John Stewart Bell

John S. Bell (June 28 1928 - October 1 1990) was an Irish physicist.

Bell was born in Belfast, Northern Ireland.

In 1964 he derived an inequality that must be satisfied for there to be a local hidden-variable theory of quantum mechanics. He showed that von Neumann?s proof against deterministic quantum mechanics lacked rigor and that Bohm?s work got around von Neumann?s objections through the use of superluminal signalling. In 1967 the first of many experiments that have shown a violation of Bell's Inequality was conducted. The fate of local hidden-variable theories is currently generally regarded as sealed. Bell's Theorem has come to be regarded a proof that the underlying theory of the universe must be a quantum-mechanical one, although Bell's original goal was just the opposite.

Bell became a supporter of the Bohm interpretation, a nonlocal hidden-variable theory involving supraluminal signaling, calling its suppression a "scandal" within physics, and took to defending his work against those whom he perceived as distorting its meaning to favor indeterministic quantum mechanics such as the Copenhagen and Everett "many-worlds" interpretations.

It is possible, though, that the experimental results did not force him as strongly as he thought into adoption of this counterintuitive theory. Refering to the "Bell test experiments", a remark of his is frequently quoted:

"It is difficult for me to believe that quantum mechanics, working very well for currently practical set-ups, will nevertheless fail badly with improvements in counter efficiency ..." (Ref 1, page 109)

This belief ignores the facts of the "fair sampling loophole", first publicised by Philip Pearle in 1970 (Ref 2). The loophole means that increases in counter efficiency are likely to decrease the measured quantum correlation, destroying the empirical match with quantum mechanics.

Taking account of the all relevant loopholes, he might have been able to achieve his own original goal -- a local hidden-variable theory. As his theorem correctly showed, such a theory would have conflicted with quantum mechanics, but it might nevertheless have had no conflict with experiment.

For more on the history and physics of Bell's theorem, see the articles on Bell's inequality and the EPR paradox.

Bell died in Belfast.

References:

• Bell, John S, The Speakable and Unspeakable in Quantum Mechanics, Cambridge University Press 1987
• Pearle, P, Hidden-Variable Example Based upon Data Rejection, Physical Review D, 2, 1418-25 (1970)

See also:

• Bell's theorem
• EPR paradox
• CHSH Bell test
• GHZ experiment
• Quantum entanglement
• BellTestLoopholes
• Bell state