Dyson, Freeman (physicist)


(1923- ) British/American Theoretician, Quantum Field Theorist, Mathematical Physicist

Freeman Dyson was a brilliant theorist and mathematician, who discovered the “Rosetta Stone,” capable of harmonizing the relativistic quantum field theoretic language developed by julian seymour schwinger and sin-itiro tomanaga with the space time diagrammatic language of richard phillips feynman into a coherent theory of quantum electrodynamics (QED). In the latter part of his career, he has become famous for his speculative work on the possibility of life on other planets.

Dyson was born on December 15, 1923, in Crowthorne, Berkshire, England, the second child of Sir George Dyson, a gifted composer and conductor, who eventually directed the British Royal College of Music in London, and Mildred Lucy Dyson, a highly educated woman who had been trained as a lawyer. Dyson spoke of his upbringing by parents who began raising their family in their 40s as “more like being with grandparents in their own fashion. It was more intellectual than physical.” Encouraged to explore the arts, Dyson wrote a futuristic novel, “Sir Phillip Roberts’s Erolunar Collision,” inspired by Jules Verne, when he was nine; its tale of a mission to the Moon that is aborted for lack of funding is a blend of science fiction and social satire. He was sent to Twyford, a boarding school, when he was nine and, by age 12, he had won first place in the scholarship exams to Winchester, which had the reputation of being the best mathematical school in England’s public school system. He read popular books about albert einstein and relativity and became increasingly obsessed with mathematics, teaching himself calculus and most of complex function theory from the Encyclopaedia Britannica.

After graduating from Winchester in the summer of 1941, with England already at war, he enrolled at Trinity College, Cambridge University, where England’s greatest mathematicians were then to be found and where paul adrien maurice dirac was the leading light in physics. In 1943, however, his education was interrupted by the British war effort. He was a pacifist in the Gandhi tradition and considered declaring himself a conscientious objector. But the courageous example of the people of his country in their struggle to survive inspired him to do his part. He allowed himself to be recruited into the Royal Air Force Bomber Command at High Wycombe, where he spent his time performing futile statistical studies on the safety and efficacy of the British strategic bombing campaign, which were ignored by the military bureaucracy.

His frustration and sense of impotence at his inability to minimize bomber losses would remain with him for many years.

At the war’s conclusion, Dyson accepted a job as a demonstrator in mathematics at Imperial College, London, but subsequently left mathematics, which he had come to view as an intriguing game, for the “reality” of physics, in which he felt the true challenges lay. When he returned to his studies at Cambridge in 1946, he immersed himself in physics and earned a B.A. Feeling that the United States was the only place to pursue his new field, he decided to do his graduate studies at Cornell University, in order to work with hans albrecht bethe. When he arrived at Cornell in 1947, he quickly became involved in a moment of high drama in the world of physics.

Bethe had just returned from the Shelter Island conference at which willis eugene lamb jr. had announced the observation of a highly significant experimental discrepancy from the predictions of Dirac’s long-accepted theory, which physicists used to calculate the energy levels of the atom. In his experiment Lamb shone a beam of microwaves onto a hot wisp of hydrogen gas blowing from an oven. He found that two fine structure levels in the next lowest group, which should have coincided with the Dirac theory, were in reality shifted relative to each other by a certain amount (the Lamb shift). He measured it with great accuracy and later made similar measurements on heavy hydrogen. On the basis of this experimental discovery Bethe and other quantum theorists such as Schwinger, Feynman, and Tomonaga began to realize that what was missing from Dirac’s theory was a proper interpretation of the unwieldy concept of the self-interaction of the electron, which by its very nature contained infinities, thus preventing a straightforward physical interpretation.

When the electromagnetic field is quantized, according to the rules of quantum mechanics, particles of light called photons are generated. At the heart of the quantum electro-dynamic process is the quantum exchange force through which different electrons interact by exchanging photons with each other; in this context an electron can also exchange a photon with itself. How were physicists to deal with this self-interaction? QED, as it was formulated in the mid-1940s, was not considered to be a rela-tivistically covariant formalism (i.e., it was not formally compatible with the rules of special relativity). This lack of relativistic covariance prevented a unique mathematical interpretation of the physical effects of self-interaction.

Schwinger changed all this when he discovered a relativistically covariant form for QED. This enabled him to introduce the concept of renormalization, which allowed a consistent mathematical interpretation of the self-energy infinities. On the physical level, renormalization implied that physical particles are surrounded by a cloud of “virtual particles,” that is, ghostly particles that exist within the context of the uncertainty principle, whose energy, momentum, and charge modify the physical appearance of the bare original particle. In applying the method of renormalization Schwinger found that the self-energy infinities could be subtracted out. This led to a fully consistent relativistic theory of quantum electrodynamics, which explained the Lamb shift as due to the virtual particle modification of the Coulomb force between the electron and the proton in the hydrogen atom. Using his new relativistically covariant QED formalism with renormalization, Schwinger was also able to calculate the anomalous magnetic moment of the electron.

In the midst of this revolutionary turmoil, Dyson arrived at Cornell as a graduate student with a glowing reputation as a mathematician. Since Bethe had been the first to calculate the Lamb shift theoretically, on the basis of a non-relativistic approximation to electron theory, he gave Dyson the problem of developing a more rigorous version of the Lamb shift in the context of a relativistic electron theory, which ignored the electron’s spin. Dyson found that an exact relativistic calculation could be carried out without impossible complication and gave a finite answer in agreement with Bethe’s earlier approximate Lamb shift calculation.

Freeman Dyson proposed the S-matrix theory of quantum electrodynamics (QED), which unified the relativistic quantum field theory of Julian S. Schwinger and Sin-Itiro Tomanaga with the space-time diagram theory of Richard P. Feynman.

Freeman Dyson proposed the S-matrix theory of quantum electrodynamics (QED), which unified the relativistic quantum field theory of Julian S. Schwinger and Sin-Itiro Tomanaga with the space-time diagram theory of Richard P. Feynman.

While at Cornell, Dyson learned about Schwinger’s new version of QED secondhand, from Victor Weisskopf. He was already forming a friendship with the young Richard Feynman, who had come up with an alternate approach to the problems besetting QED, radically different from Schwinger’s but equally effective. He used space-time diagrams, easily visualized spacetime analogs of the complicated mathematical expressions needed to describe the quantum probabilities of the behavior of electrons, positrons, and photons. His idea of a diagrammatic approach to QED resulted in a highly effective computational scheme. Instead of quantum field operators, his fundamental building blocks were particle processes in space-time. Feynman’s diagrams visualized the construction of the quantum mechanical probabilities associated with fundamental quantum processes in terms of the space-time trajectories of real and virtual particles. More importantly, this space-time diagrammatic formulation of QED had the great advantage of simplifying all of the intricate calculations needed by Schwinger and Tomonaga to predict such interactions in their formulation of QED.

Feynman’s space-time diagrammatic approach to QED intrigued Dyson but seemed magical to him. It troubled him that Feynman was merely writing down answers instead of solving equations in the usual way. Dyson began to conceive his mission as synthesizing these rival theories of QED. In the summer of 1948, Dyson and Feyn-man drove cross-country together, becoming intimate friends. Dyson then spent the summer in Ann Arbor, listening to Schwinger lecture, and came away feeling that Schwinger’s theory was “unbelievably complicated.” At summer’s end, he left Ann Arbor to continue his graduate studies at the Institute of Advanced Study at Princeton, where j. robert oppenheimer was director. On the 48-hour bus ride from Ann Arbor to Princeton, he had an epiphany—the answer to the problem he had been pondering all year. He wrote to his family that his work consisted of a unification of radiation theory, combining the advantageous features of the two theories put forth by Schwinger and Feynman. Now it happened that Schwinger and Feynman talk such completely different languages, that neither of them is able to understand properly what the other is doing. It also happened that I was almost the only young man in the world who had worked with the Schwinger theory from the beginning and had also had long personal contact with Feyn-man at Cornell, so I had a unique opportunity to put the two together.

Without consulting Oppenheimer, he sent off a paper to Physical Review in which he synthesized Feynman’s and Schwinger’s work. This seminal 1949 paper, “The S-Matrix in Quantum Electrodynamics,” formed the basis on which future physicists would devote themselves to problems of renormalization, doing calculations of staggering complexity. Dyson had found the mathematical common ground between Schwinger and Feynman by focusing his attention on the so-called scattering matrix, or S matrix, which described the probability of all of the possible quantum electrodynamic scattering interactions that could occur in spacetime. By using the S-matrix, Dyson derived Feynman’s diagrams from Schwinger’s more complex quantum field operator language. He did this by devising a graphical technique, which enabled him to show that there was a one-to-one correspondence between the S-matrix elements of his graphs and those of the Feynman spacetime diagrams. Thus, the Dyson graphs provided a means of accurately and unambiguously cataloging the arrays of probabilities corresponding to various Feynman spacetime diagrams. Dyson’s formulation was more reliable than Feynman’s and more usable than Schwinger’s. Despite initial opposition by Oppenheimer and others, in January 1949, at the American Physical Society conference in New York city, the Feynman-Dyson method, as it came to be called, was enthusiastically endorsed. Dyson became an overnight celebrity and was offered half a dozen jobs.

In 1949, he returned to England, where he was awarded a prestigious Royal Society Warren Research Fellowship at the University of Birmingham, where he obtained the Ph.D. he had neglected to earn at Cornell. Returning for a year at Princeton, Dyson met and fell in love with Verena Haefeli. Then, after a brief period in Europe, in May 1950, he agreed to succeed Feynman as professor of physics at Cornell. Later that year he and Verena were married. In 1952, finding that he did not like the professorial life, he moved to the Princeton institute as a permanent member. He became a U.S. citizen in 1957, the same year his wife, with whom he had begun a large family, left him. With this cataclysm in his personal life, an era in his scientific life ended, as well. Dyson would never again work on QED or devote himself to the exploration of fundamental physics problems.

In the late 1950s, he took leave from Princeton in order to join the Orion Project research team, which was attempting to build a crewed spacecraft and send it to Mars. Dyson describes his Orion period as one of the happiest times of his life. The project, conceived at the General Dynamics Corporation by former Manhattan Project scientists who were eager to find peaceful uses for nuclear power, aimed to create a propulsion system that would allow human beings to explore the entire solar system. The proposed vehicle, which would have been propelled into space by several repeated nuclear explosions, never made it to the launch pad and was declared defunct in 1965. (The Nuclear Test Ban Treaty of 1963 outlawed it.) Dyson attributed its demise to scientific conservatism.

In the early 1960s, he became a member of the U.S. Arms Control and Disarmament Agency (ACDA) and took part in test ban negotiations. Later in the 1960s, he chaired the Federation of American Scientists, an organization founded in 1945 as the Federation of Atomic Scientists by Oppenheimer and Los Alamos colleagues to address the dangers of the nuclear age.

In addition he has long advocated the exploration and colonization by earthlings of the solar system and beyond and has studied ways of searching for intelligent life. He is well known for his theories about advanced civilizations being able to take a planet like Jupiter apart to build a star-bound biosphere (known in science fiction as a Dyson sphere).

Dyson has said that his real life began at age 45, when he began publishing a series of books interpreting science to the general public. These include Disturbing the Universe, an autobiographical account (1979); Weapons and Hope, reflections on nuclear disarmament (1984); Origins of Life (1985); Infinite in All Directions (1988); and The Sun, the Genome, and the Internet, his exploration of the most important technologies for the 21st century.

Dyson’s great achievement in synthesizing the work of Schwinger and Feynman gave the physics community easy access to the calcula-tional techniques of QED and thus was the key to innumerable future breakthroughs. A complex man and thinker, Dyson has defined his relationship to science differently at different times of his life. Calling himself “an artist with mathematical tools,” he has likened the pleasures of doing mathematical physics with those of writing a novel, “where you as author have complete control over the characters… a self-contained world where you understand everything, the parts and the whole.”

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