On Fri, 2011-12-30 at 14:00 +0100, Vitkovsky, Adam wrote:
Well hopefully we won't need to worry about the speed of light anymore
Nope. The laws of physics as currently understood prohibit sending information faster than the speed of light. (The reality of FTL neutrino thingie is still too early to tell).
Basically when 2 photons or electrons are emitted form the same source -they are somehow bound/entangled together -that means if we change the spin on one photon to "up" the other photon will have it's spin changed to "down" immediately - and it doesn't matter whether the photons are next to each other or light years away -this happens instantly (no energy is transferred yet the information is passed) -this was already tested between two cities
That's not what happens: the entangled particles are in superposition state (i.e. they are carrying both |0> and |1> simultaneously). When the measurement on one of them is made, their common wavefunction collapses, leaving them in random specific state. I.e. if you measured one |0> the other will be |1>, or vice versa. Changing quantum state of an entangled particle to a known state will simply break entanglement (the story is more complicated, but I don't want to get into arcana). Because of that the quantum entanglement *cannot be used to transmit information* between receiving points, so this non-local action at a distance doesn't break the relativistic prohibition on FTL information transmission. However, this effect is still useful because it is a way to generate random encryption keys, which will "just happen" to be the same at both ends, hence the quantum cryptography. Anybody trying to snoop on the entangled photons in transit will cause premature wavefunction collapse which can be statistically detected (in practice sources of entanglement and phase detectors are not perfect, so quantum cryptography is not unbreakable).