## Richard Phillips Feynman

**-**

## Feynman, Richard Phillips

# FEYNMAN, RICHARD PHILLIPS

(*b*. New York, New York, 11 May 1918; *d*. Los Angeles, California, 15 February 1988),

*physics*, *quantum theory*, *particle physics*, *science teaching*.

Feynman was one of the most creative and influential physicists of the twentieth century. A veteran of the Manhattan Project of World War II and a 1965 Nobel laureate in physics, he made lasting contributions across many domains, from electrodynamics and quantum theory to nuclear and particle physics, solid-state physics, and gravitation. He also became a famous public persona. Several of his popular books—including two collections of autobiographical stories, telling of his lifelong love of playing bongo drums, puzzling through scientific mysteries, and distrusting authority figures—became runaway best sellers. Over his career—cut short after a long battle with cancer—Feynman produced 125 scientific articles and books, several of which remain at the forefront of modern physics.

**Early Years** . Feynman grew up in Far Rockaway, in the Queens section of New York City. His father, Melville, who harbored an interest in science, helped inspire young Richard with trips to museums, nature walks, the purchase of an *Encyclopedia Britannica*, and more. Melville was in the garment business—he sold uniforms to police officers, postal workers, and the like—and he taught Richard never to takeformal authority too seriously; he had, after all, seen the important figures before they acquired their fancy uniforms. Melville and his wife,
Lucille Phillips, raised their two children (Richard and his younger sister, Joan) in the tradition of reformed Judaism, although religion never played a large role in Richard Feynman’s life.

Feynman raced through New York City’s public schools, teaching himself algebra and soon calculus, even inventing his own idiosyncratic notation to streamline his calculations. He entered the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, in 1935 to begin his undergraduate studies. By his sophomore year Feynman was already enrolling in graduate-level courses in theoretical physics. He soon fell in with an equally precocious friend and study partner, Theodore (Ted) Welton. Together, Feynman and Welton dived into quantum mechanics, physicists’ bizarre yet successful description of the atomic domain, and general relativity, Albert Einstein’s notoriously difficult theory of gravitation. While still an undergraduate, Feynman published a brief letter to the editor of *Physical Review* with one of his professors, Manuel Vallarta, on the scattering of cosmic rays by interstellar magnetic fields. He also worked on a senior thesis with the renowned solid-state theorist John Clarke Slater, which resulted in an article of Feynman’s own, “Forces in Molecules,” published in *Physical Review* in 1939. This work treated the problem of molecular forces from a thoroughly quantum-mechanical point of view, arriving at a simple means of calculating the energy of a molecular system that continues to guide quantum chemists.

From MIT, Feynman went to Princeton University, in New Jersey, to pursue his PhD, starting in 1939. With the United States still trapped in the Great Depression, Feynman’s father worried that his son might not be able to find a job after all his fancy schooling. Princeton also had concerns: in those days, the physics department scrutinized every applicant of Jewish background who professed a desire to study theoretical physics, fearing that the field (if not the department) already had more than its fair share—a practice that faded soon after World War II. Undaunted, Feynman began his graduate studies and immediately impressed his young mentor, John Archibald Wheeler, who had arrived at Princeton himself, as an assistant professor, only the previous year.

Together with Wheeler, Feynman explored the ins and outs of electrodynamics. Since the middle of the nineteenth century, physicists had thought about electric and magnetic forces in terms of fields—wavelike entities extended throughout space that could act on charged particles and affect their motion. Wheeler and Feynman explored a radical alternative: what if fields did not exist, and all electrodynamic interactions arose from direct forces between particles? To make their equations yield the familiar (and well-tested) results, they needed to include two different types of interactions: “retarded,” which took into account the time required for an effect to propagate from one location to another, and “advanced,” effects that arrived at their destination before they had been emitted. Wheeler and Feynman demonstrated that the latter, while certainly paradoxical, behaved in a mathematically self-consistent manner. In a related line of thinking, Wheeler and Feynman realized that positrons—the antimatter cousins to electrons, bearing the same mass but the opposite electric charge—could be thought of as electrons traveling backward in time. In both cases, Feynman pushed particles to the forefront, rather than fields, picturing the particles’ zigzagging paths through space and time—an approach that he would continue to hone throughout his career. Feynman completed his PhD in 1942 and immediately married his high school sweetheart, Arline Green-baum, over his parents’ strenuous objections. (Arline suffered from tuberculosis.)

**War Work** . War was clearly on the horizon as Feynman finished his undergraduate studies in 1939; just three months after he graduated from MIT, Germany invaded Poland and World War II broke out in Europe. A college friend of his had already joined the Army Signal Corps, and Feynman thought seriously about joining, too. As Feynman later recalled, however, the army had not yet established any means by which scientifically trained people could contribute their special skills, so he elected to begin graduate studies at Princeton rather than basic training at an army boot camp. Two years later, in the midst of his studies, the Japanese attacked Pearl Harbor and the United States entered the war. The surprise attack sent American defense efforts into high gear.

For years, a small, secret group of scientists in the United States had been studying whether it might be feasible to create a weapon using nuclear fission, the process by which large atomic nuclei can be split apart, releasing large amounts of energy. (Unbeknownst to these scientists, similar groups were also studying the issue in Great Britain, Germany, the Soviet Union, and Japan.) Immediately after Pearl Harbor, this sleepy commission was transformed into what would become the largest scientific and technical project the world had ever seen: the Manhattan Project. A young physics professor at Princeton, Robert Wilson, was among the earliest recruits for the top-secret project. He, in turn, convinced many members of the department—graduate students and faculty alike—to join him in the effort to design and build nuclear bombs. When Wilson approached Feynman with a cryptic message (no one was allowed to speak openly about the secret project), asking Feynman if he would join, the latter at first refused. A few hours later, Feynman changed his mind—the thought of Adolf Hitler acquiring nuclear weapons before the Allies did was too frightening—and so by that afternoon he was hard at work trying to figure out how to separate the fissionable variant of uranium (U-235) from the much more common species (U-238). At the age of twenty-three, he had joined the war effort.

Late in 1938 the Berlin chemists Otto Hahn and Fritz Strassmann had detected fission of uranium nuclei; the surprising effect was first explained in terms of the physics of nuclear particles by Hahn’s former colleague, theoretical physicist Lise Meitner, and her nephew, Otto Robert Frisch, while vacationing in Sweden. (Meitner, an Austrian Jew, had been forced to flee Berlin just weeks before, after the Nazis annexed Austria.) The vast majority of naturally occurring uranium has an atomic mass of 238 (92 protons and 146 neutrons). These common nuclei are quite stable. A rare isotope, however, of atomic mass 235 (92 protons but only 143 neutrons), is highly susceptible to fission. The question Wilson posed to Feynman (and, indeed, the question on many scientists’ minds by this time) was how to separate the fissionable U-235 from the garden-variety U-238. The two types of nuclei could not be separated by chemical means; in any chemical reaction, U-235 and U-238 would behave in exactly the same way. Some physical means, exploiting the tiny mass difference, was needed. Several ideas had been advanced—some called for using powerful magnets to whip the uranium nuclei around in circles, during which time the heavier nuclei would move along slightly different paths than the lighter ones; others envisioned heating a uranium gas so that the molecules containing the lighter nuclei would drift down a chamber slightly more quickly than the heavier ones, and so on. Feynman’s first assignment was to assess the theoretical feasibility of these separation procedures and to brainstorm for other possibilities.

The Manhattan Project grew quickly; by war’s end, it had incorporated more than 125,000 people working at more than thirty sites throughout the United States and Canada. Central among these were huge, top-secret factory towns set up in Oak Ridge, Tennessee, and in Hanford, Washington, and a brand-new laboratory established in Los Alamos, New Mexico. Oak Ridge specialized in separating the uranium nuclei (using, in the end, both the electromagnetic and the gaseous diffusion methods). Hanford took on a different task: building enormous nuclear reactors to turn ordinary uranium nuclei (U-238) into a still heavier and more fissionable nucleus, plutonium (Pu), which contained 94 protons and 145 neutrons. The Los Alamos laboratory worked on the design and production of fission bombs.

Feynman arrived at Los Alamos early in 1943, while the laboratory was still under construction. He joined the theoretical physics division, or T-division, led by Hans Bethe. Feynman’s job now was to figure out some way to calculate how neutrons would behave in various bomb configurations. In principle, the task seemed straightforward: a single starter neutron, if injected into a critical mass of fissionable material (such as uranium enriched with additional U-235), could trigger a chain reaction. The initiator neutron would split one uranium nucleus; among the detritus would be, on average, about two new neutrons released when the original nucleus split apart. Each of these newly released neutrons could split additional uranium nuclei, releasing more neutrons, and so on. Every time a nucleus split, it released energy as well as more neutrons (as Meitner and Frisch had first worked out). Simple in principle, the real mechanisms of neutron scattering, absorption, fission, and release proved remarkably difficult to calculate for any realistic design.

Feynman broke the problem into constituent parts: a given neutron had a certain probability to fly out of the region containing fissionable material altogether, without causing any nuclear reactions; it had a different probability to collide once with a nucleus and be absorbed, ending its usefulness; it had a still distinct probability of colliding and inducing fission; and so on. Moreover, the new neutrons released upon fission would come out with varying speeds and energies, which would affect their likelihood for undergoing various types of reactions later on. Feynman built up powerful calculational techniques to sum over all of these possibilities, a step-by-step accounting scheme that could help the physicists understand how neutrons would diffuse throughout a typical bomb assembly. He quickly impressed both the lab’s scientific director, theoretical physicist J. Robert Oppenheimer, and the T-division leader, Bethe. By early 1944 Feynman had been promoted to be a group leader within T-division, making him the youngest group leader in all of Los Alamos.

Feynman’s other main task during the war was to serve as a safety inspector for Oak Ridge. Engineers and architects at Oak Ridge had designed storage facilities for the enriched uranium. Oppenheimer deputized Feynman to inspect the Oak Ridge facilities and determine whether or not they were safe. This task, like his main job back at Los Alamos, ultimately came down to understanding how neutrons would behave in and around fissionable material. The original Oak Ridge plans looked safe until Feynman realized that any accident—a tub of enriched uranium spilling near other containers, or worse yet, a flood in one of the containment rooms, which would slow down any itinerant neutrons and make them more likely to induce fission—could lead to disastrous explosions and deadly levels of radioactivity. Although skeptical at first, the leadership at Oak Ridge heeded Feynman’s warnings and redesigned their storage facilities.

Like many other scientists at Los Alamos, Feynman often chafed at the laboratory’s military supervision. He delighted in sending coded messages back and forth with his wife, who was staying in a sanatorium for tuberculosis patients near Los Alamos, to taunt the laboratory’s censors. (Arline died in July 1945, a few days before the first test detonation of a fission bomb in the so-called Trinity test.) He also learned how to crack safes, surreptitiously testing codes to a given safe’s combination lock while its owner was distracted. Both activities provided Feynman a way to rebuff what he regarded as stifling military discipline at the laboratory.

**Quantum Theory** . As the war was ending and Allied victory looked more and more secure, physics departments across the country began jockeying to hire Feynman. In the end, he turned down several attractive offers and followed his wartime boss, Bethe, back to Bethe’s home department at Cornell University in upstate New York. At Cornell, Feynman perfected his approach to quantum theory, melding several of his prewar insights with the more pragmatic, numbers-driven approach he had honed during the war.

One of his first tasks was to publish a long article, based on his dissertation, that presented a brand-new approach to quantum mechanics. Published in 1948 under the title, “Space-Time Approach to Non-relativistic Quantum Mechanics” in the journal *Reviews of Modern Physics*, his lengthy article focused on the “Lagrangian” function for a particle, a particular combination of kinetic and potential energy familiar from classical mechanics. The probability that a quantum object would travel from one location, *x*_{1}, at a time *t*_{1}, to some other location, *x*_{2}, at a later time *t*_{2}, Feynman showed, could be calculated by summing over—that is, integrating—all of the possible paths through space and time that connected these two end points. The contribution of each path to the total would be weighted by its classical Lagrangian function evaluated along that path; hence, the technique became known as path integrals. The main difference from the standard formalism lay not in outcomes, but in conceptual approach. Werner Heisenberg and Niels Bohr had argued vehemently during the 1920s that quantum mechanics spelled the end for any type of visualization of the atomic domain. Feynman countered with an intuitive approach, built around picturing the paths of particles through space and time.

His greatest success came on the heels of this path-integral approach. He returned to the problems of quantum electrodynamics (QED), physicists’ quantum-mechanical description of electric and magnetic forces. QED had been developed during the late 1920s and the 1930s by many of the discipline’s greatest theorists—Paul Dirac, Heisenberg, Wolfgang Pauli, Pascual Jordan, and many others. Yet as these greats had discovered, the equations of QED suffered from a dramatic sickness. When

pushed beyond the lowest approximation, they routinely broke down, yielding infinity rather than any finite predictions. After the war, Feynman tackled the problem diagrammatically. He began doodling simple space-time pictures to help keep track of the morass of separate algebraic terms that littered any given QED calculation. With a more effective accounting scheme, Feynman hoped, it would be easier to assess precisely where the equations broke down and the infinities sneaked in.

He began with the problem of electron scattering: why, on the quantum-mechanical level, two objects with the same electric charge repel each other. At the lowest order of approximation, Feynman pictured the scattering as in Figure 2. An electron came in from the lower right, while a second electron approached it from lower left. At some point, the right-side electron shot out a force-carrying particle, called a photon, or quantum, of light. Having given up some of its energy and momentum to the photon, this electron would recoil backward, much like a hunter upon firing a rifle. Hence it would veer off toward the top right. A little while later, the photon would strike into the second electron. This left-side electron would absorb the photon and its momentum, getting knocked off its course and heading toward the top left.

Feynman designed his diagram to stand in, one-forone, for the accompanying equation. For every leg of an electron’s motion, he plugged in a specific mathematical function (which gave the likelihood for an electron to travel, unperturbed, from one location to another). He plugged in a distinct function for every wavy photon line. Every “vertex,” or place within a diagram at which an electron line and a photon line met, corresponded to yet a different mathematical function (giving the likelihood for an electron to emit or absorb a photon). The diagram thus functioned, for Feynman, both as a picture of a specific physical process and as a clever mnemonic or bookkeeping device, helping him wade through QED’s famously complex calculational thickets.

The single-photon case had been easy enough to calculate even without Feynman’s diagrams. The real payoff came when considering more complicated scenarios. Quantum mechanically, the two incoming electrons could trade any number of photons back and forth—2 photons, 3 photons, 67 photons, 9,400,083 photons—and, at least in principle, every one of these possibilities had to be included in the overall calculation. The algebra became exponentially more protracted for every additional photon in the mix. Even the next-simplest level of approximation had proven tricky without Feynman’s diagrams. There were nine distinct ways the two electrons could trade just two photons back and forth. It had become frustratingly common to confuse or, worse, to omit some of these terms when working with the algebra alone. Feynman demonstrated that the various possibilities could be distinguished easily by their separate diagrams. Then their corresponding equations could be built up, piece by piece, just as the original term had been, by swapping in the appropriate mathematical expressions for every electron line, photon line, and vertex. Sure enough, when the dust settled from this extended calculation, Feynman showed that some of the infinities that had cropped up separately in several of these expressions exactly canceled each other out, leaving a finite number behind.

Feynman refined his diagrammatic approach over the course of 1947 and 1948. He first presented the new scheme at an elite, by-invitation-only conference in rural Pennsylvania in the spring of 1948—a presentation that went rather poorly. Few attendees had any idea what Feynman was doing at the blackboard, or how his strange-looking doodles fit in with the general tenets of quantum theory. Within months of the disappointing presentation, however, the younger generation of theoretical physicists began to pick up on Feynman diagrams, thanks especially to the tireless efforts of Feynman’s protégé, Freeman Dyson. Dyson had learned Feynman’s tricks while a graduate student at Cornell, and he quickly provided critical clarifications and powerful extensions. Dyson and Feynman each published a pair of influential articles on the new techniques in *Physical Review* during 1949.

Over the next two decades, Feynman’s diagrammatic approach revolutionized nearly every branch of theoretical physics, from QED to nuclear and particle physics, solid-state theory, and even gravitation. He won the 1965 Nobel Prize in Physics for this work (sharing the award with Julian Schwinger and Shin’ichiro Tomonaga). Of all Feynman’s many contributions, his diagrams have remained his greatest scientific legacy, changing the way most physicists think about the microworld.

Soon after Feynman had perfected his diagrammatic approach, the California Institute of Technology (Caltech) in Pasadena lured Feynman away from Cornell. He moved to Caltech in 1950 and remained there for the rest of his career. Two years after he moved, he married Mary Louise Bell, whom he had first met at Cornell. The relationship quickly soured, and they divorced in 1956. Among Bell’s complaints: his drumming was too loud and his head was constantly lost in calculus problems, morning, noon, and night. In 1960 Feynman married Gweneth Howarth in what proved to be a far more successful relationship: they remained together until his death in 1988.

More and more during this period, the problems that Feynman worked on came from solid-state theory. He became especially interested in liquid helium. At ordinary temperatures and pressures, helium exists as a gas; but at extremely low temperatures (a few degrees above absolute zero), helium becomes a liquid—indeed, a liquid with strange properties. Liquid helium displays superfluidity, that is, it flows with no viscosity or friction at all (unlike ordinary liquids). The phenomenon had been discovered

experimentally during the 1930s, and the great Russian theorist Lev Landau had provided a successful phenomenological description during the 1940s. Feynman brought his newest tools to bear on the problem—path integrals and Feynman diagrams—to explain superfluidity on a rigorously quantum-mechanical basis. In addition to the particle-like quantum excitations that had been studied, Feynman realized that a new quantum effect also played a role: the formation of quantum vortices. Once again his intuitive, pictorial approach proved successful.

**Particle Physics** . By the mid-1950s, Feynman’s interests had returned to his original passion: high-energy physics. Since his triumph with QED, the field had moved on to a series of new conundrums. Among them loomed the nature of nuclear forces. One type of force, dubbed the “weak force,” led nuclei to decay, as in radioactivity. Although weak-force phenomena had been well studied for decades, a big shock came in the late 1950s, when experiments confirmed some theoretical speculations about the symmetries obeyed by this nuclear force. Until that time, most physicists simply assumed that the weak force obeyed parity; that is, reversing all spatial coordinates from plus (right-handed) to minus (left-handed) and vice versa would leave the underlying physics unchanged. Not so, as new experiments confirmed in 1957: the weak force violated parity. Nature was not ambidextrous after all.

Feynman had tentatively suggested as early as 1956 that the parity symmetry had been assumed but not really proven for the weak interactions. Two young theorists, Chen-Ning Yang and Tsung-Dao Lee—both working at the fabled Institute for Advanced Study in Princeton, New Jersey—picked up on Feynman’s suggestion and showed that, indeed, neither experiment nor theory compelled the weak force to obey parity. Soon after parity violation had been confirmed experimentally, Feynman developed a first-principles description of the weak force, one that incorporated this basic handedness from the start.

By this time, nearly all physicists assumed that the weak force, much like the other fundamental forces, arose from the exchange of certain particles (just as the electromagnetic force arose, at the quantum-mechanical level, from the exchange of photons, as described by QED). The question remained: what types of particles carried the weak force, and what were the means by which these
force-carriers coupled with other types of matter? At a conference of high-energy physicists in 1957, Feynman suggested that the weak force might arise from a particular combination of couplings: part vector coupling and part axial vector, or *V - A*. (These designations refer to the behavior of the particles’ interactions under special-relativity transformations.)

Around the same time, Murray Gell-Mann— Feynman’s younger colleague and friendly rival at Caltech—arrived at the same conclusion. Rather than see his two star theorists devolve into a messy priority dispute, Caltech’s physics department chair, Robert Bacher, wisely suggested that Feynman and Gell-Mann publish an article together. Their paper, titled “Theory of the Fermi Interaction, arrived at *Physical Review* in September 1957, just days before another pair of theorists—the University of Rochester’s Robert Marshak and his graduate student, E. C. George Sudarshan—presented a similar theory at a conference in Italy. (In fact, Marshak and Sudarshan had visited with Gell-Mann in California a few months earlier, while Feynman was vacationing in Brazil.) Feynman often considered this work to be his greatest success: for the first time, he had discovered a genuine law of nature.

With the weak force conquered, many high-energy physicists turned their attention to a distinct nuclear force, known as the “strong” force. An attractive force between nuclear particles, the strong force was assumed to bind protons and neutrons together inside atomic nuclei. By the mid-1960s, Gell-Mann (and, independently, the theorist George Zweig) had postulated that protons and neutrons themselves had inner parts; Gell-Mann dubbed them quarks. With the introduction of quarks, the nature of the strong force shifted: now it was assumed to operate directly between constituent quarks, binding them together to make stable protons and neutrons; only secondarily did it give rise to attractive forces between these composite particles.

Many physicists were skeptical of the quark idea at first—was this, they wondered, just opening up an unending series of stacked Russian dolls, one layer hiding within the next? By the late 1960s a team of experimenters from Stanford University and MIT began trying to find evidence of structure within nuclear particles. They bombarded protons with high-energy electrons provided by the new, 2-kilometer-long Stanford Linear Accelerator Center. If protons were really elementary particles, then the electrons should scatter with a characteristic pattern. If, instead, some substructure lurked within the protons, the effects of these miniscule hard scattering centers should show up in the directions along which the electrons careened after scattering.

Most theorists assumed that calculating how the electrons would scatter if protons really did possess substructure would remain simply intractable. The strong force, after all, was in fact strong, and hence most of the tricks that theorists had learned from Feynman’s and others’ work on weaker forces would no longer apply. With weak forces, such as QED and the weak nuclear force, theorists could break a problem down into a long series of approximations, each more complicated step ultimately contributing less, numerically, to the overall result. Not so with the strong force.

Feynman approached the problem differently. With his characteristically visual approach, he imagined how a proton would look to a high-speed electron. From the electron’s point of view, the proton would be flattened like a pancake, thanks to the relativistic effect of length contraction. Moreover, if tiny particles did live inside protons—Feynman remained agnostic about Gell-Mann’s quarks, referring to the sub-proton particles as simply “partons,” that is, parts of a proton—then the strong forces between them would appear to act on a very slow timescale as far as the onrushing electron was concerned, owing to relativistic time dilation. So instead of seeing a horrible mess of closely packed partons teeming with the constant exchange of force-carrying particles, the electron would in effect see a handful of independent partons more or less sitting still—a far easier situation to analyze. Feynman’s parton ideas helped a young Stanford theorist, James Bjorken, finalize quantitative studies of the electrons’ scattering off of protons. Armed with Feynman’s theoretical simplification, the experimentalists’ data and Bjorken’s analyses helped convince most physicists that protons and neutrons really did contain smaller particles within them. By the mid-1970s, physicists had reconciled Feynman’s partons with Gell-Mann’s quarks.

Feynman’s other major contribution to high-energy theory concerned gravitation. Albert Einstein completed his general theory of relativity—his renowned theory of gravity—in 1915. To Einstein, gravity was nothing other than geometry: the warping of space and time accounted for how objects moved; “force” played no role at all. After a string of successes, Einstein’s elegant theory had fallen from most physicists’ attention by the 1930s, displaced by the new quantum theory, nuclear physics, and more. Feynman was among the handful of physicists who returned to the topic during the late 1950s. But where Einstein had banished force from his account of gravitation, Feynman put the notion of force—pictured, as he did the other physical forces, in terms of the exchange of force-carrying particles—center stage. In his reworked account of general relativity, Feynman replaced Einstein’s space-time curvature with a particular set of interactions among gravitons, which traveled along a perfectly smooth, flat background space-time. Though he published little on his new approach, Feynman delivered an influential course at Caltech on the topic in 1962–1963. Soon mimeographed copies of his lecture notes began to circulate widely, helping to inspire a new generation of theorists to think about gravity along these particle-physics lines. Combined with his path-integral approach, Feynman’s suggestive inroads led younger theorists, such as Bryce DeWitt, to make major progress on the topic of quantum gravity—the quest to combine general relativity with quantum mechanics in a self-consistent formulation.

**Teaching and Service** . Throughout his career, Feynman was a tremendously popular lecturer. Famously animated, he often acted out how electrons, photons, or protons would behave. During the late 1950s he was invited to teach Caltech’s large introductory physics course. In one sense, the course was a flop—even Feynman admitted that he had pitched his material at too advanced a level for the incoming undergraduates. Graduate and postdoctoral students, and even his fellow faculty, on the other hand, found his “elementary” course inspiring. With the aid of two Caltech colleagues, who transcribed his lectures for publication, his “flop” turned into one of the most renowned physics textbooks of all time, *The Feynman Lectures on Physics* (3 vols., 1963–1965). In later years, Feynman frequently gave informal lectures at nearby industrial laboratories, such as Hughes Aircraft. He also offered a popular class titled “Physics X,” open to anyone with questions about science.

Soon after *The Feynman Lectures*, Feynman began to publish a series of successful textbooks and popular books. *The Character of Physical Law* (1965), *Quantum Mechanics and Path Integrals*, with Albert R. Hibbs (1965), *Photon-Hadron Interactions* (1972), and *QED: The Strange Theory of Light and Matter* (1985). Each began as *The Feynman Lectures* had, with talks by Feynman as transcribed by colleagues. His most famous books, collections of autobiographical anecdotes and aphorisms— *“Surely You’re Joking, Mr. Feynman!”* (1985) and *What Do YOU Care What Other People Think?*(1988)—likewise stemmed from tape-recorded, bongo-playing jam sessions with his friend, Ralph Leighton (the son of one of his Caltech colleagues).

Even as his fame grew, Feynman continued to shun the kinds of worldly, political affairs in which so many of his colleagues engaged. While many of his fellow Los Alamos veterans joined the Federation of Atomic Scientists (later renamed Federation of American Scientists) soon after the war, or the Union of Concerned Scientists twenty-five years later, Feynman famously avoided such groups. Feynman even made a bet with fellow physicist Victor Weisskopf that he would forfeit ten dollars if he ever allowed himself to become saddled with any sort of professional responsibility whatsoever.

Ironically, Feynman’s fame was capped by just such a position of responsibility. In January 1986 the space shuttle *Challenger* was ripped to pieces about seventy seconds after takeoff. President Ronald Reagan convened a blue-ribbon panel to investigate the disaster, and Feynman reluctantly agreed to join. Frustrated by what he considered the bureaucratic red tape and political niceties that he thought would stymie the commission, Feynman grabbed the spotlight during televised hearings in February 1986. He had been tipped off by an insider that the accident might have stemmed from the effects of cold weather on some O-rings (rubber seals inside the shuttle’s solid-rocket boosters). Waiting for just the right moment when the television cameras were focusing on him, Feynman dipped a piece of O-ring in a glass of ice water and demonstrated how quickly it lost its elasticity. Though the investigation lumbered on for several months, the O-ring explanation finally emerged as the most probable cause. Feynman’s dramatic demonstration fixed him in much of the public’s mind as just the kind of straight-talking, iconoclastic character whom he had described in his autobiographical sketches.

His contribution to the *Challenger* investigation proved to be his last major work. Two years later he died from kidney failure, a complication arising from his long battle with cancer. He was survived by his wife, Gweneth, and their two children, Carl and Michelle.

## BIBLIOGRAPHY

*The Richard P. Feynman Papers, 1933–1988, at the Institute Archives, California Institute of Technology, Pasadena, includes Feynman’s unpublished correspondence, course and lecture notes, talks and presentations, and research notes. Laurie M. Brown, ed*., Selected Papers of Richard Feynman, with Commentary *(River Edge, NJ: World Scientific, 2000), includes a complete bibliography of Feynman’s writings*.

### WORKS BY FEYNMAN

“Forces in Molecules.” *Physical Review* 56 (1939): 340–343.

“Space-Time Approach to Non-relativistic Quantum Mechanics.” *Reviews of Modern Physics* 20 (1948):367–387.

“The Theory of Positrons.” *Physical Review* 76 (1949): 749–759.

“Space-Time Approach to Quantum Electrodynamics.” *Physical Review* 76 (1949): 769–789.

With Murray Gell-Mann. “Theory of the Fermi Interaction.” *Physical Review* 109 (1958): 193–198.

With Robert Leighton and Matthew Sands. *The Feynman Lectures on Physics*. 3 vols. Reading, MA: Addison-Wesley, 1963–1965.

*The Character of Physical Law*. Cambridge, MA: MIT Press, 1965.

*QED: The Strange Theory of Light and Matter*. Princeton, NJ: Princeton University Press, 1985.

*“Surely You’re Joking, Mr. Feynman!”: Adventures of a Curious Character*. New York: W.W. Norton, 1985.

*What Do YOU Care What Other People Think?: Further Adventures of a Curious Character*. New York: W.W. Norton, 1988.

*Selected Papers of Richard Feynman, with Commentary*. Edited by Laurie M. Brown. River Edge, NJ: World Scientific, 2000. Reprints many of Feynman’s most significant scientific articles.

*Perfectly Reasonable Deviations from the Beaten Track: The Letters of Richard P. Feynman*. Edited by Michelle Feynman. New York: Basic Books, 2005.

### OTHER SOURCES

Galison, Peter. “Feynman’s War: Modelling Weapons, Modelling Nature.” *Studies in History and Philosophy of Modern Physics*29B (1998): 391–434. A detailed analysis of Feynman’s wartime work and its influence on his later research.

Gleick, James. *Genius: The Life and Science of Richard Feynman*. New York: Pantheon, 1992. The best of several book-length biographies of Feynman, written by an award-winning science journalist.

Kaiser, David. *Drawing Theories Apart: The Dispersion of Feynman Diagrams in Postwar Physics*. Chicago: University of Chicago Press, 2005. A study of how Feynman’s diagrammatic approach entered the physics mainstream.

Schweber, Silvan S. *QED and the Men Who Made It: Dyson*, *Feynman, Schwinger, and Tomonaga*. Princeton, NJ: Princeton University Press, 1994. The most thorough analysis of Feynman’s research on electrodynamics and quantum theory.

Sykes, Christopher, ed. *No Ordinary Genius: The Illustrated Richard Feynman*. New York: W.W. Norton, 1994. Contains interviews and reminiscences from many of Feynman’s colleagues, students, and friends.

*David Kaiser*

## Richard Phillips Feynman

# Richard Phillips Feynman

The theoretical work of the American physicist Richard Phillips Feynman (1918-1988) opened up the doors to research in quantum electrodynamics. He shared the 1965 Nobel Prize in Physics.

Richard Feynman was born on May 11, 1918, in Far Rockaway, a suburb of New York City. He lived there until 1935, when he left to attend the Massachusetts Institute of Technology. After receiving a bachelor's degree in physics in 1939, he went to Princeton University, where he received a Ph.D. in 1942. While at Princeton, Feynman worked on the Manhattan Project, which eventually led him to Los Alamos, New Mexico, in 1943 to work on the atomic bomb. In 1946 he went to Cornell University, where he remained as an associate professor of theoretical physics until 1951. He spent half of that year in Brazil lecturing at the University of Rio and then became a Tolman professor of physics at the California Institute of Technology, where he stayed for more than 30 years. He had three wives and two children, Carl and Michelle.

## Solves Problems in the Theory of Quantum Electrodynamics

Feynman's primary contribution to physics was in the field of quantum electrodynamics, which is the study of the interactions of electromagnetic radiation with atoms and with fundamental particles, such as electrons. Because the equations that compose it are applicable to atomic physics, chemistry, and electromagnetism, quantum electrodynamics is one of the most useful tools in understanding physical phenomena.

The field initially grew out of work done by P. Dirac, W. Heisenberg, W. Pauli, and E. Fermi in the late 1920s.

The original theory was constructed by integrating quantum mechanics into classical electrodynamics. It provided a reasonable explanation of the dual wave-particle nature of light by explaining how it was possible for light to behave like a wave under certain conditions and like a particle (a "photon") on other occasions. Dirac in particular introduced a theory that described the behavior of an electron in accordance with both relativity and quantum mechanics. His theory brought together almost everything that was known about particle physics in the 1920s. However, when the principles behind electromagnetic interactions were brought into Dirac's equation, numerous mathematical problems arose: meaningless or infinite answers were obtained when the theory was applied to certain experimental data.

Feynman found a way to bypass, though not solve, these problems. Be redefining the existing value of the charge and the mass of the electron (a process known as "renormalization"), he managed to make the "divergent integrals" irrelevant—these were the terms in the theory which had previously led to meaningless answers. Thus, while some divergent terms still exist in quantum electrodynamics, they no longer enter the calculations of measurable quantities from theory.

The significance of Feynman's contribution is enormous. He gave the theory of quantum electrodynamics a true physical meaning as well as an experimental use. The renormalized values for the electron's charge and mass provide finite, accurate means of measuring electron properties such as magnetic moment. This theory has also made a detailed description of the fine structure of the hydrogen atom possible. It also presents a precise picture of the collisions of electrons, positrons (anti-electrons), and photons in matter.

Feynman was awarded the Nobel Prize for his work in quantum electrodynamics in 1965, together with fellow American Julian Schwinger and Shinichiro Tomonaga of Japan, both of whom had separately developed similar theories, but using different mathematical methods. Feynman's theory was especially distinct from the other two in its use of graphic models to describe the intermediate states that a changing electrodynamic system passes through. These models are known as "Feynman diagrams" and are widely used in the analysis of problems involving pair production, Compton scattering, and many other quantum-electrodynamic problems.

Feynman was fond of using visual techniques to solve problems. In addition to his Feynman diagrams, he developed a method of analyzing MASER (microwave amplification by stimulated emission of radiation) devices that relies heavily on creating accurate pictorial representations of the interactions involved. A MASER device is one that uses the natural oscillations of molecules to generate or amplify signals in the microwave region of the electromagnetic spectrum; they are used in radios and amplifiers, among other things. Feynman's method for analyzing these devices greatly simplified and shortened the solutions, as well as brought out the important features of the device much more rapidly.

Feynman also worked on the theory of liquid helium, supporting the work of the Russian physicist L. D. Landau. Landau had shown that below a certain temperature the properties of liquid helium were similar to those of a mixture of two fluids; this is known as the two-fluid model. Feynman showed that a roton, which is a quantity of rotational motion that can be found in liquid helium, is the quantum mechanical equivalent of a rapidly spinning ring whose diameter is almost equal to the distance between the helium atoms in the liquid. This discovery gave Landau's theory a foundation in atomic theory.

## Contributes to Knowledge of Quarks

Richard Feynman did work in many other areas of physics, including important work on the theory of Beta-decay, a process whereby the nucleus of a radioactive atom emits an electron, thereby transforming into a different atom with a different atomic number. His interest in the weak nuclear force—which is the force that makes the process of radioactive decay possible—led Feynman and American physicist Murray Gell-Mann to the supposition that the emission of beta-particles from radioactive nuclei acts as the chief agitator in the decay process. As James Gleick explained in *Genius,* Feynman also contributed to a "theory of partons, hypothetical hard particles inside the atom's nucleus, that helped produce the modern understanding of quarks." Quarks are the most elementary subatomic particles.

Feynman wrote many theoretical physics books which are in use in universities around the country, as well as a series entitled Feynman's Lectures in Physics, which he put together based on several terms of physics lectures he gave at the California Institute of Technology in 1965. The lectures presented a completely revolutionary approach to teaching university physics, providing a valuable resource to all physics majors. He also dabbled in many areas outside of physics, including drumming and drawing.

Feynman received the Albert Einstein Award in 1954, and he was warded the Niels Bohr International Gold Medal in 1973. He was a member of the National Academy of Science and a foreign member of the Royal Society in London.

## Explains Why the Shuttle Exploded

In January 1986, the space shuttle *Challenge* rexploded above Cape Kennedy, Florida. Feynman was named to the 12-member special (Rogers) commission that investigated the accident. When public hearings began in February, the discussion quickly turned toward the effect of cold temperatures on O-rings. These rubber rings seal the joints of the solid rocket boosters on either side of the large external tank that holds the liquid oxygen and hydrogen fuel for the shuttle. Using a glass of ice water, Feynman demonstrated how slowly the O-ring regained its original shape when it was cold. Because of the O-ring's slow reaction time, hot gases had escaped, eroded the ring, and burned a hole in the side of the right solid rocket booster, ultimately causing the explosion of the space craft.

In October 1979, Feynman was diagnosed with Myxoid liposarcoma, a rare cancer that affects the soft tissues of the body. The tumor from the cancer weighed six pounds and was located in the back of his abdomen, where it destroyed his left kidney. Feynman was diagnosed with another cancerous abdominal tumor in October 1987 and died of complications on February 19, 1988.

## Further Reading

Feynman wrote two volumes of autobiographical sketches. *Surely You're Joking, Mr. Feynman"* (1985) is a collection of anecdotes that gives the reader an excellent sense of Feynman's personality. This was followed by *What Do You Care What Other People Think? Further Adventures of a Curious Character* (1988). A short biography of him and a slightly more detailed description of the work that led him to the Nobel Prize can be found in *Nobel Prizes 1965,* published by the Nobel Foundation. The physicist Freeman Dyson's autobiography, *Disturbing the Universe* (1979), tells about Feynman's method of work. An explanation of elementary particle and quantum physics, including Feynman diagrams, can be found in Douglas C. Gianocoli's *Physics* (1980). In *Genius: The Life and Science of Richard Feynman,* James Gleick describes both the nature of the problems with which Feynman dealt and also the ways in which Feynman's solutions differed form those of other physicists. David L. and Judith R. Goodstein describe one of his solutions in *Feynman's Lost Lecture: The Motion of Planets Around the Sun* (1996).

## Additional Sources

Gribbin, John and Mary Gribbin, *Richard Feynman: A Life in Science* (1997).

Jagdish Mehra, *The Beat of a Different Drum: The Life and Science of Richard Feynman.* Oxford University Press, 1994. □

## Feynman, Richard Phillips

# FEYNMAN, Richard Phillips

(*b.* 11 May 1918 in Queens, New York; *d.* 15 February 1988 in Los Angeles, California), charismatic Nobel Prize–winning theoretical physicist who made important contributions to all phases of modern nuclear physics and helped to popularize science in the 1960s.

Feynman was one of three children born to Melville Arthur Feynman, a sales manager for a uniform company, and Lucille (Phillips) Feynman, a homemaker. He was a precocious student, winning a citywide mathematics contest in 1936 during his senior year at Far Rockaway High School and publishing an article, "Forces in Molecules,"
in the *Physical Review* while still an undergraduate at the Massachusetts Institute of Technology (MIT) in Cambridge. In 1939 he graduated from MIT with a B.Sc. (Honors) in physics.

Feynman earned his Ph.D. in theoretical physics in 1942 at Princeton University in New Jersey, writing a dissertation that examined the relationship of quantum mechanics to classical electrodynamics—the germ of his later Nobel Prize work. As a result of this research, he was drafted into working on the atomic bomb at Los Alamos, New Mexico, as part of the Manhattan Project. (Feynman was excused from compulsory military service during World War II because he failed the psychiatric part of the inductee's exam.) Working as a group leader at Los Alamos under Hans Bethe, he developed a formula to predict the yield of the untested weapon, and was present at the first detonation on 16 July 1945 at Alamogordo, New Mexico.

After the war ended, Feynman joined Bethe at Cornell University in Ithaca, New York, for five years. After what would prove to be a seminal year teaching in Rio de Janeiro, Brazil, Feynman in 1952 joined the faculty of the California Institute of Technology (Cal Tech) in Pasadena, where he spent the rest of his career as the Richard Chase Tolman Professor of Theoretical Physics. During these productive early years, Feynman developed the theory of quantum electrodynamics (QED). He was motivated by a series of conferences held in 1947 to 1949, and by a sense of competition between his own vision and that of Julian Schwinger, a Harvard physicist with whom he ultimately shared the Nobel Prize in 1965 (along with Shin-ichiro Tomonaga, who reached the same results independently just afterward). Feynman developed not only a method to "renormalize" (redefine) the competing models of classical and quantum physics, but also a method to diagram the resulting interactions of particles, known as "Feynman diagrams," and hence to compute their exact numerical value. There followed a string of triumphs: in 1957 he and Murray Gell-Mann published a brilliant paper on the "Fermi interaction," which resolved many outstanding issues concerning the so-called weak interaction of particles; his work on liquid helium the next year led directly to the successful development of superconductivity.

Feynman was not only a renowned theoretician, but also a superb lecturer. When he was asked to develop Cal Tech's new freshman physics course in 1960, he spent three years devising *The Feynman Lectures on Physics* (1963), which was still in print almost four decades later. Feynman's pedagogical persona—informal, humorous, as bedded in concrete experimental data as anything so theoretical could be—inspired three decades of students and set a new tone for physics instruction around the world. It also motivated Feynman to publish a series of books, including *Theory of Fundamental Processes* (1961) and *The Character of Physical Law* (1965), that were major factors in the popularization of science that began in the 1960s.

Feynman married his childhood sweetheart, Arline H. Greenbaum, in June 1942; she died of tuberculosis in July 1945. On 28 June 1952 he married Mary Louise Bell; the marriage was doomed from the start, since she wanted him to wear a suit and tie to work—this of a man whose father had raised him to distrust any kind of uniform. The marriage lasted less than four years, ending in divorce in 1956. Finally, while lecturing at CERN (the European Center for Nuclear Research) in Switzerland, Feynman met a young Englishwoman, Gweneth Howarth. He sponsored her immigration to the United States and married her on 24 September 1960; they had a son in 1962 and adopted a daughter in 1968. Thus the 1960s were marked for Feynman by his first true experience of domesticity. It is probably not coincidental that during this same period he took up art, becoming an accomplished sketch portraitist and a master of the samba drums.

Feynman's research work took a back seat to more pressing demands for much of the 1960s. This drought ended with a breakthrough in 1967, when Feynman read a book about the struggles of James Watson, a codiscoverer of DNA's structure, and wrote on a memo pad, "DISREGARD." He had been diligently reading all of the literature of modern physics, becoming caught up in the power struggles and theoretical battles, and had forgotten to trust his idiosyncratic instincts and methods. Now primed for another triumph, in 1968 Feynman developed a new model of proton collisions, based on theoretical entities called "partons"; his model allowed teams at the Stanford Linear Accelerator Center and at CERN to pursue research into quarks (key subatomic particles) that led them to two Nobel Prizes. This contribution to the theory of the strong interaction of particles made Feynman the only twentieth-century physicist to achieve breakthroughs in all three major areas of modern physics: electromagnetic forces, weak interactive forces, and strong interactions.

Eschewing retirement, Feynman continued working through the 1970s and 1980s. In February 1986 Feynman again earned public recognition when he was called in to help determine the cause of the *Challenger* space shuttle disaster of 28 January 1986. Using a dramatic demonstration that could have been drawn from his freshman course, Feynman showed the commission—and a huge television audience—exactly what happens when a rubber O-ring is subjected to freezing temperatures, and how this result led to the *Challenger* explosion. After suffering from recurring bouts of stomach cancer for ten years, Feynman finally succumbed to the disease in 1988. He is buried in Mountain View Cemetery in Altadena, California.

Feynman was one of the great theoretical physicists of the twentieth century. He worked on the development of the atomic bomb, made crucial contributions to the theory of superconductivity, created a method for diagraming the actions of subatomic particles, and won the Nobel Prize for his QED theory. As a professor, Feynman inspired students for three decades and wrote an enduring physics textbook. It is little wonder that one of his biographies is entitled, simply, "genius."

Feynman wrote two volumes of personal memoirs, *Surely You're Joking, Mr. Feynman!: Adventures of a Curious Character* (1985), and *What Do YOU Care What Other People Think?: Further Adventures of a Curious Character* (1988). His autobiography, with Christopher Sykes, is *No Ordinary Genius: The Illustrated Richard Feynman* (1994). Biographies include James Gleick, *Genius: The Life and Science of Richard Feynman* (1992); Jagdish Mehra, *The Beat of a Different Drum: The Life and Science of Richard Feynman* (1994); and John and Mary Gribbin, *Richard Feynman: A Life in Science* (1997). Obituaries are in the *New York Times* (17 Feb. 1988) and *Scientific American* (June 1988).

Hartley S. Spatt

## Feynman, Richard Phillips

# FEYNMAN, RICHARD PHILLIPS

**FEYNMAN, RICHARD PHILLIPS** (1918–1988), U.S. theoretical physicist. Born in New York City, Feynman was the son of an immigrant garment salesman and frustrated scientist whose curiosity and understanding of natural phenomena was a lifelong inspiration to his son. Educated at Massachusetts Institute of Technology (B.S. 1939; he had originally preferred Columbia but was apparently kept out by the Jewish quota) and Princeton (Ph.D. 1942), Feynman worked on the Manhattan (atomic bomb) Project from 1942 to 1946 in Princeton and at Los Alamos, New Mexico, where he was a computational group leader. He taught physics at Cornell University from 1946 to 1950 and at the California Institute of Technology from 1951 until his death.

Feynman won the Nobel Prize for physics in 1965 (jointly, with Julian Schwinger and Shinichiro Tomonaga) for the fundamental theoretical work that led to the development of quantum electrodynamics (from the quantum mechanics of the 1920s and 1930s). In the course of this work he also developed "Feynman diagrams," a widely used visual analytical technique. He also did important work on superconductivity and, in collaboration with his Cal Tech colleague (and rival) Murray *Gell-Mann, on quarks and other subatomic particles.

Near the end of his life Feynman served on the commission investigating the *Challenger* space shuttle disaster in 1986, creating a public sensation when he conducted, at a public hearing, a simple experiment that revealed the cause of the explosion. He also exposed the institutional management deficiencies that had made the disaster possible.

Feynman was early recognized as one of the most brilliant physicists of his generation and was widely respected as a teacher as well. His published lectures on physics are regarded as classics. He also had a reputation as a "character" – he was famous for his bongo drumming, his womanizing, and his general unconventional demeanor – and for his extreme individualism (said Gell-Mann, "I found that he had difficulty thinking in terms of 'us'"). In addition to publications in journals, he was the author of several popular books. Among his published works, both professional (mainly transcribed and edited lectures) and popular, are *The Theory of Fundamental Processes* (1961), *Quantum Electrodynamics* (1961), *The Feynman Lectures on Physics* (3 vols., 1963–65, with Robert B. Leighton and Matthew Sands), *The Character of Physical Law* (1965), *Quantum Mechanics and Path Integrals* (1965, with A.R. Hibbs), *Photon-Hadron Interactions* (1972), *qed: The Strange Theory of Light and Matter* (1985), "*Surely You're Joking, Mr. Feynman!": Adventures of a Curious Character* (1985, with Ralph Leighton), *Elementary Particles and the Laws of Physics: the 1986 Dirac Memorial Lecture* (1987, with Steven *Weinberg), and "*What Do You Care What Other People Think?": Further Adventures of a Curious Character* (1988, with Ralph Leighton). A biography, *Genius: The Life and Science of Richard Feynman* (1992, by James Gleick);*Selected Papers of Richard Feynman, with Commentary* (2000, edited by Laurie M. Brown); and a collection of letters, *Perfectly Reasonable Deviations from the Beaten Track* (2005, edited by his daughter Michelle Feynman), have been published. Feynman's life has inspired countless memoirs, a film, and two plays.

[Drew Silver (2^{nd} ed.)]

## Feynman, Richard Phillips

**Feynman, Richard Phillips** (1918–88) US theoretical physicist. He worked on the Manhattan Project to develop the atomic bomb. An inspiring teacher and orator, Feynman was professor of theoretical physics (1950–88) at the California Institute of Technology. In 1949, he introduced a graphic technique (*Feynman diagrams*) for illustrating the electromagnetic interactions between elementary particles. In 1957, Feynman and Murray Gell-Mann proposed the theory of weak nuclear force. He shared the 1965 Nobel Prize in physics for his part in the development of quantum electrodynamics **(QED)**. In 1986, he was a member of the committee that investigated the *Challenger* space-shuttle disaster.

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