Dyson, Feynman, Von Neumann, and the Dreaded “Warmed-Up Soup”

Paul Halpern
5 min readJul 25, 2021


Renowned physicist Freeman Dyson’s wholly unwarranted fear of being boring

Physicist Freeman Dyson, though he never received an official PhD — a fact he was eminently proud of — was the happy recipient of numerous honorary degrees. From my observations during such a commencement ceremony at my own university, where he was awarded an honorary degree in 2011, one of his great joys at such events was captivating young minds with visions of the future. Despite the sizzling hot weather, unusual for May, his speech was outstanding. He spoke enthusiastically of four impending revolutions: space, nuclear energy, the genome, and computing. Students and other audience members were thrilled!

In 2016, I had the opportunity to thank Dyson at the dedication of the Institute for Advanced Study in Princeton as an American Physical Society Historic Site. Amazingly, we were seated together for dinner, and had the chance to chat. I found him charming and fascinating. His recollections of his friend Richard Feynman, including a story involving Feynman babysitting a pet snake, were particularly noteworthy.

With Freeman Dyson at the Institute for Advanced Study, 2016

On the horizon was a big year for Feynman, as a matter of fact. In 2018, institutions around the world would be celebrating his centenary year. One such event was to be held at the American Physical Society annual meeting in Columbus, Ohio that April.

Richard Feynman

Because of a book I wrote, the session organizer invited me as a speaker. He also asked me to invite Dyson, since we were acquainted with each other. As someone who travelled around the USA with Feynman in the 1940s, who reconciled his version of quantum electrodynamics with Schwinger’s and Tomonaga’s, and who kept in touch with Feynman until the 1980s (Feynman died near the end of that decade), Dyson seemed a natural for the session.

Nervously, I wrote to Dyson in June 2017, and asked him if he’d consider giving a talk about Feynman on his centenary. By then, Dyson was in his early 90s and getting more cautious about travelling. He wrote back that he would think about the question carefully rather than give a quick answer. Mentioning that his advanced age meant that any lecturing commitment must be provisional, he also brought up the fact that he had spoken and written about Feynman so many times. He would only give talk if it was wholly original, not if it was “warmed-up soup,” as he put it.

Recognizing Dyson’s busy schedule and need to slow down because of his age, I was not surprised by his hesitancy to commit. I took the comment about “warmed-up soup,” however, to be simple modesty. Dyson was an incredible speaker. How could he not give an amazing talk about Feynman?

About two months later, on August 6, 2017, I received a note from Dyson in my inbox with disappointing news:

The time has come for a quick decision. Sorry to say, it is no. Memories of Feynman are almost completely faded after 68 years. All that I remember clearly is what I said or wrote in talks and books more recently. In fact, it is warmed-up soup. I heard that phrase spoken loudly by a member of the audience when John von Neumann gave a plenary lecture at the International Conference of Mathematicians in Amsterdam in 1954. Like me, von Neumann had nothing fresh to say, and unlike me, he did not have the wisdom to say no. He was publicly humiliated, and ran out after his talk without waiting for questions. A horrible moment for von Neumann and also for the organizers of the conference.

John von Neumann

John von Neumann was an incredibly brilliant mathematician and logician — one of the founders of modern computer science. His interpretation of quantum mechanics proved highly influential. Dyson, who began his first visiting stay at the Institute for Advanced Study in the late 1940s, and was recruited there later as a permanent member, overlapped with von Neumann’s later years there.

The talk in question that Dyson referenced in his email and had described in far more detail in his published writings was von Neumann’s invited opening address to the International Congress of Mathematicians held in Amsterdam in September 1954. Von Neumann’s lecture was billed as an updated version of an address given by David Hilbert in 1900 to summarize the state of important problems in mathematics. Instead, von Neumann delivered a talk centered on some of the problems he had personally been working on. As he had spoken about such issues at other meetings, it was not a particularly original talk. Dyson happened to be in the audience, and was startled when an audience member called out von Neumann for giving a dullrecap of older endeavors, rather than a visionary look at new ideas. As Dyson recalled, as quoted in his son George Dyson’s book Turing’s Cathedral:

The lecture was about rings of operators, a subject that was new and fashionable in the 1930s. Nothing about unsolved problems. Nothing about the future. Nothing about computers, the subject that we knew was dearest to von Neumann’s heart. Somebody said in a voice loud enough to be heard all over the hall, ‘Aufgewärmte Suppe,’ which is German for ‘warmed-up soup.

Afterward, Dyson recalled, von Neumann walked out of the session with a look of embarrassment. Since then, Dyson has had a fear of giving a talk that is a replica of earlier lectures he gave. Despite being an internationally respected scientist, writer, and speaker, he maintained that insecurity until his final days.

“Quark Soup” Image by Anastasia Ershova: https://sitn.hms.harvard.edu/flash/2020/the-quark-soup/

However, as it turned out, during the Feynman centenary year of 2018, Dyson didn’t say no to everyone. He had accepted an invitation to appear at a major Feynman celebration at Caltech. So perhaps, in the case of turning down the invitation to speak at the American Physical Society event, he was just being polite. Or maybe he felt that he had enough to say for one talk but not for two. At any rate, he delivered an excellent talk at the Caltech event, by all accounts, focusing on Feynman’s contributions to the Challenger shuttle disaster investigation, and to other technical fields such as nanotechnology. It certainly wasn’t “warmed-up soup” he delivered, after all:

In summary, even brilliant physicists who happen to be outstanding speakers harbor insecurities. It is a great lesson for us all.

Paul Halpern is a University of the Sciences physics professor and the author of seventeen popular science books, including Flashes of Creation: George Gamow, Fred Hoyle, and the Great Big Bang Debate.



Paul Halpern

Physicist and science writer. Author of Synchronicity: The Epic Quest to Understand the Quantum Nature of Cause and Effect