Last night's Quantum Non-locality lecture was excellent. The hour passed by in what seemed like minutes - and I'm not quite nerdy enough that this would have happened if is wasn't a good talk.
Professor Popescu started out with a history of the subject. Einstein, assuming that non-locality could not exist, used it as Reductio ad absurdum proof that quantum mechanics could not actually be non-deterministic, and that the apparent non-determinism was actually caused by "hidden variables". But some three decades later John Bell showed that non-locality was in fact real - which also demonstrated that the hidden variables assumption was false.
This does not violate Relativity. Though the entangled particles may be said to have communicated faster than light, this correlation cannot be used to transmit information. Each of the individual particles continues to behave non-deterministically - it's only when their behaviours are correlated that you can demonstrate entanglement. So, it's the very non-determinism which allow non-locality to occur without violating Relativity.
This far, I'd managed to keep up, but the Professor then explained how non-locality could be measured - at which point, he shook me off entirely. So much for no mathematics!
I picked up his trail again soon, though.
Professor Popescu then explained some of the practical application that quantum non-locality might someday have. He went into some (though thankfully not too much) detail on teleportation. This won't, sadly, be too much like Star Trek teleportation, but the idea is that if you have entangled particles at some distance from on another, plus a normal, 'classical' communication channel, you can transfer another particle's entire quantum state from one place to another. This would not be possible by other means, since you cannot measure this state due to the uncertainly principal. The key is that you can transmit the state without ever measuring it.
Lastly Professor Popescu told us about what he's currently working on. It's to do with a perceived problem with Quantum Physics' axioms.
Relativity is dependent upon only two, elegantly simple axioms - that the laws of nature are the same for all observers that move with constant speed relative to each other; and the other was that the speed of light is finite and the same for every observer.
Quantum Mechanics' axioms are not quite the same. For example the first axiom is utterly incomprehensible to most, and complex even to the experts. Professor Popescu is hoping that, just as non-determinism allows non-locality to occur without violating Relativity, perhaps one can take Relativity and non-determinism as starting points, and derive Quantum Mechanics. Beautiful!
Next week, Not just about numbers.Posted to Science and technology by Simon Brunning at October 14, 2004 04:24 PM