Social Scientist. v 25, no. 290-291 (July-Aug 1997) p. 68.

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Remembering Dirac

Peter Goddard (ed.), Paul Dirac, the Man and His Work, Cambridge University Press, 1998, pp.124.

In popular imagination the names of Einstein (God does not play dice!), Schrodinger (Wave equation, Cat Paradox) and Heisenberg (Uncertainty relations) are associated with the quantum revolution in the 20th century physics. Paul Adrien Maurice Dirac, one of the founders of quantum theory along with Schrodinger and Heisenberg was never well known to the public though his name is associated with one of the most important equation in quantum theory—Dirac's equation of the electron. It is possibly a measure of this lack of recognition in the public mind that it took 11 years after his death for a memorial to be put up for him in Westminister Abbey. This belated recognition of Dirac, 'probably the greatest British theoretical physicist since Newton' was found scandalous by Stephen Hawking in his memorial address on the occasion. The volume under review contains four lectures delivered to commemorate Dirac and bring out quite succinctly the relationship between Dirac's character and his scientific achievements.

Among physicists and students of physics Dirac's name and work has inspired awe for over half a century. Leopold Infeld in the early 1940s had described Dirac's book The Principles of Quantum Mechanics as the bible of modern physics and said "It is deep, simple, lucid and original. It can only be compared in its importance and maturity to Newton's Principia." At the age of around thirty he was admired as a genius and a legend. Infeld observed "His thin figure with its long hands, walking in heat and cold without overcoat or hat, was a familiar one to Cambridge students. His loneliness and shyness were famous among physicists. Only a few men could penetrate his solitude." The stories about Dirac among several generations of physicists are a legion.

Described as the purest soul among physicists by Niels Bohr, Dirac's genius consisted in obtaining unexpected results by reconciling what appeared to be irreconcilable. Two discoveries that brought in a conceptual shift of unprecedented magnitude in physics in the early part of the century were: the Theory of Relativity and Quantum Mechanics. Dirac's effort to make quantum theory compatible with relativity led to the discovery of what is known as anti-matter. Dirac's wave function posited four components two with negative and two positive energies each pair with spin up/down. The negative energy solution led to the prediction and subsequent discovery of the positron which ranks among the great triumphs of modern physics. Simi-

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