Bell, John Stewart

(1928-1990), theoretical physicist

by C. H. Llewellyn Smith, rev.

© Oxford University Press 2004 All rights reserved

Bell, John Stewart (1928-1990), theoretical physicist, was born into a protestant working-class family in Belfast on 28 July 1928, the eldest of three sons and second of four children of John Bell. The latter worked as a horse dealer, but his health was poor and after army service he had no real job, and his wife, (Elizabeth Mary) Ann Brownlee, did some casual sewing work. After leaving the Belfast Technical High School at sixteen, John Stewart Bell worked for a year as a laboratory assistant in the physics department of the Queen's University, Belfast (1944-5); his supervisors gave him physics books to read and he was able to skip a year after he entered the university in 1946. He graduated with first-class honours in experimental physics in 1948 and in mathematical physics in 1949.

Bell worked for the Atomic Energy Research Establishment (AERE) at Malvern and Harwell from 1949 to 1953 on the theory of particle accelerators; he applied Hamiltonian dynamics to develop various analytical approaches, and he discovered the 'Courant-Snyder' invariant. He spent 1953 on leave working for a PhD in Birmingham under P. T. Matthews and Rudolf Peierls. After returning to Harwell, he completed his thesis in 1956 and began to work on many body problems and quantum field theory, with particular reference to atomic nuclei. His thesis contains a proof of the profound and fundamental parity-charge conjugation-time reversal (PCT) theorem, though his discovery of this theorem had been anticipated by G. Lüders. In 1954 he married Mary, daughter of Alexander Munro Ross, a shipyard commercial manager in Glasgow; the couple had no children. They had met when both were working for AERE on accelerator theory, and they published a joint report in 1952.

In 1960 Bell moved to the theoretical studies division at the Conseil Européen de Recherches Nucléaires (CERN), the European particle physics laboratory near Geneva, Switzerland, where he remained until his death in 1990, apart from one year's leave in 1963-4 at the Stanford Linear Accelerator Center in California. His wife also joined CERN, as an accelerator physicist. He published a large number of important papers on particle physics, his contributions including articles on CP (charge conjugation-parity) violation; the discovery that, despite having a mean free path of millions of miles in matter, neutrinos are 'shadowed' in nuclei; the observation that the algebra of electroweak charges is strongly suggestive of a gauge theory; and an illuminating explanation of the upper limit on the polarization of particles in storage rings as a manifestation of interaction with the black body radiation experienced by accelerated observers. The best-known of his 'conventional' contributions was his discovery (with R. Jackiw) of the 'Alder-Bell-Jackiw' anomaly, which leads not only to constraints on models of elementary particles but also to surprising and deep connections between physics and geometry.

Bell was best-known for work on what he described as 'his hobby--the problem of quantum mechanics'. His first contribution was to demolish John von Neumann's celebrated theorem that purported to show that 'quantum mechanics would have to be objectively false in order that another description of the elementary process than the statistical one be possible'. He then showed (Bell's theorem) that certain predictions of quantum mechanics cannot be reproduced by any 'local' theory in which the results of a measurement--or experiment, as he preferred to call it--on one system are unaffected by operations on a distant system with which it interacted in the past. The subsequent verifications of these predictions were of fundamental importance.

Bell's masterly expositions of the 'rotten' state of the foundations of quantum mechanics (collected in Speakable and Unspeakable in Quantum Mechanics, 1987), in which he stressed that without a definition of a 'measurement' the predictions are in principle ambiguous, did much to shake the 'complacent' views of other physicists. He made the most important contribution to 'quantum philosophy' since the birth of quantum mechanics, though--by exposing its essential non-locality--he only deepened the fundamental mysteries of the subject. He also had a profound knowledge of the foundations of other pillars of theoretical physics, especially classical electromagnetism.

Bell's work was recognized by his election as a fellow of the Royal Society in 1972 and as a foreign honorary member of the American Academy of Arts and Sciences in 1987; the award of the Reality Foundation prize in 1982; the Dirac medal of the British Institute of Physics, an honorary DSc from Queen's University, Belfast, and an honorary ScD from Trinity College, Dublin (all in 1988); and the Dannie Heineman prize of the American Physical Society and the Hughes medal of the Royal Society in 1989.

John Bell had red hair and a beard and spoke with a lilting Ulster accent. He generally dressed informally and was a vegetarian. He and his wife were a rather private couple, but excellent company for those who got to know them. He was a brilliant writer and teacher, both in formal lectures and in private discussions, delighting in teasing out the truth by means of Socratic dialogue and paradox. He was amused by the widespread publicity that his theorem attracted, though perhaps also mildly resentful that it tended to obscure his other contributions. He enjoyed the encounters it generated with people such as the Dalai Lama, which he described in an amused and sceptical manner.

In the 1980s Bell and his wife published several joint papers on electron cooling in storage rings and quantum beam- and bremsstrahlung. Mary Bell's comments on the drafts of her husband's papers on quantum mechanics helped improve their clarity; he wrote that in them 'I see her everywhere'. John Bell died suddenly and unexpectedly of a cerebral haemorrhage in Geneva on 1 October 1990.

C. H. LLEWELLYN SMITH, rev.

Sources  
Europhysics News, 22/4 (1991)
Physics Today (Aug 1991), 82
J. Bernstein, Quantum profiles (1991)
CGPLA Eng. & Wales (1991)
private information (1996)
personal knowledge (1996)

Wealth at death  
£106,993: probate, 20 Sept 1991, CGPLA Eng. & Wales


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