Tikalon Blog by Dev Gualtieri

Freeman Dyson (1923-2020)

April 20, 2020

Mathematics is an important part of physics, and those who are extraordinarily proficient in mathematics will become extraordinary physicists. Some ready example include, in no particular order, Isaac Newton, Albert Einstein, Carl Friedrich Gauss, Daniel Bernoulli, William Rowan Hamilton, John von Neumann, Enrico Fermi, Paul Dirac, and Stephen Hawking. Many of these, such as Einstein and Gauss, are known to have excelled in mathematics as young children. Another is Freeman Dyson, who died on February 28, 2020, at age 96.

Photograph of Freeman Dyson (1923-2020) in 2007

Freeman Dyson (1923-2020) in 2007.

Various sources report that as a child he enjoyed reading Eric Temple Bell's, "Men of Mathematics" and was constantly doing calculations on paper as a young child.

He was interested in large numbers and he calculated the number of atoms in the Sun (My estimate, based on a Solar mass of about 2x10³³ grams and the mass of an atom of hydrogen of 1.67x10^-24 grams, is 1.2x10⁵⁷).

Dyson was admitted to Trinity college, Cambridge, UK, on a scholarship at age 15, and at age 17 he studied mathematics with number theorist, G. H. Hardy.

(Wikimedia Commons photograph by Monroem. Click for larger image.)

Dyson entered his professional career just after World War II, which was an exciting time for physics. He came to the United States in 1947 as a Commonwealth Fellow to study at Cornell University (Ithaca, New York) under Hans Bethe for a physics Ph.D., never completed. While at Cornell, he met Richard Feynman (1918-1988), who had joined the Cornell faculty in 1945 after his exit from the Manhattan Project.

Dyson recalled in an interview a four day road trip that he made with Feynman from Cleveland, Ohio, to Albuquerque, New Mexico.[1] As something one would expect from a Feynman road trip, the duo spent a night in a 50-cent room in an Oklahoma brothel as shelter from a heavy rain.[1] Dyson remarked also on Feynman's cavalier approach to mathematical physics.

"So what I was always trying to persuade Feynman was that it's not enough to get the right answers, you have to understand what you're doing. And so we had big arguments about that, and I told him that he ought to learn some quantum field theory if he wanted really to understand this, and he said it just was a language he never would learn and he didn't think it was worth it. As far as he was concerned he thought in pictures and he didn't think in terms of equations. I thought in terms of equations and not in pictures. So we never agreed, but we just had fun talking."[1]

Dyson spent about a year from 1948-1949 at the Institute for Advanced Study, after which he returned to England for a short time as a research fellow at the University of Birmingham. A major problem in physics at that time was how to reconcile electromagnetism and quantum mechanics to create quantum electrodynamics (QED), a complete description of how light and matter matter. Dyson's first-hand experience with Feynman and Julian Schwinger (1918-1994) allowed him to show the equivalence between Feynman's version of QED, based on his eponymous Feynman diagrams, and Schwinger's more traditional operator approach, shared by Japanese physicist, Sin-Itiro Tomonaga (1906-1979), in a 1949 paper.[2]

Dyson refined and popularized Feynman's approach, and Schwinger, Feynman and Tomonaga shared the 1965 Nobel Prize in Physics "for their fundamental work in quantum electrodynamics (QED), with deep-ploughing consequences for the physics of elementary particles."[3] Dyson's reward for his effort was a lifetime appointment at the Institute for Advanced study, arranged by its director, J. Robert Oppenheimer, at the recommendation of Hans Bethe. Oppenheimer had been skeptical of Feynman's approach, but he hired Dyson for proving he was wrong. Dyson became a US citizen in 1957, and he remained a member of the Institute until his death. As for his not getting a share of the Nobel Prize, Dyson said, "I was not inventing new physics... I merely clarified what was already there so that others could see the larger picture."[4]

Feynman diagram of electron-positron annihilation.

The interaction of an electron (e^-) and positron (e⁺) can be elastic, in which case they bounce off each other; or, they can interact and destroy each other in a matter-antimatter annihilation that produces gamma rays (γ).

The nuclear reaction is (e^-) + (e⁺) -> γ + γ.

(Wikimedia Commons image, modified using Inkscape. Click for larger image.)

Quantum electrodynamics has been the most successful theory of physics, since its prediction of the value of the fine structure constant (α) agrees with experiment to 15 parts per billion. For historical reasons, the reciprocal of α is usually given, and the present value of 1/α is 137.035999083.[5] As another example of the way that ideas come to creative people, Dyson's synthesis of QED came to him when he was on a bus crossing Nebraska - "It came bursting into my consciousness, like an explosion... I had no pencil and paper, but everything was so clear I did not need to write it down."[4]

Dyson, who was born on December 15, 1923, in Crowthorne, Berkshire, England, had a mother who was a lawyer and social worker, and a father who was a musician and composer.[4,6] Dyson recalled in his 1979 memoir, "Disturbing the Universe," that one of the happiest times in his life was when he worked through 700 equations in a differential equations textbook in a span from 6 AM to 10 PM when he was on holiday from Winchester college.[4] He wrote that "I was in love with mathematics and nothing else mattered."[4]

Graduating from Cambridge University in 1943, Dyson joined the British war effort as a civilian scientist in the Royal Air Force Bomber Command, where he determined that the Lancaster bomber's gun turrets, rather than helping to protect it, actually made it more vulnerable, since they slowed the plane by about 50 miles per hour and made it less maneuverable.[4] Taking statistics on war deaths convinced Dyson to remain a non-denominational Christian all his life.[4]

In the late 1950s, Dyson was leader of a team that designed a small, low-power nuclear reactor for production of medical isotopes for cancer treatment.[6] He also worked on Project Orion, a spacecraft whose propulsion was by nuclear explosions.[4,6] Such a spacecraft could reach Mars in just two weeks, unlike conventional propulsion that takes a year, or more.[4] Project Orion ended in 1965 because of the Partial Nuclear Test Ban Treaty of 1963, a provision of which prohibited nuclear explosions in space.[4,6]

Dyson's interests extended far beyond the realm of ordinary physics into ideas that seem like science fiction. He proposed a solar system sized megastructure, now called a Dyson sphere, as a means for an advanced civilization to extract as much energy as possible from its star.[4,6] Extraterrestrials would pulverize a planet the size of Jupiter and spread its material into a thin shell around their star. The star, itself would be invisible, but the sphere would emit infrared light.[4] Measurements in 2015 by astronomer, Tabetha S. Boyajian of Louisiana State University, and her colleagues revealed that the light curve from the star, KIC 8462852, was much like what would be expected from a Dyson sphere. As Boyajian stated at the time, there are other reasons for such a light curve.

Dyson also proposed the Dyson tree, a tree genetically modified to grow on comets to produce oxygen for humans. In a gravity-free environment, such trees would grow to heights of hundreds of miles.[4] Dyson trees have been a popular object in science fiction. One book I read, Stephen Baxter's 2001 novel, Manifold: Space, had a Dyson tree that encircled the Earth.

What was surprising to me was Dyson's skepticism about climate change, an opinion he shared with fellow Princetonian and physicist, William Happer. Dyson's viewpoint was that humans are the cause of global warming, but more atmospheric carbon dioxide might be beneficial. Dyson was a member of the Global Warming Policy Foundation, a UK registered charity that opposes government intervention to mitigate climate change.[7]

Dyson, who never completed his Ph.D. had about two dozen honorary degrees, and he was a critic of the Ph.D. system.[6] He said that the system discouraged women and others from science.[6] Dyson dissented from the view that the universe appears to have evolved by blind chance - "The more I examine the universe and the details of its architecture, the more evidence I find that the universe must in some sense have known we were coming."[4] He was a frequent contributor to the New York Review of Books,[4] and his book, "Origins of Life and Weapons and Hope," won the 1984 National Book Critics Circle Award for general nonfiction.[6]

Dyson was against the stockpiling of nuclear weapons, noting that one danger is having such weapons stolen by terrorists to be used against the country from which they were stolen.[7] Likewise, what use are the weapons against individuals, and not countries. He said that "...the problem of nuclear war is basically not technical but human and historical."[7]

As a warning to individuals of Dyson's advanced age and their families, his death was a consequence of a fall he had two days prior during one of his regular visits to his office at the Institute for Advanced Study.[8]

Freeman Dyson (1923-2020)

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