zlacker

>>qqqqqu+(OP)
Bell's theorem. It somehow proves that quantum physics is incompatible with local hidden variables, but I could never see an understandable explanation (for me at least) of just how it works.

>>lpelli+ag
The short answer is this. Suppose thread OP gave you and I a box each. Each box has a some knobs to choose some settings, and if one chooses a setting and presses the GO button, a number pops up on the screen. We go far away from each other so that, due to the finite speed of light, it takes quite a while for any information to travel between the boxes. We do this, because we don't want the boxes to communicate live, even though thread OP might have recorded the same data into the memory drive of both boxes.

Then we choose some settings and press GO and record whatever number pops up. We do this many times so we each have a nice frequency chart. Now Bell proved that if you live in a local hidden variable universe, the correlations between these numbers is upper bounded, no matter how you choose settings on the boxes. Then, he also gave a prescription for choosing the settings, such that if you live a in quantum universe, the correlations between these numbers will be higher than the upper bound.

The rest is mathematics, which cannot really be simplified without leaving the reader unsatisfied.

>>abdull+7y
So what I don't understand is, if both of us take an identical Gemalto token / Yuvikey, we can be light years apart and get the same sequences, no? Is the explanation that these will have one type of distribution vs if they had real "spooky movement at a distance" they have a clear different distribution? EDIT: what about this one: https://arxiv.org/abs/quant-ph/0301059

>>eranat+oB
The distance is part of the proof, but not really part of the mystery.

I'm going to throw out an analogy that gets at what's observed and why it's surprising, but doesn't relate to the physics of spin, momentum, position or anything that's actually under observation in these experiments.

It's as if we have a pair of dice, and I throw my die and you throw your die many times. In a classical world, if I throw a three, it has no influence on what you throw; you're equally likely to throw 1-6. But in the quantum world it's as if when I throw a one, your die still has the expected uniform distribution, but when I happen to throw a three, you're a little bit more likely to throw a three. Your die is fair if I happen to roll a one, but it's weighted if I happen to throw a three.

Back in the real world, this is the strange behavior that is observed in experiment. Schroedinger's equation predicts the probabilities perfectly. But Bell shows that it's far from intuitive.