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Bell's Theorem and Einstein's ‘Spooky Actions’ from a Simple Thought Experiment

### Abstract

In 1964 John Bell proved a theorem^{2} allowing the experimental test of whether what Einstein derided as “spooky actions at a distance” actually exist. We will see that they *do*. Bell's theorem can be displayed with a simple, nonmathematical thought experiment suitable for a physics course at *any* level. And a simple, semi‐classical derivation of the quantum theory result can be given for physics students. These entanglement phenomena are today applied in industrial laboratories and are increasingly discussed in the popular literature. Unfortunately, they are also misappropriated by the purveyors of pseudoscience, something physicists have a responsibility to address.^{3} Students can be intrigued by the quantum strangeness physics has encountered at a boundary of our discipline.

© 2010 American Association of Physics Teachers

Published online 22 January 2010