Saturday, November 07, 2009

Questions for Dyson

I will be participating in a public Q&A session with Freeman Dyson later this term. Any reader of this blog will know that I'm an admirer of both his work in theoretical physics and his popular writing. (Related posts here.) In preparing for the event, I've been reading and re-reading all sorts of things by and about Dyson. Below is something I found quite striking:

Disturbing the Universe: ... In that spring of 1948 there was another memorable event. Hans [Bethe] received a small package from Japan containing the first two issues of a new physics journal. Progress of Theoretical Physics, published in Kyoto. The two issues were printed in English on brownish paper of poor quality. They contained a total of six short articles. The first article in issue No. 2 was called "On a Relativistically Invariant Formulation of the Quantum Theory of Wave Fields," by S. Tomonaga of Tokyo University. Underneath it was a footnote saying, "Translated from the paper . . . (1943) appeared originally in Japanese." Hans gave me the article to read. It contained, set out simply and lucidly without any mathematical elaboration, the central idea of Julian Schwinger's theory. The implications of this were astonishing. Somehow or other, amid the ruin and turmoil of the war, totally isolated from the rest of the world, Tomonaga had maintained in Japan a school of research in theoretical physics that was in some respects ahead of anything existing anywhere else at that time. He had pushed on alone and laid the foundations of the new quantum electrodynamics, five years before Schwinger and without any help from the Columbia experiments. He had not, in 1943, completed the theory and developed it as a practical tool. To Schwinger rightly belongs the credit for making the theory into a coherent mathematical structure. But Tomonaga had taken the first essential Step. There he was, in the spring of 1948, sitting amid the ashes and rubble of Tokyo and sending us that pathetic little package. It came to us as a voice out of the deep.

A few weeks later, Oppy received a personal letter from Tomonaga describing the more recent work of the Japanese physicists. They had been moving ahead fast in the same direction as Schwinger. Regular communications were soon established. Oppy invited Tomonaga to visit Princeton, and a succession of Tomonaga's students later came to work with us at Princeton and at Cornell. When I met Tomonaga for the first time, a letter to my parents recorded my immediate impression of him "He is more able than either Schwinger or Feynman to talk about ideas other than his own. And he has enough of his own too. He is an exceptionally unselfish person." On his table among the physics journals was a copy of the New Testament.

Ironically, Schweber, in his magisterial book QED and the Men Who Made It, advocates that Dyson deserved a share of the Nobel awarded to Feynman, Schwinger and Tomonaga, and somewhat downplays the role of Tomonaga.

Below are a list of questions I am considering for Dyson (I doubt he'll see it beforehand; does he read my blog? :-). Any suggestions are welcome!

You've written about how depressed you became over your war work analyzing Allied strategic bombing. Yet later you were a Jason, doing top secret military work for the US government. Could you talk about those two experiences, and your opinion about scientists working on weapons and advising the military?

Of the bomb designer turned disarmament activist Ted Taylor, who was the subject of a book called The Curve of Binding Energy, you once said "Very few people have Ted's imagination. ... I think he is perhaps the greatest man that I ever knew well. And he is completely unknown." Could you tell us more about Taylor?

You had a close association with many of the giants of the past -- Feynman, Dirac, Oppenheimer, Bethe. How do you compare them to the best people working today? Would they still be giants?

You advised Francis Crick, while he was still a physicist, that moving into biology might be premature. You thought that biology would eventually be more interesting than physics, but that Crick was too early. What would you be working on today if you were 25 years old?

You wrote that since childhood, some part of you had always known that the “Americans held the future in their hands and that the smart thing for me to do would be to join them.” Do Americans still hold the future in their hands, or will the future be made somewhere else -- for example in Asia or once again in Europe?

You've proposed that genetic engineering might be used for many purposes, from green energy to adapting humans for life in space. What about engineering ourselves for greater intelligence; could that be the next leap forward in human evolution?

You were at Princeton when Everett proposed his "Many Worlds" interpretation of quantum mechanics. Could you describe the reaction to his ideas then (including your own), and your present opinion? Any thoughts on the foundational questions of quantum mechanics?

How well did Feynman understand Second Quantization (or the idea of a quantum field) when he developed his approach to QED? At what point did he really understand the Schwinger / Tomonaga approach?

How much did Dirac understand about the path integral formulation of quantum mechanics before Feynman came along? Feynman was inspired by a formula in one of Dirac's papers, but has claimed that Dirac later acknowledged not knowing whether or how the analogy between amplitude and exponential of action could be made into an equality. Do you have any insight on this?


Sabine Hossenfelder said...

Here's another question: In the review of Brian Greene's book "The Fabric of the Cosmos," Dyson wrote

"According to my hypothesis, the gravitational field described by Einstein's theory of general relativity is a purely classical field without any quantum behavior. Gravitational waves exist and can be detected but they are classical waves and not collections of gravitons. If this hypothesis is true, we have two separate worlds, the classical world of gravitatational and the quantum world of atoms, described by separate theories. The two theories are mathematically different and cannot be applied simultaneously. But no inconsistency can arise from using both theories because any differences between their predictions are physically undetectable."

I would like to know whether he still thinks this regime (in which both theories would have to be applied simultaneously) will remain undetectable. Best,


Steve Hsu said...

Bee, great suggestion!

I actually corresponded with him in 2004 about just this question and whether one can in principle detect a single graviton. If so, one would have to accept that gravity is described by QM, etc.

I proposed some gedanken experiments which could detect single gravitons, but the issue is subtler than I perceived at the time. See

and reference [26] (by our friend Lee) which shows that you can't measure the precise quantum state of the gravitational field unless your detector violates the positive energy condition.

Also see here:

Grim said...

Great questions! Be sure to note the answers well and send them back our way. Thanks!

CW said...

I'm not sure there is a question in this, but see the quote from Dyson in this September 2003 post on Michael Nielsen's blog:

[...] we can see the nature of the flaw which made his life ultimately tragic. His flaw was restlestness, an inborn inability to be idle. Intervals of idleness are probably essential to creative work on the highest level. Shakespeare, we are told, was habitually idle between plays. Oppenheimer was hardly ever idle.

— in the essay "Oppenheimer", reprinted in From Eros to Gaia.

(Nielsen has many references to Dyson's writings—and an interview or two—on his blog.)

Dan said...

I'm with Grim in hoping the talk may be broadcast or that the answers will make their way back across the intertubes.

S.C. Kavassalis said...

This sounds like it should be a very interesting interview - I also would like to see it broadcast in some capacity. I've also wondered about Dirac's feeling on the path-integral formulation- it's interesting if he really didn't see the connection that he, on some level, helped to set up (which, I suppose, is not that uncommon).

I read should get around to reading "Disturbing the universe".

Steve Hsu said...

The plan is to record the discussion, so it will be available online.

Note there's no guarantee all of these questions will make it in.

In Dirac's paper he writes that the quantum amplitude and e^{iS) are "analogous". Later Feynman asked him directly about it (according to Feynman):

F: Did you know they are proportional?

D: Are they?

F: Yes.

D: Oh, that's interesting.

I'd like to know whether F's story is believable to Dyson.

Bruce Charlton said...

It is a bit like your question three - but assuming he does agree that the top modern scientists are duller than they used to be, I wonder whether he would agree with my thesis in

that this is because of the much higher requirement for conscientiousness imposed by a much more prolonged science education/ training process, before independent research is possible (plus a greater emphasis on coursework evaluations and less on examinations).

Dyson himself had a very short, very intense education/ training and did no PhD, as you are probably aware. I believe that the modern science/ academic system would deter or filter-out someone like Dyson long before they got into a position to do independent research.

Steve Hsu said...


In mathematical subjects someone of Dyson's ability can still get to the frontier, make contributions, and become an independent researcher at a fairly young age. For example, see the story of Terence Tao in my more recent post.

Admittedly, almost all subjects in science and mathematics have been explored more deeply than when Dyson was young, so getting to the frontier takes a bit longer. But it is not uncommon for the very best people to be functioning almost independently by their early twenties in mathematical or theoretical subjects.

I don't disagree (overall) with your thesis, but I think it applies much more readily to laboratory or large group science than to theoretical work. Also, I think there is an outlet for very creative and iconoclastic young people that didn't exist in the past: technology startups!

Bruce Charlton said...

Steve - I hope you are correct - indeed I always thought this until a very famous physics prof (not Smolin) told me that nobody at all was trying to do 'revolutionary' science in physics nowadays (presumably he meant nobody in his field).

Assuming for a moment he was correct, the reason could be either that physics is taking some very smart and creative people and forcing them to work on mundane topics, or else the people who get through are smart but not genuinely creative.

Dyson might perhaps have an opinion on whether the above assertion is correct in his experience, and if so an opinion on which of the explanations might apply.

Janus Daniels said...

Dyson's statements on global warming and geo-engineering seem insanely optimistic.

Unknown said...

So, what questions did you ask and is the recording accessible soemwhere?

aseuss said...

"He is more able than either Schwinger or Feynman to talk about ideas other than his own. And he has enough of his own too. He is an exceptionally unselfish person." He's essentially saying that Tomonaga, more so than other scientists Dyson worked with, was open to others and their ideas. He did not merely tout himself; he did not toot his horn. Perhaps that is partly why Caltech scientists were astonished to find that the Japanese were proceeding at a high level in theoretical physics--because the Japanese simply did not tout themselves and published in obscure, Japanese-language journals. Much as they do now. Now, the anecdote about re-discovering this physics is just one instance; I wonder how many times the Japanese discovered or initiated something groundbreaking, especially during this period when scientific communication channels were not robust, but did not receive credit because the findings were published in Japanese language journals and/or Western scientists did not think to look abroad for overlapping research. And of course, there is the popularity contest aspect of any field, and scientists are frankly not immune to that. Dr. Hsu, as a scientist do you think that science is often a popularity contest where those who are good at self-promotion often get the recognition, while equally brilliant and creative researchers often get left in obscurity? It often seems so in this country; I would think that many researchers, even in this country and especially those from abroad--Japan, China, Poland, Hungary--might not get the recognition they deserve. How much of science is politics?

steve hsu said...

Politics and self-promotion play a huge role in science.

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