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Bell's theorem proof. Does it really proofs anything?

by 0xDEAD BEEF
Tags: bell, proof, proofs, theorem
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DevilsAvocado
#91
Dec10-10, 09:09 AM
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zonde
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Dec10-10, 09:12 AM
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What are key points how local-realism explains these experiments?
Photon experiments that test Bell (or CHSH) inequalities relay on so called fair sampling assumption.
The thing is that you don't detect all photons that leave beam splitter but only portion. Typically you have around 10% coincidence rate i.e. you discard 9/10 of detections because you don't have matching detection at the other side.
Idea of fair sampling assumption is that if you would detect them it would not change observed correlations.
So if you assume that detected sample of photons is biased then you have to conclude that photon tests don't prove non-locality.
And I would like to add that this is the only way out of the paradox consistent with local realism.

Btw there was another idea (so called "locality loophole") but it was disproved by experiment with fast switching polarizers.

And you can try to look here as well:
Loopholes in Bell test experiments

Quote Quote by 0xDEAD BEEF View Post
No! My configuration was different. It was - Bob 0, Alisa 90. Photons flying in sometimes have angle 45, so they sometimes must hit ++, --, +-, -+, BUT, we only get +- and -+.
I guess you misunderstood me. My point was that photons flying in sometimes have 45 angle and sometimes different angle.
DevilsAvocado
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Dec10-10, 09:21 AM
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DrChinese
#94
Dec10-10, 10:41 AM
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Quote Quote by 0xDEAD BEEF View Post
1. It was - Bob 0, Alisa 90. Photons flying in sometimes have angle 45, so they sometimes must hit ++, --, +-, -+, BUT, we only get +- and -+.

2. What are key points how local-realism explains these experiments?
1. If you know that the photons coming in are polarized at 45 degrees, then they cannot be polarization entangled. And you will get: ++, --, +-, -+.

2. zonde has given a pretty good answer already. This is a very complex question and the answers tend to arouse controversy. But the short answer is that NO local realistic explanation also matches QM. In the view of zonde, local realism + fair sampling can match QM experimentally. This is far from certain (but *may* be possible). What is certain is that such local realism means that a complete sample will not agree with QM. Which follows Bell's Theorem, which essentially states:

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.


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