Hello all, I'm having a couple of problems with interpretations of Quantum mechanics and just want to summarise my understanding so that it can be verified and/or corrected. Schroedinger's cat leads to the idea of entanglement, namely the observation of one event indicates that other events have occurred. (seeing a dead cat means that the poison was released. Likewise, measuring the spin of one photon may give a measurement of the spin of another (entangled) photon. Bell's theorem states that there cannot be a theory (which predicts the correct result of experiments) using local hidden-variables. Is that the same as saying that the spins have no value before they are measured? Or if they do, then there is a mechanism for changing the spin of another particle after the first is measured, a mechanism which communicates the change of spin faster than the speed of light? Bohm's interpretation says that the whole universe is entangled and that the universal wavefunction is modified by the whole universe (and effects can travel faster than the speed of light)? but this doesn't break causality nor the rules of special relativity. The Copenhagen interpretation says that "observing" the spin of the first photon breaks the entanglement and the second photon must collapse into a given state? It gets around the "observation" problem, by saying that every time a wavefunction collapses, other universes are set up in which every possible outcome has its own universe? Have I understood this problem correctly? I know that the philosophy of quantum mechanics is a big topic and that's why I prefer to avoid it completely (shut up and calculate has gotten me through exams). However, several popular science articles confuse the hell out of me. This one for example: http://www.popsci.com/science/article/2010-03/computer-processes-faster-speed-light This entanglement thing looks, to me, like simple interference effects of two particles (young's slit or whatever). The article states that putting the "computer" in a medium rich in electrons will increase the speed of light. This sounds like anomalous dispersion in a metal/plasma (leading to superluminal phase velocity), but I can't be sure that that's all it is without a better understanding. Following links gets you to the original paper (it's free access): http://arxiv.org/abs/1003.1238 Cheers all!