# Feynman, Richard

# FEYNMAN, RICHARD

Richard Phillips Feynman (1918–1988) was one of the most original physicists of the second half of the twentieth century. He was born on May 11, 1918, in Far Rockaway, New York. His father came to the United States from Russia when he was very young and grew up in Patchogue, Long Island. He obtained a degree in homeopathic medicine after graduating from high school but never practiced medicine. Feynman's mother was born into a well-to-do New York family and attended the Ethical Culture School but did not go to college thereafter. Feynman had a younger brother, born when Feynman was 3, who died shortly after birth. He also had a sister, Joan, who was nine years younger than Feynman.

Feynman attended both junior and senior high school in Far Rockaway and had some very competent and talented teachers for his chemistry and mathematics courses who nurtured his interest in the sciences. He entered MIT in the fall of 1935 and was immediately recognized as an unusually gifted student by all his teachers. In 1939 he went to Princeton University as a graduate student in physics and served as John Archibald Wheeler's assistant. Wheeler, who had just arrived at Princeton as a twenty-six year old assistant professor in the fall of 1938, proved to be an ideal mentor for the even younger Feynman. Full of bold and original ideas, a man who had the courage to explore any problem, Wheeler gave Feynman viewpoints and insights into physics that would prove decisive later on.

In the spring of 1942 Feynman obtained his Ph.D. and immediately thereafter started working on problems

related to the development of an atomic bomb. In 1943 he was one of the first physicists to go to Los Alamos. He was quickly identified by Hans Bethe, the head of the theoretical division, and by Robert Oppenheimer, the director of the laboratory, as one of the most valuable members of the theoretical division. He was also acknowledged by everyone to be perhaps the most versatile and imaginative member of that community of outstanding scientists. In 1944 he was made a group leader in charge of computations for the theoretical division. Feynman introduced punch-card computers to Los Alamos, and he there developed his life-long interest in computing and computers.

While at Los Alamos, Feynman accepted an appointment at Cornell University as an assistant professor and joined its department of physics in the fall of 1945. In 1951 he left Cornell to become a member of the faculty of the California Institute of Technology, and he remained there until his death from stomach cancer on February 15, 1988.

One aspect of Feynman's genius was that he could make precise what was unclear and obscure to most of his contemporaries. His doctoral dissertation and well-known 1948 *Reviews of Modern Physics* article that presented the path integral formulation of nonrelativistic quantum mechanics helped clarify and make explicit the assumptions underlying the usual quantum mechanical description of the dynamics of microscopic entities. Moreover, he did this in the very act of extending the usual formulation with a startling innovation. His reformulation of quantum mechanics and his integral over paths may well turn out to be his most profound and enduring contribution. They have deepened scientists' understanding of quantum mechanics and have significantly enlarged the number and kinds of systems that can be quantized. His path integral enriched mathematics and has provided new insights into spaces of infinite dimensions.

Feynman was awarded the Nobel Prize in Physics in 1965 for his work on quantum electrodynamics (QED). In 1948, simultaneously with Julian Schwinger and Sin-itiro Tomonaga, he showed that the divergences plaguing QED could be consistently identified and removed by a redefinition of the parameters that describe the mass and charge of the electron in the theory, a process that is called renormalization. Schwinger and Tomonaga had done this by building on the existing formulation of the theory. Feynman, on the other hand, invented a completely new diagrammatic approach that allowed the visualization of space-time processes, which in turn simplified concepts and calculations enormously and also made possible the exploration of the properties of QED to all orders of perturbation theory. Using Feynman's methods, it became possible to calculate quantum electrodynamic processes to amazing precision. Thus, the magnetic moment of the electron has been calculated to an accuracy of one part in 10^{9} and found to be in agreement with an experimental value measured to a similar accuracy.

In 1953 Feynman developed a quantum mechanical explanation of liquid helium that justified the earlier phenomenological theories of Lev Landau and Laslo Tisza. Because a ^{4}He atom has zero total spin angular momentum, it behaves as a Bose particle: the wave function describing a system of *N* helium atoms is therefore symmetrical under the exchange of any two helium atoms. The ground-state wave function of such a system is nondegenerate and everywhere positive. When in this state, the system— even when *N* is of the order 10^{23}, and the system is macroscopic—behaves as one unit. This is why helium near 0K is a superfluid, acting as if it has no viscosity. Near 0K, pressure waves are the only excitations possible in the liquid. At somewhat higher temperatures, around 0.5K, it becomes possible to form small rings of atoms that can circulate without perturbing other atoms; these are the rotons of Landau's theory. With increasing temperature, the number of rotons increases, and their interaction with one another gives rise to viscosity. An assembly of rotons behaves like a normal liquid, and this liquid moves independently of the superfluid. At a certain point, when the concentration of normal liquid becomes too large, a phase transition occurs, and the whole liquid turns normal. This was Feynman's quantum mechanical explanation of why at any given temperature helium could be regarded as a mixture of superfluid and normal liquid.

In 1956 Tsung Dao Lee and Chen Ning Yang analyzed the extensive extant data on nuclear beta decay and concluded that parity symmetry is not conserved in the weak interactions. This was soon confirmed experimentally by Chien-Shiung Wu, Ernest Ambler, Raymond W. Hayward, Dale D. Hoppes, Ralph P. Hudson, and others. Subsequent experiments further indicated that the violation of parity is the maximum possible. On the basis of these findings, Robert Marshak and George Sudarshan, and somewhat later and independently Richard Feynman and Murray Gell-Mann, postulated that only the "left-handed" part of the wave functions of the particles involved in the reaction enter in the weak interactions. Feynman and Gell-Mann further hypothesized that the weak interaction is universal, that is, that all the weak particle interactions have the same strength. This hypothesis was later corroborated by experiments.

In the late 1960s experiments at the Stanford Linear Accelerator on the scattering of high-energy electrons by protons indicated that the cross section for inelastic scattering was very large. Feynman found that he could explain the data if he assumed that the proton was made up of small, pointlike entities, which interacted elastically with electrons. He called these subnuclear entities partons. The partons were soon identified with the quarks of Gell-Mann and George Zweig. The study of quarks and their interactions, and in particular, an explanation of their confinement inside nucleons and mesons, was an important component of Feynman's research during the 1980s.

Feynman disliked pomposity and frequently made fun of pretentious and self-important people. He was always direct, forthright, and skeptical. These traits have been beautifully captured in the volume of reminiscences that Laurie Brown and John Rigden have edited and in the stories that Feynman told Ralph Leighton. His uncanny ability to get to the heart of a problem—whether in physics, applied physics, mathematics, or biology—was demonstrated repeatedly. As a member of the presidential commission that investigated the Challenger disaster, he was able to simply convey the central problem by dropping a rubber O-ring into a glass of ice water and demonstrating its shriveling. In his physics Feynman always stayed close to experiments and showed little interest in theories that could not be experimentally tested. He imparted these views to undergraduate students in his justly famous *Feyn-man Lectures on Physics* and to graduate students through his widely disseminated lecture notes for the graduate courses that he taught. His writings on physics for the interested general public, *The Character of Physical Laws* and *QED,* convey the same message.

*See also:*Quantum Electrodynamics; Quantum Field Theory; Virtual Processes

## Bibliography

Brown, L. M., ed. *Selected Papers of Richard Feynman: With Commentary* (World Scientific, River Edge, NJ, 2000).

Brown, L. M., and Rigden, J. S., eds. *Most of the Good Stuff: Memories of Richard Feynman* (American Institute of Physics, New York, 1993).

Feynman, R. P. (with R. B. Leighton and M. Sands). *The Feynman Lectures on Physics,* 3 vols. (Addison Wesley, Reading, MA, 1963).

Feynman, R. P. *The Character of Physical Laws* (MIT Press, Cambridge, MA, 1965).

Feynman, R. P. *QED: The Strange Theory of Light and Matter* (Princeton University Press, Princeton, NJ, 1985).

Feynman, R. P. (as told to Ralph Leighton), edited by E. Hutchings. *"Surely You're Joking, Mr. Feynman!": Adventures of a Curious Character* (Norton, New York, 1985).

Feynman, R. P. (as told to Ralph Leighton). *What Do YOU Care What Other People Think?: Further Adventures of a Curious Character* (Norton, New York, 1988).

Gleick, J. *Genius. The Life and Science of Richard Feynman* (Pantheon Books, New York, 1992).

Mehra, J. *The Beat of a Different Drum: the Life and Science of Richard Feynman* (Oxford University Press, New York, 1994).

Robbins, J., ed. *The Pleasure of Finding Things Out: The Best Short Works of Richard P. Feynman* (Perseus Books, Cambridge, MA, 2000).

Schweber, S. S. *QED and the Men Who Made It* (Princeton University Press, Princeton, NJ, 1994).

*Silvan S. Schweber*

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