On Tue, 31 Dec 2002, Tyler Durden wrote: > Actually, Tyler Durden (ie, me) wrote what is attributed to the generic > anonymous name of Norman Nescio. Anyway,...
Yeah, the TD gave that away :-) > 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 Easy, the particles are correlated at birth. *they* know what their orientation is, it is fixed at birth. The math says *we* don't know. > 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. It is not suprising to me. The photons are correlated to begin with, when you learn one you know the other. You don't even have to measure it for a long time, you can know what it will be in 100 years if you can store it that long. > 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. Right, because they are correlated at birth. Once correlated, always correlated. The apparatus has nothing to do with it. > 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. There's more than one way to look at things. That's all QM says. It also tells us reality is tied together, you can't separate energy-time or space-momentum. We grew up with classical ideas, we have to let those ideas go to accept QM as "reality". > 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.) They don't need to communicate. That's the problem with the model. They start out correlated with a fixed orientation and maintain that correlation forever. > 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. What's more secure about QM is that you destroy the ability to use a data bit once it's been measured - you can't cut and paste. It has nothing to do with wave functions or collapse - it has to do with the fact that one side has already measured each one of the matched pairs and the other side hasn't. If Eve takes out data, it can't be used for transmission. You can still use spys and bypass the crypto :-) > 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 never really like the "many worlds" model. Feynman (sp??) diagrams work just fine for me! > I could go on but I've got work to do. No one's actually read this far > anyway, have they? Nope :-) Patience, persistence, truth, Dr. mike
