Later On

A blog written for those whose interests more or less match mine.

Remembering the Unstoppable Freeman Dyson

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Robbert Dijkgraaf writes in Quanta:

hen Freeman Dyson passed away in February at the age of 96, the world lost one of its most versatile scientists and astute humanists. Trained as a mathematician, Dyson had an appetite for number theory, but his most famous achievement came early as a theoretical physicist, laying out the architecture of modern particle physics. He then moved into the design of nuclear reactors, nuclear-powered space travel, astronomy, astrobiology, climate change and futurism, all while being “a wise observer of the human scene.” He described himself as a frog, not a bird, as he enjoyed jumping from pool to pool, studying their details deeply in the mud. The bird’s-eye perspective was not for him, and he had a lifelong suspicion of grand unified theories.

No life was more entangled with the Institute for Advanced Study, Dyson’s home in Princeton, New Jersey. The English-born scientist came first to the Institute in 1948 as part of an exceptional group of young physicists and mathematicians working with the director, J. Robert Oppenheimer. His colleagues included the future Nobel laureates Hideki Yukawa and Jack Steinberger, as well as Dyson’s first wife, Verena Haefeli, the mother of his eldest children, Esther and George. (In 1958, Freeman married Imme Dyson, a master runner, with whom he had four daughters: Dorothy, Mia, Rebecca and Emily.)

When today’s younger scientists asked Dyson how it felt to be a physicist at the Institute in 1948, in those halcyon days when giants like Albert Einstein and Oppenheimer roamed the grounds, he had great pleasure telling them he wasn’t impressed at all by the famous men. Einstein rarely came to seminars, only when his friend Max von Laue visited, and Oppenheimer did little physics. No, his young colleagues inspired him the most.

It was in his own youth that Dyson had his most celebrated result: the unification of two complementary views of quantum electrodynamics, the theory describing the interaction of light with charged matter. During a postwar visit to the United States, he was fortunate to join the group of young American physicists who had returned from Los Alamos after building the atom bomb. Together, they set their minds on resolving the mysteries of quantum theory. Among them was Richard Feynman, the quirkiest and most brilliant of the bunch. Dyson described him as “half genius and half buffoon.” They made an immediate and lasting connection.

At that time, there were two different approaches toward understanding particle physics. Julian Schwinger at Harvard University had developed a complicated scheme of calculations that was comprehensive, but which few understood. Feynman at Cornell University, on the other hand, had posited a deceptively simple set of diagrams that described the interactions of particles in terms of their trajectories through space and time. In the summer of 1948, while traveling by Greyhound bus from San Francisco to Princeton, Dyson had an epiphany that united the two.

In a flash he understood how Feynman’s straightforward diagrams could perfectly reflect Schwinger’s abstract algebra. A single diagram could in fact be drawn in space and time in many separate ways, interchanging cause and effect, and so each one could capture a whole range of particle behavior. For example, it could describe the emission of a photon by an electron and the subsequent absorption by a second electron, but also the reverse process where the second electron emitted the photon and the first absorbed it. All these processes corresponded exactly with each of the separate calculations in Schwinger’s approach.

It was nothing less than the birth of modern particle physics. Nobel Prizes naturally soon followed — for Schwinger, Feynman and the Japanese physicist Sin-Itiro Tomonaga, who had independently found a third approach. Dyson just missed the boat that by tradition has room for only three passengers, but he often said it was much better when people asked why you didn’t get a Nobel Prize, rather than why you did.

After a brief stay at Cornell, Dyson took up a permanent post at the Institute in 1953, where he stayed until the very end, walking every morning to his office to think and write. A few years into the appointment, he abandoned particle physics. It was time for a jump into a different pool. Dyson threw himself into  . . .

Continue reading.

 

Written by Leisureguy

13 April 2020 at 1:44 pm

Posted in Math, Science

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