Richard Phillips Feynman



American physicist


Birth                   May 11, 1918

Death                   February 15, 1988


Place of Birth                   New York City


Known for                   Developing the theory of quantum electrodynamics, and helping to create the first nuclear bomb



Career                   1939 Completed his B.S. in physics at the Massachusetts Institute of Technology


                   1942 Received his Ph.D. in physics from Princeton University for work in quantum electrodynamics


                   1942-1945 Worked with the Manhattan Project to develop the nuclear bomb


                   1945-1950 Taught physics at Cornell University


                   1950 Became a professor at the California Institute of Technology


                   1963 Published the first of his Lectures on Physics


                   1965 Won the Nobel Prize in physics for his work in quantum electrodynamics, which he shared with Julian S. Schwinger and Shin'chirō Tomonaga



Did You Know                   Bongo-drum playing was one of Feynman's favorite hobbies.


                   Feynman was renowned for his dynamic teaching methods. His published lectures on physics continue to be a popular resource for college students.


                   Feynman was a member of the committee that investigated the Challenger space shuttle explosion.







Feynman, Richard Phillips



Feynman, Richard Phillips (1918–1988), American physicist and Nobel laureate. Feynman shared the 1965 Nobel Prize in physics for his role in the development of the theory of quantum electrodynamics, the study of the interaction of light with atoms and their electrons. He also made important contributions to the theory of quarks (particles that make up elementary particles such as protons and electrons) and superfluidity (a state of matter in which a substance flows with no resistance). He created a method of mapping out interactions between elementary particles that became a standard way of representing particle interactions and is now known as Feynman diagrams. Feynman was a noted teacher, a notorious practical joker, and one of the most colorful characters in physics.


Feynman was born in New York City. As a child he was fascinated by mathematics and electronics and became known in his neighborhood as “the boy who fixes radios by thinking.” He graduated with a bachelor’s degree in physics from the Massachusetts Institute of Technology (MIT) in 1939 and obtained a Ph.D. degree in physics from Princeton University in 1942. His advisor was John Wheeler, and his thesis, “A Principle of Least Action in Quantum Mechanics,” was typical of his use of basic principles to solve fundamental problems.


During World War II (1939-1945) Feynman worked at what would become Los Alamos National Laboratory in central New Mexico, where the first nuclear weapons were being designed and tested. Feynman was in charge of a group responsible for problems involving large-scale computations (carried out by hand or with rudimentary calculators) to predict the behavior of neutrons in atomic explosions.


After the war Feynman moved to Cornell University, where German-born American physicist Hans Bethe was building an impressive school of theoretical physicists. Feynman continued developing his own approach to quantum electrodynamics (QED) at Cornell and then at the California Institute of Technology (Caltech), where he moved in 1950.


Feynman shared the 1965 Nobel Prize in physics with American physicist Julian Schwinger and Japanese physicist Tomonaga Shin’ichirō for his work on QED. Each of the three had independently developed methods for calculating the interaction between electrons, positrons (particles with the same mass as electrons but opposite in charge) and photons (packets of light energy). The three approaches were fundamentally the same, and QED remains the most accurate physical theory known. In Feynman's space–time approach, he represented physical processes with collections of diagrams showing how particles moved from one point in space and time to another. Feynman had rules for calculating the probability associated with each diagram, and he added the probabilities of all the diagrams to give the probability of the physical process itself.


Feynman wrote only 37 research papers in his career (a remarkably small number for such a prolific researcher), but many consider the two discoveries he made at Caltech, superfluidity and the prediction of quarks, were also worthy of the Nobel Prize. Feynman developed the theory of superfluidity (the flow of a liquid without resistance) in liquid helium in the early 1950s. Feynman worked on the weak interaction, the strong force, and the composition of neutrons and protons later in the 1950s. The weak interaction is the force that causes slow nuclear reactions such as beta decay (the emission of electrons or positrons by radioactive substances). Feynman studied the weak interaction with American physicist Murray Gell-Mann. The strong force is the short-range force that holds the nucleus of an atom together. Feynman’s studies of the weak interaction and the strong force led him to believe that the proton and neutron were composed of even smaller particles. Both particles are now known to be composed of quarks.


The written version of a series of undergraduate lectures given by Feynman at Caltech, The Feynman Lectures on Physics (three volumes with Robert Leighton and Matthew Sands, 1963), quickly became a standard reference in physics. At the front of the lectures Feynman is shown indulging in one of his favorite pastimes, playing the bongo drum. Painting was another hobby. In 1986 Feynman was appointed to the Rogers Commission, which investigated the Challenger disaster—the explosion aboard the space shuttle Challenger that killed seven astronauts in 1986. In front of television cameras, he demonstrated how the failure of a rubber O-ring seal, caused by the cold, was responsible for the disaster. Feynman wrote several popular collections of anecdotes about his life, including “Surely You’re Joking Mr. Feynman” (with Ralph Leighton and Edward Hutchings, 1984) and What do YOU Care What Other People Think? (with Ralph Leighton, 1988).



Microsoft ® Encarta ® Reference Library 2003. © 1993-2002 Microsoft Corporation. All rights reserved.







Feynman, Richard P.




born May 11, 1918, New York, N.Y., U.S.

died Feb. 15, 1988, Los Angeles, Calif.





in full Richard Phillips Feynman American theoretical physicist who was probably the most brilliant, influential, and iconoclastic figure in his field in the post-World War II era.



Feynman remade quantum electrodynamics—the theory of the interaction between light and matter—and thus altered the way science understands the nature of waves and particles. He was co-awarded the Nobel Prize for Physics in 1965 for this work, which tied together in an experimentally perfect package all the varied phenomena at work in light, radio, electricity, and magnetism. The other co winners of the Nobel Prize, Julian S. Schwinger of the United States and Tomonaga Shin'ichirx of Japan, had independently created equivalent theories, but it was Feynman's that proved the most original and far-reaching. The problem-solving tools that he invented—including pictorial representations of particle interactions known as Feynman diagrams—permeated many areas of theoretical physics in the second half of the 20th century.



Born in the Far Rockaway section of New York City, Feynman was the descendant of Russian and Polish Jews who had immigrated to the United States late in the 19th century. He studied physics at the Massachusetts Institute of Technology, where his undergraduate thesis (1939) proposed an original and enduring approach to calculating forces in molecules. Feynman received his doctorate at Princeton University in 1942. At Princeton, with his adviser, John Archibald Wheeler, he developed an approach to quantum mechanics governed by the principle of least action. This approach replaced the wave-oriented electromagnetic picture developed by James Clerk Maxwell with one based entirely on particle interactions mapped in space and time. In effect, Feynman's method calculated the probabilities of all the possible paths a particle could take in going from one point to another.



During World War II Feynman was recruited to serve as a staff member of the U.S. atomic bomb project at Princeton University (1941–42) and then at the new secret laboratory at Los Alamos, N.M. (1943–45). At Los Alamos he became the youngest group leader in the theoretical division of the Manhattan Project. With the head of that division, Hans Bethe, he devised the formula for predicting the energy yield of a nuclear explosive. Feynman also took charge of the project's primitive computing effort, using a hybrid of new calculating machines and human workers to try to process the vast amounts of numerical computation required by the project. He observed the first detonation of an atomic bomb on July 16, 1945, at Alamogordo, N.M., and, though his initial reaction was euphoric, he later felt anxiety about the force he and his colleagues had helped unleash on the world.



At war's end Feynman became an associate professor at Cornell University (1945–50) and returned to studying the fundamental issues of quantum electrodynamics. Inthe years that followed, his vision of particle interaction kept returning to the forefront of physics as scientists explored esoteric new domains at the subatomic level. In 1950 he became professor of theoretical physics at the California Institute of Technology (Caltech), where he remained the rest of his career.



Five particular achievements of Feynman stand out as crucial to the development of modern physics. First, and most important, is his work in correcting the inaccuracies of earlier formulations of quantum electrodynamics, the theory that explains the interactions between electromagnetic radiation (photons) and charged subatomic particles such as electrons and positrons (anti electrons). By 1948 Feynman completed this reconstruction of a large part of quantum mechanics and electrodynamics and resolved the meaningless results that the old quantum electrodynamic theory sometimes produced. Second, he introduced simple diagrams, now called Feynman diagrams, that are easily visualized graphic analogues of the complicated mathematical expressions needed to describe the behaviour of systems of interacting particles. This work greatly simplified some of the calculations used to observe and predict such interactions. (See also Feynman diagram; quantum electrodynamics.)



In the early 1950s Feynman provided a quantum-mechanical explanation for the Soviet physicist Lev D. Landau's theory of superfluidity—i.e., the strange, frictionless behaviour of liquid helium at temperatures near absolute zero. In 1958 he and the American physicist Murray Gell-Mann devised a theory that accounted for most of the phenomena associated with the weak force, which is the force at work in radioactive decay. Their theory, which turns on the asymmetrical “handedness” of particle spin, proved particularly fruitful in modern particle physics. And finally, in 1968, while working with experimenters at the Stanford Linear Accelerator on the scattering of high-energy electrons by protons, Feynman invented a theory of “partons,” or hypothetical hard particles inside the nucleus of the atom, that helped lead to the modern understanding of quarks.



Feynman's stature among physicists transcended the sum of even his sizable contributions to the field. His bold and colourful personality, unencumbered by false dignity or notions of excessive self-importance, seemed to announce: “Here is an unconventional mind.” He was a master calculator who could create a dramatic impression in a group of scientists by slashing through a difficult numerical problem. His purely intellectual reputation became a part of the scenery of modern science. Feynman diagrams, Feynman integrals, and Feynman rules joined Feynman stories in the everyday conversation of physicists. They would say of a promising young colleague, “He's no Feynman, but . . .” His fellow physicists envied his flashes of inspiration and admired him for other qualities as well: a faith in nature's simple truths, a skepticism about official wisdom, and an impatience with mediocrity.



Feynman's lectures at Caltech evolved into the books Quantum Electrodynamics (1961) and The Theory of Fundamental Processes (1961). In 1961 he began reorganizing and teaching the introductory physics course at Caltech; the result, published as The Feynman Lectures on Physics, 3 vol. (1963–65), became a classic textbook. Feynman's views on quantum mechanics, scientific method, the relations between science and religion, and the role of beauty and uncertainty in scientific knowledge are expressed in two models of science writing, again distilled from lectures: The Character of Physical Law (1965) and QED: The Strange Theory of Light and Matter (1985).



James Gleick





Additional reading




James Gleick, Genius: The Life and Science of Richard Feynman (1992), is a popular biography. Silvan S. Schweber, QED and the Men Who Made It (1994), is a technical study of Feynman's work.







Article mentioning Feynman discoveries



The Experiment with Two Holes



Nobody really understands quantum physics, says scientist John Gribbin. Even to advanced physicists, the question of why subatomic particles can act as both waves and particles is still a puzzle. But the classic 19th-century “experiment with two holes” is still the best way to illustrate how they behave that way. Gribbin’s simple explanation of the experiment illuminates why quantum mechanics, which provides the basis for modern physics and the scientific understanding of the structure of matter, still challenges common sense.



The Experiment with Two Holes

By John Gribbin


Quantum physics is both mysterious and exciting. It describes a world of subatomic particles where entities such as electrons can be both particle and wave at the same time, and sometimes behave as if they are in two places at once. Much of quantum physics runs counter to everyday common sense. And yet, quantum physics underpins a great deal of modern science, from chemistry and molecular biology to lasers, semiconductors, and nuclear power. In addition, of course, it is at the heart of our understanding of the way forces operate between electrically charged particles, or the forces that operate between quarks.


Some people find it frustrating that they cannot make sense of quantum physics, and worry that somehow they are missing the point of what it is all about. But if so they are in good company, and they can take comfort from the words of Richard Feynman, the greatest physicist since Einstein, who said in his book The Character of Physical Law, “I think I can safely say that nobody understands quantum mechanics”—and this from a man who won the Nobel Prize for his work in the subject. You shouldn't try to understand how quantum physics works, Feynman taught us. All you can do is get a picture of what is going on. And the best way to get that picture is from what he called “the experiment with two holes,” but which most textbooks refer to as Young's double-slit experiment. This, said Feynman on page 1 of the volume of his famous Lectures on Physics devoted to quantum physics, is “a phenomenon which is impossible, absolutely impossible, to explain in any classical [that is, common sense] way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery … the basic peculiarities of all of quantum mechanics.” If you can come to terms with the experiment with two holes, then you can come to terms with quantum physics, since every other quantum mystery can always be put in context by saying, “You remember the experiment with two holes? It's the same thing again.”


Thomas Young, who gave the experiment its more formal name, was a British physicist who worked in the early 19th century. His version of the experiment involved light, and for a hundred years or so it was seen as proof that light is a wave. The experiment may be familiar from school days. One pure color of light (which is usually interpreted as meaning a single wavelength of light) is shone through a hole in a screen, and on to another screen in which there are two holes, or sometimes two long, narrow slits. Two sets of light waves spread out, one from each of the holes, like ripples on a pond, and (just like two sets of ripples produced by dropping two stones into a still pond simultaneously) they interfere with one another. The result is that when the light arrives at the final screen in the experiment, it makes a characteristic pattern of light and dark stripes, called interference fringes. This is straightforward, schoolroom science, from which you can even work out the wavelength of the light involved, by measuring the spacing of the fringes. And one key feature of the interference pattern is that it is brightest at a point on a line midway between the two holes, where the two waves add together.


As Young summed up his work, in 1807, “the middle of the pattern is always light, and the bright stripes on each side are at such distances that the light coming to them from one of the apertures must have passed through a longer space than that which comes from the other by an interval which is equal to the breadth of one, two, three, or more of the supposed undulations [wavelengths], while the intervening dark spaces correspond to a difference of half a supposed undulation, of one and a half, of two and a half, or more.”


The trouble with this understanding of light emerged at the beginning of the 20th century, when the work of first Max Planck (on black body radiation) and then Albert Einstein (on the photoelectric effect) showed that light could be treated—indeed, in some circumstances had to be treated—as if it were a stream of little particles, light quanta, now known as photons.


The way particles pass through two holes in a wall is very different, in the everyday commonsense world, from the way waves behave. If you stood on one side of a wall in which there were two holes, and threw stones (or tennis balls) in the general direction of the wall, some would go through each of the holes, and they would make two piles on the other side of the wall, one behind each hole. You certainly would not get one big pile of tennis balls, or rocks, halfway between the two holes in the wall.


The discovery that light can behave like a wave or like a particle is an example of wave-particle duality. By the 1920s it was clear that electrons, which were traditionally regarded as particles, could also behave like waves, in another example of wave-particle duality. Now, we know that in the Alice-in-Wonderland-like quantum world all waves are particles, and all particles are waves. And we can summarize decades of delicate probing of this central mystery of the quantum world by describing what happens when individual quantum entities, either electrons or photons, are fired, one at a time, through the experiment with two holes.


It is important to stress that this really has been done, with both kinds of quantum entity (and even with whole atoms). This is not some sort of hypothetical thought experiment, but real physics which has been studied in laboratories. The electron version of the experiment was carried out in 1987, by Japanese researchers, and works like this.


When electrons are fired through a version of the experiment with two holes, their arrival on the other side can be recorded on a detector screen like a television screen. The special feature of this screen is that each electron makes a spot of light on the screen, and the spot stays there as other electrons arrive, each making its own spot, so that gradually they build up a pattern on the screen. Each electron leaves a “gun” on one side of the experiment as a particle. Each electron arrives at the detector on the other side as a particle, and makes one small spot on the screen. But as thousands of electrons are fired through the experiment one at a time, the pattern that builds up on the screen is the classic interference pattern associated with waves.


This is doubly mysterious. Not only are the electrons leaving and arriving as particles, but somehow travelling as waves (as if each electron passes through both holes in the experiment and interferes with itself), but they seem to “know” the past and the future as well. If thousands of electrons traveled together through the experiment, it might be easy to understand that they could jostle one another into an interference pattern. But only one electron passes through the experiment at a time, and somehow chooses its place on the screen on the other side so that the pattern that gradually builds up is the classic interference pattern. How can each electron possibly “know” its rightful place in the pattern?


And there's more. If one of the two holes is blocked off, the electrons form one blob of spots on the screen behind the remaining hole, equivalent to the pile of rocks you would get by throwing them through a hole in the wall. With the other hole open and the first one closed, you get a blob on the screen behind that hole. But with both holes open, the interference pattern emerges, with the brightest part of the pattern on the line midway between the holes. An individual electron, passing through just one hole in the experiment, seems to be aware whether or not the second hole is covered up, and to adjust its trajectory accordingly.


Don't look for the answer to that question here, or anywhere else. Remember that “nobody understands quantum mechanics.” As Feynman cautioned, “do not keep saying to yourself, if you can possibly avoid it, 'But how can it be like that?' because you will go 'down the drain' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.”


About the author: John Gribbin is visiting fellow in astronomy, University of Sussex in England, and author of In Search of Schrödinger's Cat and other books.