Feynman

A Luminary of Quantum Physics

Introduction

Early Education and Intellectual Development

Born in Far Rockaway, New York City, on May 11, 1918, Feynman displayed an exceptional aptitude for mathematics and science from a young age. He attended Far Rockaway High School, alongside future Nobel laureates Burton Richter and Baruch Samuel Blumberg. By the age of 15, Feynman had independently mastered trigonometry, advanced algebra, infinite series, analytic geometry, and calculus. He even explored advanced mathematical concepts like the half-derivative, developing his own notation.

Education at MIT and Princeton

Feynman’s formal education began at the Massachusetts Institute of Technology (MIT). Initially, he pursued mathematics, but he found it too abstract. He then shifted to electrical engineering, but eventually settled on physics, which he considered a balance between the abstract and the applied. As an undergraduate, he co-authored a paper on “The Scattering of Cosmic Rays by the Stars of a Galaxy” with Manuel Vallarta, published in the Physical Review. In 1939, Feynman graduated with a bachelor’s degree and was named a Putnam Fellow.

Feynman’s academic prowess was further demonstrated by his unprecedented perfect score on the physics graduate school entrance exam at Princeton University. He also achieved an outstanding score in mathematics, though his performance in the history and English sections was less remarkable. At Princeton, Feynman’s first seminar, on the classical version of the Wheeler-Feynman absorber theory, was attended by luminaries such as Albert Einstein, Wolfgang Pauli, and John von Neumann. Pauli presciently noted the challenges of quantizing the theory, while Einstein suggested its potential application to gravity in general relativity.

During this period, Feynman’s extraordinary command of theoretical physics was becoming evident. His abilities extended beyond mathematical facility; he possessed an almost intuitive grasp of the physical concepts underlying the equations, a trait shared by few others, such as Einstein and the Soviet physicist Lev Landau.

The Manhattan Project

In 1941, as the United States entered World War II, Feynman’s skills were sought for the war effort. He spent the summer working on ballistics problems at the Frankford Arsenal in Pennsylvania. Later, he was recruited by Robert R. Wilson to contribute to the Manhattan Project, the top-secret effort to develop the atomic bomb.

In early 1943, J. Robert Oppenheimer established the Los Alamos Laboratory in New Mexico, where the atomic bombs were to be designed and built. Feynman joined the Los Alamos team as a junior physicist. His initial role involved administering the computation group, consisting of human computers, within the theoretical division. He collaborated with Stanley Frankel and Nicholas Metropolis to implement IBM punched cards for computation and devised a novel method for calculating logarithms, which he later adapted for use on the Connection Machine. Feynman’s ingenuity extended beyond physics; an avid drummer, he found a way to make the computing machines click in musical rhythms.

Feynman’s work at Los Alamos also included calculating neutron equations for the “Water Boiler,” a small nuclear reactor used to study criticality. He was later sent to the Clinton Engineer Works in Oak Ridge, Tennessee, where the Manhattan Project’s uranium enrichment facilities were located. Upon his return to Los Alamos, Feynman led the group responsible for theoretical work and calculations on the proposed uranium hydride bomb, which ultimately proved infeasible.

At Los Alamos, Feynman engaged in frequent discussions with Niels Bohr. Feynman was one of the few physicists who was not intimidated by Bohr and would challenge his ideas. Feynman said he respected Bohr as much as anyone else, but when discussing physics, he became so focused that he forgot about social niceties. Bohr, however, never seemed to warm up to Feynman.

Feynman’s time at Los Alamos was also marked by his penchant for solving puzzles. He amused himself by cracking the combination locks on the cabinets and desks of his fellow physicists, often discovering that they used easily guessable combinations. His exploits included leaving notes in a colleague’s unlocked filing cabinets, leading the colleague to believe that a spy had infiltrated the laboratory.

During weekends, Feynman would drive to Albuquerque to visit his wife. His frequent trips and safe-cracking activities led Klaus Fuchs, who later confessed to being a Soviet spy, to suggest Feynman as a potential security risk. The FBI compiled a substantial file on Feynman, particularly in light of his security clearance.

Feynman was known for his unconventional behavior. He claimed to have been the only person to witness the first atomic explosion without protective eyewear, reasoning that the windshield of a truck would filter out harmful ultraviolet radiation. The intense brightness of the explosion caused him to duck, and he experienced a temporary afterimage.

Post-War Physics and Quantum Electrodynamics

After his father’s death in 1946, Feynman experienced a period of depression. He sought solace in physics, embarking on projects such as analyzing the physics of a rotating, wobbling disk, inspired by an incident in a Cornell cafeteria. He also studied the work of William Rowan Hamilton on quaternions, attempting, unsuccessfully, to use them to develop a relativistic theory of electrons. Although this work proved important to his later Nobel Prize-winning research, Feynman, feeling burned out, turned his attention to less immediately practical problems. Despite this, he received professorship offers from prestigious institutions like the Institute for Advanced Study, UCLA, and UC Berkeley.

In the post-war years, theoretical physicists faced significant challenges. Quantum electrodynamics (QED), the theory describing the interaction of light and matter, was plagued by infinite integrals in perturbation theory, indicating fundamental mathematical flaws. As Murray Gell-Mann noted, “Theoreticians were in disgrace.”

In June 1947, leading American physicists convened at the Shelter Island Conference. For Feynman, this was his first major conference with prominent figures. The conference addressed the problems in QED, but the experimentalists dominated the discussions with their groundbreaking discoveries, including the Lamb shift, the measurement of the electron’s magnetic moment, and the two-meson hypothesis.

Feynman Diagrams and Renormalization

Feynman developed a novel and widely used pictorial representation for the mathematical expressions governing the behavior of subatomic particles, which became known as Feynman diagrams. These diagrams simplified complex calculations and provided a more intuitive understanding of particle interactions.

Building on the work of Hans Kramers, Hans Bethe derived a renormalized, non-relativistic quantum equation for the Lamb shift. Feynman aimed to create a relativistic version. Using the path integral formulation from his thesis, Feynman obtained a result that matched Bethe’s, but only after introducing a cut-off term to make the integral finite.

Feynman presented his work at the Pocono Conference in 1948. However, his presentation was overshadowed by Julian Schwinger’s extensive exposition of his own approach to QED. Feynman’s unfamiliar Feynman diagrams puzzled the audience, and he struggled to convey his ideas. Prominent physicists like Paul Dirac, Edward Teller, and Niels Bohr raised objections.

Freeman Dyson recognized that Schwinger, Sin-Itiro Tomonaga, and Feynman had independently developed a coherent understanding of QED, though they had not yet published their findings. Dyson became convinced that Feynman’s formulation was the most accessible and ultimately persuaded Oppenheimer of its merits. In 1949, Dyson published a paper that provided rules for implementing renormalization within Feynman’s framework.

Feynman subsequently published his ideas in a series of papers in the Physical Review over three years. His 1948 papers on “A Relativistic Cut-Off for Classical Electrodynamics” attempted to clarify his ideas from the Pocono Conference. His 1949 paper on “The Theory of Positrons” addressed the Schrödinger and Dirac equations and introduced the Feynman propagator. Finally, in papers on the “Mathematical Formulation of the Quantum Theory of Electromagnetic Interaction” (1950) and “An Operator Calculus Having Applications in Quantum Electrodynamics” (1951), he developed the mathematical foundation of his approach.

Initially, papers cited Schwinger’s work more frequently. However, by 1950, papers citing Feynman and utilizing Feynman diagrams became increasingly common. Feynman’s new tool proved to be powerful and accessible, and computer programs were later developed to evaluate Feynman diagrams, enabling high-precision predictions in quantum field theory. Marc Kac adapted Feynman’s path integral technique to the study of parabolic partial differential equations, leading to the Feynman-Kac formula, with applications beyond physics in stochastic processes. Despite the widespread adoption of Feynman diagrams, Schwinger viewed them as a pedagogical aid rather than fundamental physics.

Cornell and Early Career

By 1949, Feynman was becoming restless at Cornell University. He never settled into a permanent residence, living in various temporary accommodations. He also developed a reputation for womanizing. He found Ithaca’s cold winters unpleasant and longed for a warmer climate. Moreover, he felt overshadowed by Hans Bethe at Cornell. Despite these issues, Feynman fondly remembered his time at the Telluride House, a residence for gifted students, where he did much of the work that led to his Nobel Prize.

In 1949, Feynman spent several weeks in Rio de Janeiro. Amid concerns about espionage following the Soviet Union’s first atomic bomb test, Feynman was questioned about his loyalty. Physicist David Bohm’s arrest in 1950 and subsequent emigration to Brazil further fueled these concerns. A girlfriend suggested that Feynman also consider moving to South America. He took a sabbatical in Brazil in 1951-1952, teaching courses at the Centro Brasileiro de Pesquisas Físicas. During his time in Brazil, Feynman became fascinated by samba music and learned to play the frigideira, a metal percussion instrument. He was also an enthusiastic amateur percussionist, playing bongo and conga drums. He spent time in Rio with Bohm, but declined to investigate Bohm’s ideas on physics.

Feynman did not return to Cornell after his sabbatical. Hans Bethe had persuaded him to join the California Institute of Technology (Caltech). As part of the arrangement, Feynman was allowed to spend his first year on sabbatical in Brazil.

Caltech and Later Life

Feynman’s personal life was complex. He met Mary Louise Bell at Cornell, where she studied Mexican art and textiles. She followed him to Caltech, where he gave a lecture. While he was in Brazil, she taught at Michigan State University. They married in 1952 but divorced in 1958.

In the wake of Sputnik in 1957, the U.S. government increased its focus on science. Feynman was considered for a position on the President’s Science Advisory Committee but was not appointed. During this time, the FBI interviewed a woman close to Feynman, possibly his ex-wife Bell, who sent a letter to J. Edgar Hoover expressing her belief that Feynman was either a Communist or strongly pro-Communist and a security risk. Despite these concerns, the U.S. government sent Feynman to the Atoms for Peace Conference in Geneva in 1958.

In Geneva, Feynman met Gweneth Howarth, a British au pair. After a tumultuous period in his love life, Feynman offered her a weekly stipend to become his live-in maid. To circumvent the Mann Act, he arranged for a friend to act as her sponsor. Howarth, who had other boyfriends, accepted Feynman’s offer and moved to California in 1959. She continued to date other men, but Feynman proposed in early 1960. They married in September 1960 and had two children: a son, Carl, and an adopted daughter, Michelle. They maintained homes in Altadena, California, and Baja California.

Feynman experimented with marijuana and ketamine in sensory deprivation tanks, as part of his exploration of consciousness. However, he stopped drinking alcohol when he noticed early signs of alcoholism, as he wanted to avoid any potential damage to his brain. Despite his curiosity about hallucinations, he was hesitant to try LSD.

At Caltech, Feynman continued his groundbreaking research. He investigated the physics of superfluidity in supercooled liquid helium, providing a quantum-mechanical explanation for Lev Landau’s theory. He showed that superfluid helium exhibited macroscopic quantum behavior. This work contributed to the understanding of superconductivity, though the problem was ultimately solved by the BCS theory in 1957.

Feynman’s desire to quantize the Wheeler-Feynman absorber theory led him to develop the path integral formulation and Feynman diagrams.

In collaboration with Murray Gell-Mann, Feynman developed a model of weak decay, demonstrating that the weak interaction involves a combination of vector and axial currents. This work, developed nearly simultaneously by E. C. George Sudarshan and Robert Marshak, was considered seminal because it provided a clear description of the weak interaction and unified Enrico Fermi’s beta decay theory with the concept of parity violation.

Feynman also proposed the parton model to explain the strong interactions governing nucleon scattering. The parton model complemented the quark model developed by Gell-Mann, though the relationship between the two was initially unclear. Feynman’s partons were eventually identified with quarks and gluons, the fundamental constituents of hadrons.

Experiments at the Stanford Linear Accelerator Center (SLAC) in the late 1960s revealed that nucleons contained point-like particles, which were identified as quarks. Feynman’s parton model provided an interpretation of these results.

Feynman did not dispute the quark model. For example, when the fifth quark was discovered in 1977, he predicted the existence of a sixth quark, which was later confirmed.

After his success with quantum electrodynamics, Feynman turned his attention to quantum gravity. Drawing an analogy with the photon (spin 1), he explored the consequences of a massless spin 2 field and derived the Einstein field equations of general relativity. He also developed the concept of “ghosts,” which are particles with an unusual relationship between spin and statistics, and which proved crucial in understanding Yang-Mills theories. Feynman contributed to the understanding of all four fundamental forces of nature: electromagnetism, the weak force, the strong force, and gravity.

Feynman was also interested in the intersection of physics and computation. He was a pioneer in the concept of quantum computing. In the 1980s, he consulted for Thinking Machines Corporation, contributing to the development of early parallel supercomputers and exploring the possibilities of quantum computers. He also developed a variational method for approximating path integrals, which led to significant advancements in calculating critical exponents. Feynman’s famous quote, “What I cannot create, I do not understand,” encapsulated his approach to physics.

Challenger Disaster

Feynman played a crucial role in the Rogers Commission, which investigated the 1986 Challenger disaster. Despite initial reluctance, he was persuaded to participate. He clashed with the commission chairman, William P. Rogers, on several occasions.

Recognition and Awards

Feynman’s contributions to physics were widely recognized. In 1954, he received the Albert Einstein Award. He was also awarded the Ernest Orlando Lawrence Award in 1962. In 1965, he shared the Nobel Prize in Physics with Julian Schwinger and Sin-Itiro Tomonaga “for their fundamental work in quantum electrodynamics.” He was elected a Foreign Member of the Royal Society in 1965, received the Oersted Medal in 1972, and the National Medal of Science in 1979. He was elected to the National Academy of Sciences but later resigned.