donald (08/05/82)
I hate to bring up the old quantum mechanics debates again, but quantum tunneling IS instantaneous, at least in some sense of the word. A particle which appears on one side of a potential barrier at a particular instant can be detected on the other side at some future instant which is arbitrarily close to the first instant. (for you diehard quantum theorists out there, I know I'm over- simplifying, but bear with me...) There is no "transmission" across the barrier in the usual sense of the word, not even of "wave function" waves (!) as was suggested in a previous article. However, it would appear that as a real FTL mechanism this is useless because no information can be transmitted. Sometime ago a French physicist named Aspect was planning an experiment to test the Bell inequality which might demonstrate the existence of "correlated space-like events" (sorry for the technese). This might be interpreted to represent superluminal (FTL) information transfer between two points. Does anyone know how it turned out? (What do supernovas and gravity propagation have to do with FTL???) Don Chan
miles (08/06/82)
Quantum tunneling is NOT instantaneous in any sense of the word. "A particle which appears on one side of a potential barrier at a particular instant in time...", the instant in this is a completely different instant as in 'instantaneous'. The word instant in this statement should be replaced by 'point in time'. And as for the instantaneous travel, which would be suggested by no "transmission"... , it does take the particle finite time to cross the barrier, the measur e of time is to small to measure by conventional, standard timing devices, so out of convenience one says it is "instantaneous", although it is not. It could be measured, but one would need a very,very acurate timing device. And yes, there is transmission. The particle is not prese nt at one barrier, and then just appears at the other barrier. Raymond S.
donald (08/06/82)
Argh. Here comes a rehash of net.misc of a few months ago. Quantum tunneling of a particle through a potential barrier does not involve "transmission" in the usual sense of the word (I am addressing Raymond, utzoo!miles) because it does not involve *any* movement of matter or energy through the gap. All that happens is that at one moment you see the particle *here* and the next moment you see it over *there*. My use of the phrase "instant of time" has mislead Raymond; it has nothing to do with instantaneous, it just means "moment in time". As for my claim that the process of tunneling is instantaneous in some sense, note that there is no implicit "transit time" in the appearance of the particle on the other side of the barrier. The collapse of the wave function is instantaneous. In other words, the events of disappearance and reappearance are space-like events. Once again I must apologize for an oversimplified description of quantum processes. On the topic of FTL, an interesting philosophical note: Why are people so hopeful about the existence of FTL and indifferent about the law of conservation of energy? It seems to me that people will bend over backwards to try and find a loophole in physics or some specious argument that will al- low FTL to exist, but when it comes to violating energy conservation (e.g. perpetual motion machines), anyone suggesting it is labelled a crank! Don Chan