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In 1935, Albert Einstein, together with Boris Podolsky and Nathan Rosen (hereafter referred to as EPR) published a now-famous physics paper entitled, "Can Quantum Mechanical Description of Physical Reality be Considered Complete?"
4 It pointed out that quantum theory (which they found very aesthetically unsatisfying), predicted that under certain conditions, photons sent off in opposite directions at the speed of light might still have a connection with each other. Einstein was concerned that this correlation between photons traveling away from each other, which he described as "ghostly action-at-a-distance," would allow the possibility of messages to be sent faster than the speed of light. Message sending could occur if we could make changes in a beam of photons coming toward us, and observe reliable corresponding changes in another beam traveling away from us. According to relativity theory, it is impossible for an informational connection to be maintained between two points that are receding from each other at the speed of light. Einstein therefore concluded that there must be something fundamentally wrong with quantum theory. |
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In 1964, physicist John Bell at the European Organization for Nuclear Research (CERN) proved the far-reaching inequality theorem now known as Bell's Theorem, and rigorously described the consequences of the EPR conjecture. Bell's Theorem implied that if an EPR-type of experiment involving photons going off in opposite directions were actually carried out, then, according to Nobel prize-winning physicist Brian Josephson, "there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote."5 |
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The appropriate physics experiments testing this conjecture have now been carried out in several laboratories worldwide: by Freedman and Clauser in Berkeley in 1972, by Aspect and his colleagues in Paris in 1982, and by Gisin at the University of Geneva in 1997.6 All of these experiments show that the widely separated photons do indeed appear to be correlated with each other, even over kilometer distances. However, since they fluctuate randomly, the person at the receiving end of the system has no way to determine whether the sender did or did not change the state of the photons the receiver is presently observing. |
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