# Freeman J. Dyson, 1993

### Citation

For his outstanding contributions to fundamental scientific knowledge in fields as diverse as physics, biology, astronomy, and mathematics; for his courageous questioning of the risks and benefits of science and technology; and for his wonderful articles and books that describe to the public how a scientist looks at the world.

### Biography

Professor Freeman Dyson's fundamental contributions to science have been at the frontier of knowledge and have set, by their originality, rigor, and relevance, a high standard of excellence. He has helped popularize science through articles in Scientific American and The New Yorker, and many widely acclaimed books for the general public. In his writings, his courageous and informed challenges to conventional approaches to science and technology have been informative to general audiences and have been the inspiration of generations of scientists. Professor Dyson began his research as a mathematician before turning his interests in 1947-48 to the exciting new developments in physics involving the theory of quantized fields. Almost immediately upon his entry into theoretical physics, Dyson wrote two papers on the foundations of quantum electrodynamics which have had a profound and lasting influence on many branches of modern theoretical physics. He proved that the equations-of-motion approach to field theory put forth by Schwinger and Tomonaga were equivalent to the diagrammatic rules put forth by Feynman. In doing so, he introduced a novel approach, which has become a standard method for deriving the Feynman rules for a given physical system. Dyson's analysis of the renormalizability of electrodynamics has become a classic of modern theoretical physics, appearing both in standard textbook treatments and providing the motivation and model for much further work on renormalizable field theories. A further important innovation was his formulation of integral equations (now called "Dyson's equations") which gave a nonperturbative meaning to the Feynman-Dyson perturbation series. These equations play an important role in the theory of many-particle systems, and find significant application in modern formulations of the theory of superconductivity.

In the years subsequent to this work in electrodynamics, Dyson made numerous lasting contributions to scattering theory in areas of analytical properties of scattering amplitudes. Another of Dyson's major interests has been statistical physics. In an important paper, Dyson brought into tractable form a problem involving the excitation spectra of disordered systems. In a series of papers, Dyson and Mehta worked out a theory of the statistical behavior of energy levels of quantum systems, and applied the theory to cases of interest in nuclear physics. Dyson's statistical work has also involved the study of magnetic systems and phase transitions. He developed a systematic theory of spin wave interactions and applied it to the study of the low temperature behavior of an ideal ferromagnet. A final and major facet of Dyson's statistical work has been his rigorous proof with Andrew Lenard of the stability of matter.