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I've read about Bell's inequality and Aspect's experience on quantum entanglement. However, those readings are written in academic terms and are difficult to understand. So I just want to know if my understanding is right:
2 entangled photons are emitted at the same time. The sum of their polarity equals 0 (conservation). They can either have a vertical or horizontal polarity. The photons then hit a polariser which detects the photon's polarity. The results tend to give credit to the Copenhagen Interpretation.
Does it means that when we change, let say, polariser X angle (in such that the detected polarities of the 2 photons would not have a sum of 0), the photon which is about to hit that polariser will instantly change its polarity in order that the detected polarities will give a sum of zero even though we changed the 'rules' at the last moment? If no communication FTL is possible between those 2 photons, how is one photon 'aware' of the other photon's polarity?? How's that suppose to be possible?! Am I right in my understanding? Please help me!
- Guillaume (age 25)
You've accurately described the beginning of the experiments. For further non-technical follow-up you might read D'Espagnat's article in the Nov. 1979 Scientific American, or find one of David Mermin's nice descriptions.
I don't think that it's correct to say that the results favor Copenhagen. What they do show is that, barring weird conspiracies, nature is not describable by a 'local realist' theory. There are facts about the world, e.g. connections between the possible results for those two distant spins, that cannot be expressed by any local properties. The spins 'know' that they have opposite angular momenta, but they do not actually have any particular value of angular momentum.
There's no indication of a spin changing value in response to a change in the detector because the spin doesn't have a value to begin with.
It never ceases to seem astounding that things can be this way.
(published on 12/16/09)
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