Tim May wrote...
"I don't believe, necessarily, in certain forms of the Copenhagen Interpretation, especially anything about signals propagating instantaneously, just the "quantum mechanics is about measurables" ground truth of what we see, what has never failed us, what the mathematics tells us and what is experimentally verified. Whether there "really are" (in the modal realism sense of Lewis) other worlds is neither here nor there. Naturally, I would be thrilled to see evidence, or to conclude myself from deeper principles, that other worlds have more than linguistic existence." Yes, this has been a fashionable set of statements, very smiliar to "quantum mechanics is merely a useful tool for calclating the outcome of experiments". I used to chant this too, but the recent (well, over the last 10 years) experimental work in EPR has convinced me that there's really something odd going on here. "Many worlds" (first proposed in the 50s and recently revived) is one possible explanation for why, for instance, photons in the double slit experiment "know" about the slit they didn't go through. And while I am not particularly convinced that this is the explanation (there are other basic things about the QM world it doesn't explain, such as why I measure THIS outcome rather than THAT outcome), I'm personally at the point where I think some form of answer is needed, and that the above intellectual dodge is no longer valid. So at least many worlds is one possible attempt to answer why photons are able to "know" instantaneously about correlated photons far removed (and for me, and the late John Bell it is inescapable that they do indeed find out instantaneously). One way out is to ditch quantum mechanics as being anything near a "description" of reality as classical theories in essence are. Tim Boyer of CUNY and a batch of Italian researchers have done a pretty convincing job of showing that Ahranov-Bohm can be classically derived in a fairly straightforward manner. But it doesn't explain how AB is able to predict said phenomenon in about 4 lines while they need many pages of fairly difficult E&M theory. For me it's clear that A/B and EPR show us that QM is telling us SOMETHING about reality, but we don't yet understand what it is.
