TR: John Bell and the Nature of Reality

[bystander]

John Bell and the Nature of Reality
Technology Review | the physics arXiv blog | 14 July 2010

Why have so few heard of one of the great heroes of modern physics?

In 1935, Einstein and his colleagues Boris Podolsky and Nathan Rosen outlined an extraordinary paradox associated with the then emerging science of quantum mechanics.

They pointed out that quantum mechanics allows two objects to be described by the same single wave function. In effect, these separate objects somehow share the same existence so that a measurement on one immediately influences the other, regardless of the distance between them.

To Einstein, Podolsky and Rosen this clearly violated special relativity which prevents the transmission of signals at superluminal speed. Something had to give.

Despite the seriousness of this situation, the EPR paradox, as it became known, was more or less ignored by physicists until relatively recently.

Today, we call the relationship between objects that share the same existence entanglement. And it is the focus of intense interest from physicists studying everything from computing and lithography to black holes and photography.

It's fair to say that while the nature of entanglement still eludes us, few physicists doubt that a better understanding will lead to hugely important insights into the nature of reality.

Many researchers have helped to turn the study of entanglement from a forgotten backwater into one of the driving forces of modern physics. But most of them would agree that one man can be credited with kickstarting this revolution.

This man was John Bell, a physicist at CERN for much of his career, who was incensed by the apparent contradictions and problems at the heart of quantum mechanics. In the early 60s, Bell laid the theoretical foundations for the experimental study of entanglement by deriving a set of inequalities that now now bear his name.



While Bell's inequalities are now mainstream, Bell was more or less ignored at the time. Now Jeremy Bernstein, a physicist and writer who knew Bell, publishes a short account of the background to Bell's work along with some interesting anecdotes about the man himself, some of which are entirely new (at least, to me). He recounts screaming arguments between Bell and his university lecturers about the nature of quantum mechanics. And says that at the time of his death in 1991, Bell had been nominated for a Nobel Prize, which he was expected to win.

That would have entirely changed Bell's legacy. He is well remembered by many working on the foundations of quantum mechanics but not well known by people in other areas. As a good example of a scientist who took on the establishment and won, that is a shame.

A Chorus of Bells | Jeremy Bernstein

• arXiv.org > physics > arXiv:1007.0769 > 05 Jul 2010

[neufer]

<<John Stewart Bell (28 June 1928 – 1 October 1990) was born in Belfast, Northern Ireland, and graduated in experimental physics at the Queen's University of Belfast, in 1948. In 1964, after a year's leave from CERN that he spent at Stanford University, the University of Wisconsin–Madison and Brandeis University, he wrote a paper entitled "On the Einstein-Podolsky-Rosen Paradox". In this work, he showed that carrying forward EPR's analysis[2] permits one to derive the famous Bell's inequality. This inequality, derived from certain assumptions, conflicts with the predictions of quantum theory.

There is some disagreement regarding what Bell's inequality — in conjunction with the EPR analysis — can be said to imply. Bell held that not only local hidden variables, but any and all local theoretical explanations must conflict with the predictions of quantum theory: "It is known that with Bohm's example of EPR correlations, involving particles with spin, there is an irreducible nonlocality." According to an alternative interpretation, not all local theories in general, but only local hidden variables theories (or "local realist" theories) have shown to be incompatible with the predictions of quantum theory.

In 1972 the first of many experiments that have shown (under the extrapolation to ideal detector efficiencies) a violation of Bell's Inequality was conducted. Bell himself concludes from these experiments that "It now seems that the non-locality is deeply rooted in quantum mechanics itself and will persist in any completion." This, according to Bell, also implied that quantum theory is not locally causal and cannot be embedded into any locally causal theory.

Bell remained interested in objective 'observer-free' quantum mechanics. He stressed that at the most fundamental level, physical theories ought not to be concerned with observables, but with 'be-ables': "The beables of the theory are those elements which might correspond to elements of reality, to things which exist. Their existence does not depend on 'observation'."He remained impressed with Bohm's hidden variables as an example of such a scheme and he attacked the more subjective alternatives such as the Copenhagen interpretation.

Bell seemed to be quite comfortable with the notion that future experiments would continue to agree with quantum mechanics and violate his inequalities. Referring to the Bell test experiments, he remarked: "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 ..."

Bell died unexpectedly of a cerebral hemorrhage in Belfast in 1990. His contribution to the issues raised by EPR was significant. Some regard him as having demonstrated the failure of local realism (local hidden variables). Bell's own interpretation is that locality itself met its demise.>>