With all due respect, Pooey Dr Mike. Take a nice, straightforward EPR using two correlated photons produced by KDP-downconversion. How do you exaplain the EPR experiements where pairs of photons are created via KDP downconversion? The two particles are separated at birth and travel through different paths through the apparatus. (And this apparatus can be made aribtrarily large.) If the apparatus does not permit us to determine the path of any single photon, the two photons will have completely coupled measureables (eg, polarization) at the output. The moment will are able to determine the path of ONE of the photons, then the measureable of the other becomes completely de-correlated from the other. This is true on the single photon level, and looked at up close its pretty startling.Part of the problem is that the detection equipment is many fermions looking at single particles. I think QM is easier to understand when looking at an ion trap. There are lots of photons around for every atom but the interactions are with fields and the detection is of single photons (again with massive amounts of equipment, but the atoms don't interact directly as in EPR or double slit).
Now the odd thing (if this isn't odd already), is that we can (and have) perform the change from isolatable to nonisolatable AFTER THE PHOTONS HAVE ENTERED THE APPARATUS. (This was suggested by Wheeler and done around '94 as I remember). In a sense, then, the photons are 'aware' of events happening (relatively speaking) backwards in time. And this is not theoretical. It was predicted via quantum theory and seen in the lab many times.
Now obviously we could step back and say that "QM is a useful computational tool. Let's not worry about reality", but that's an intellectual dodge. Classical physics grew up around the desire to understand natural reality, and this "new" fad of ignoring what QM says about reality only arose as a way to move QM forward in the early days. Look, it's not like we say "Don't think of light as an electromagnetic wave. E-M theory is merely a useful computational tool". Likewise just because we are in the odd situation of not knowing what QM says about the universe doesn't mean its not saying anything, or that what its saying is of no interest.
With EPR (and, arguably, A-b), we are confronted with obvious "proof" that these particles communicate in ways that are completely different from the models developed prior to 1910 or so. (One of the few intelligent thoughts I've had on the subject is that the particles are still a single quantum object prior to measurement.)
With respect to Cypherpunks and cryptography, then, we would be intellectually hypocritical if we thought there was anything inherently more secure about quantum cryptography. But we (I mean, pretty much every working physicist in the world) DO believe this, because this is really the way reality "works". Wavefunction collapse actually "objectively" (if that's the right word in the quantum world) happens and there's no undoing it. It's a basic physical property of the universe.
With respect to many worlds, David Deutch, et al have argued that for any single path taken by a particle in a quantum there are innumerable "shadow photons" in the other universes that communicate with the observed photon. We also see just one possible but the complete collection of shadow photons take all possible outcomes. Now while I don't really buy this explanation, I DO buy Deutch's desire to find a picture of the underlying reality (we once spoke on this issue and wildly agreed).
I could go on but I've got work to do. No one's actually read this far anyway, have they?
-Tyler Durden
QM is a nice model that works. It is a good mathematical description of observed phenomena. What else do we need? The idea that a photon "passes thru" one slit or the other is just a model. What is the slit? It's really a whole bunch of fermions in a spacial pattern, and when an electron or photon interacts with that distribution we get the observed "self interaction" result. The model is self interaction. That may have nothing to do with reality.Patience, persistence, truth, Dr. mike
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