Hidden Variables

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Einstein, Podolsky and Rosen
Upon analysis of the Copenhagen interpretation, Einstein, Podolsky and Rosen found it lacking. Basically when the three physicists looked into the mathematics of quantum mechanics they deduced that one could violate Heisenberg's Uncertainty Principle unless two quantum objects could interact with each other instantaneously, which would, in their opinion mean information is being passed between the systems at a speed greater than that of light. They argued therefore that for this paradox to be resolved the current description of quantum mechanics was incomplete and the quantum objects must have various hidden variables, or a set of rules to follow, allowing them to imitate interaction at FTL speeds.

Von Neumann tried to completely disprove the idea of hidden variables in a paper published in 1932 aptly titled ‘No Hidden Variables’. He tried to show that the empirical results you got from measure to of quantum systems disagree with predictions that one would get with hidden variables. However it was shown by Grete Hermann in 1935 that he had only disproved local hidden variables, and that non-local hidden variables were still allowed. Her paper, however was mostly ignored until John Bell, almost 30 years later gave a very similar critique regarding Von Neumann’a paper, however he provided a solid counter-example where Hermann did not.