History of quantum physics

Q.E.D.-AND THE MEN WHO MADE IT - Dyson, Feynman, Schwinger and Tomonaga [ History of Science Series (Physics) ]: Silvan S. Schweber; Universities Press, Hyderabad. Distributed by Orient Longman Ltd., 160, Anna Salai, Chennai-600002. Rs. 775.

EINSTEIN'S THEORY of relativity and quantum physics are rated as the two astounding theories of the 20th century. While the general theory of relativity is truly the best description of space-time, it is inadequate when dealing with the origin of the universe. On the other hand, quantum physics deals with the behaviour of matter at the sub-atomic level involving very high energies. At this level, as Einstein predicted, matter and energy become interchangeable, which eventually leads to the famous equation E=MC{+2}. When we try to understand what happened at the moment when the universe was the size of an atomic nucleus, we find there is an overlap of the theory of relativity and quantum physics.The book under review deals with the history of quantum physics and its offshoot, quantum or wave mechanics, particle theory and quantum electrodynamics (QED) and the scientists behind the development and evolution of quantum physics in its various dimensions. Any student of physics worth his salt never tires of reading a well-written book on this fascinating subject. Unlike the theory of relativity whose development is attributed mainly to one scientist, Einstein, quantum physics was developed over a period of time during the first half of the 20th century through contributions from many theoretical physicists. According to Dirac it will continue to undergo small changes. While the title of the book singles out names of four outstanding physicists, there are many more who contributed in good measure towards the evolution of quantum physics and its related fields.

In 1947 to be precise, it came to light that all the three had independently arrived at solutions to the problems of linking special relativity with quantum physics.It was Dyson who showed that the solutions were identical. The resulting theory came to be known as quantum electrodynamics or QED. In a sense Dyson unified the independent versions of QED, which correctly describes how electrons behave when interacting with photons and account for the Lamb shift first noticed by Lamb in the lowest energy levels of the hydrogen atom. Schweber handles all these techno-historical details elaborately in this heavy tome. Then he goes on to add that, while all these scientists are linked in one way or the other to QED, there is a common thread that is discernible in the approach followed by Feynman and Schwinger in the development of QED. As the author remarks, scientists of their calibre give us a vision of what the human brain - and what the species - is able to understand, create and accomplish.The author has proved his mettle as a good historian of science, exuding his deep understanding of science and scientists. In Dyson's words, Schweber is an absolute master of his subject. This book provides the reader a detailed account of the development of QED from the very beginning, combining the technical advances in quantum physics with a biographical sketch of the scientists who contributed to this marvellous scientific endeavour. The book ends with an epilogue where the author discusses the renormalisation theory and points out that the most substantial advances in quantum field theory achieved in the past four decades have been guided and constrained by the renormalisation principle. It is worth noting here that Paul Dirac, who fused the first version of quantum mechanics with Einstein's theory of special relativity and developed a comprehensive mathematical description of quantum theory, was very unhappy with the theory of normalisation. He thought it did no more than paper over the cracks in a flawed theory.

The author concludes the book with the remarks that whatever the future may hold in store, it is safe to assert that the theoretical advances made in the unravelling of the constitution of matter since World War II comprise one of the greatest intellectual achievements of humankind. They were based on the ground secured by the contributions of Tomonaga, Bethe, Schwinger, Feynman and Dyson to quantum field theory and the renormalisation theory in the period from 1946 to 1951.

C. V. SUBRAMANIAM

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