John Bell and Bell's Theorem
Sheldon Goldstein, Roderich Tumulka, Nino Zangh�
John Stewart Bell (1928-1990), a truly deep and serious thinker, was one of the leading physi-cists of the 20th century. He became famous for his discovery that quantum mechanics impliesthat nature is nonlocal, i.e., that there are physical inuences between events that propagatefaster than light.From 1960 until his death Bell worked at CERN in Geneva on the physics of particle accel-erators, making a number of important contributions to high-energy physics and quantum eldtheory. Noteworthy was his discovery in 1969, together with Roman Jackiw, of the so-called\Bell-Jackiw-Adler anomaly (discovered independently by Stephen Adler), a mechanism ex-plaining physical e ects such as neutral pion decay (which are unexplainable on the basis of thesymmetries of the classical eld Lagrangian), in terms of an \anomalous term arising from therenormalization of quantum eld theory. Since then this mechanism has become an importantcornerstone of quantum eld theory. Another important contribution was the argument he gavein 1967 for why weak interactions should be described using a gauge theory.John Bell was one of the leading experts|perhaps the leading expert|on the foundations ofquantum mechanics. The book collecting his articles on this subject, Speakable and unspeakablein quantum mechanics, is unsurpassed for clarity and depth and it is still the best reference forwhoever wishes to learn about the eld [4].Bell strongly opposed the \Copenhagen interpretation of quantum physics, according towhich macroscopic objects, such as chairs and planets, do exist out there, but electrons andother microscopic particles do not. According to the Copenhagen view, the world is divided intotwo realms, macro and micro, \classical and \quantum, logical and contradictory|or, as Bellput it in one of his essays, into \speakable and \unspeakable. Along with Albert Einstein,Erwin Schrodinger, Louis de Broglie and !David Bohm, Bell was one of the few physicistscompelled by his conscience to reject the Copenhagen interpretation.Bell emphasized that the empirical facts of quantum physics do not at all force us to renouncerealism. There is, in fact, a realist theory (!Bohmian mechanics, also known as the de Broglie-Bohm theory) that accounts|insofar as the nonrelativistic theory is concerned|for all of thesefacts in a most elegant way. This theory describes a world in which electrons, quarks andthe like are point particles, always having positions that move in a manner dictated by thewave function. It should be taught to students, Bell insisted, as a legitimate alternative tothe prevailing orthodoxy. After GianCarlo Ghirardi, Alberto Rimini, and Tullio Weber in 1986succeeded in formulating a second kind of realist theory, Bell encouraged the further developmentof this theory as well [4, p. 201]. He thought that such a theory contained the seeds of a1
•Jan 1, 2004•1 citation