John Stewart Bell

…theorem by the Irish-born physicist John Stewart Bell. Bell began by assuming the existence of some form of hidden variable with a value that would determine whether the measured angular momentum gives a plus or minus result. He further assumed locality—namely, that measurement on one proton (i.e., the choice of…

In 1964 the Irish-born physicist John Stewart Bell devised mathematical relationships, Bell inequalities, that would be satisfied by a hidden variable theory in which measurement of one particle would not instantly affect the properties of the other particle. Clauser became interested in experimental testing of the Bell inequalities. He and…

(Ironically, Irish-born physicist John Stewart Bell demonstrated in the mid-1960s that von Neumann’s proof was flawed; Bell then fixed the proof’s shortcomings, reaffirming von Neumann’s conclusion that hidden variables were unnecessary. See also quantum mechanics: Hidden variables.)