Bell experiment
Experiments on entangled pairs or triplets of photons can be used to test the notion of
physical realism. In the original Bell-type experiments, both photons of an entangled
pair have the same linear polarization for parallel polarizers. But for polarizers oriented at a
small angle with respect to each other, as shown, the same result is more often obtained for
both photons than would be permitted if polarization were a real local property of the
photons.