentum transfer S should accumulate in the first plate along a range of values. S = 2nC hbar, where n is number of passes, and C is the "circularity" based on how much RH and LH is superposed in that photon. So for example, a photon that came out of a linear pol. filter would show zero net spin in such a device, elliptical photons would show intermediate spin, and CP photons would show full spin of S = 2n hbar. It isn't at all like having eigenstate filters. Having an indication along a range is not supposed to be possible (projection postulate), and is reminiscent of Y. Aharonov's "weak measurement" ideas.