4 ms·

So the real problem isn't that "when one is up, then the other will magically be up too." That could be accomplished with local hidden variables (e.g. shared s

by fizx 11y ago

So the real problem isn't that "when one is up, then the other will magically be up too." That could be accomplished with local hidden variables (e.g. shared seeds on a PRNG). The real problem is that when you measure A in the "up" direction, and then B in the "10 degrees east of up" direction, then B seems to know that you measured A in the "up" direction. That is to say: B's probability distribution as a function of the direction its being measured is dependent on the direction that A is measured. There's no way to construct an "A-independent" probability distribution of B's results for arbitrary directions. The probabilities won't sum to 1 and still match experimental results. It's unfortunate that "A up" therefore "B up" is a degenerate case of this reality where classicality actually works, because it leads to confusion. Also, follow the links others have provided for a more formal explanation :)

deleted 11y ago
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mkehrt 11y ago
This is the clearest explanation I have ever seen of this; thanks.
trhway 11y ago
>The probabilities won't sum to 1 and still match experimental results. exactly. The probabilities are 1 only in theory. For example theoretical Malus law over all angles would give 1. On practice - i couldn't find single photon Malus law confirmation. A slight deviation from Malus law like cutting the tail at high angles off and thus decreasing the total to below 1 (ie. when/if photons at high angles being lost disproportionally much more intensively than Malus law states) would bring the experimentally measured S to values higher than 2 while still being in the realm of local realism.
bsaul 11y ago
But then what about a partially shared seed (sharing only a few digits) ? Couldn't you imagine a hidden variable only influencing the probablity distribution, making it only more likely to see an up on both, although still keeping it partially random ?
tomp 11y ago
But doesn't this then violate "no information faster than speed of light"? I.e. You measure A at angle a, I measure B (entangled with A) at angle b, and the resulting distribution gives me some information about your angle a. If I repeat this with enough particles, I can be reasonably certain about what a is.
- fizx 11y ago
  The proof eludes me at the moment, but people have thought of this.

by fizx 11y ago

deleted 11y ago

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mkehrt 11y ago

This is the clearest explanation I have ever seen of this; thanks.

trhway 11y ago

>The probabilities won't sum to 1 and still match experimental results. exactly. The probabilities are 1 only in theory. For example theoretical Malus law over all angles would give 1. On practice - i couldn't find single photon Malus law confirmation. A slight deviation from Malus law like cutting the tail at high angles off and thus decreasing the total to below 1 (ie. when/if photons at high angles being lost disproportionally much more intensively than Malus law states) would bring the experimentally measured S to values higher than 2 while still being in the realm of local realism.

bsaul 11y ago

But then what about a partially shared seed (sharing only a few digits) ? Couldn't you imagine a hidden variable only influencing the probablity distribution, making it only more likely to see an up on both, although still keeping it partially random ?

tomp 11y ago

But doesn't this then violate "no information faster than speed of light"? I.e. You measure A at angle a, I measure B (entangled with A) at angle b, and the resulting distribution gives me some information about your angle a. If I repeat this with enough particles, I can be reasonably certain about what a is.

fizx 11y ago
The proof eludes me at the moment, but people have thought of this.