Section 8.7 The Aspect Experiment
These experiments are quite hard to do. In fact, the best experimental tests of Bell's inequality to date is done not with electrons and positrons, but rather with polarization states of photons. The first definitive test was performed in the 1980s in France by the research group of Aspect, and their data came down firmly on the side of … drum roll … quantum mechanics!
Perhaps you have been holding out hope that the spin of an electron could have some precise value and that quantum mechanics was just an incomplete theory, but Bell and Aspect have ruled out that possibility! It appears that quantum mechanics is a complete theory, and quantum mechanics states really do represent the most knowledge possible about the condition of a particle. The randomness of uncertainty in quantum mechanics that we've been studying in this unit is real.