Farewell Freeman Dyson

He was 96 when he passed last Friday, one of the last giants who participated in the creation of Quantum Electrodynamics and modern quantum field theory.

He has appeared many times on this blog. Below are a few links.

The intestinal fortitude of Freeman Dyson: an account of his visit to the University of Oregon.

The evening began ominously. Dyson had a stomach bug -- he declined to eat anything at dinner, and made several emergency trips to the bathroom. After dinner he fell asleep on a couch in the physics building. Facing a packed auditorium, with people sitting in the aisles and filling an adjoining overflow room with video monitor, the other organizers and I decided that we'd offer Freeman the chance to call the whole thing off when we woke him up. Luckily for everyone, he felt much better after the nap, and was obviously energized by the large and enthusiastic crowd. After we finished the Q&A, he turned to me and said "Well, your questions cured my bug!"

Profile in The Atlantic (2010)

The prodigy in question, Freeman Dyson, now middle-aged, stared ahead, his incessant concentration on the road unbroken. ... I asked him whether as a boy he had speculated much about his gift. Had he asked himself why he had this special power? Why he was so bright?

Dyson is almost infallibly a modest and self-effacing man, but tonight his eyes were blank with fatigue, and his answer was uncharacteristic.

“That’s not how the question phrases itself,” he said. “The question is: why is everyone else so stupid?”

I want to emphasize that Dyson was a lovely and gentle person. The answer above is indeed uncharacterstic. But it is true...

Profile in NYTimes Magazine (2009). Below is a sample of work produced by Dyson between the ages of 5 and 9.

From Disturbing the Universe, one of my favorite scientific memoirs. It describes dramatic events of Dyson's early life: childhood in England, the war, QED, Feynman and Oppenheimer.

... 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.

Rest in Peace, Freeman Dyson.

The Day After Trinity

This was released in 1980 and includes interviews with Rabi, Ulam, Bethe, Frank Oppenheimer, Robert Wilson, and Dyson.

Feynman's cognitive style

Some interesting finds in this 1966 AIP oral history interview with Feynman.

I have always felt that Feynman was cognitively a bit "lopsided" -- much stronger mathematically than verbally. This might be partially responsible for his way of learning -- it was often easier for him to invent his own solution than to read through someone else's lengthy paper. (Personality factors such as his independent streak, and his strong creativity, also play a role.) But this sometimes left him with gaping holes in knowledge. In contrast, Schwinger had at age 17 an encyclopedic understanding of what was known about quantum electrodynamics -- he had read and mastered all of the literature as a high school kid!

This excerpt reveals that Feynman did not understand the conventional formulation of QED even after Dyson's paper proving the equivalence of the Feynman and Schwinger methods. (When someone explained the action of a creation operator on the vacuum, Feynman reportedly objected "How can you create an electon? It disagrees with conservation of charge!" :-)

... I was struggling gradually to learn. I mean, I had to learn something to prove the connection between my thing and the same thing. Dyson had done a great deal in that direction. That didn’t satisfy me because I couldn’t follow that. Dyson told me, when he wrote his paper, “Don’t bother to read it, there’s nothing in it that you don’t know, except that it proves it’s the same as what everybody else knows, but it doesn’t say anything different or do anything different than is in your paper. Nothing more in it,” he told me.

... Yeah, because I remember him telling me not to worry about the paper. It hadn’t anything in it, you see. ... But then I thought I had to understand the connection, for publication purposes and others. And I had a good opportunity, because Case sent me his theorem — the manuscript of a big paper that he was going to publish in the Physical Review, which had all the steps of the theorem. Now, I argued in the meantime with myself, in my usual physical way of arguing, and concluded for several physical reasons, by some examples and other things — simpler examples that weren’t so elaborate as the calculations I made — that it couldn’t be true that the two methods would give the same result. ... I prepared a letter in which I wrote the physical arguments. Then I decided, that isn’t going to convince him. Nobody pays any attention to physical arguments, no matter how good they are. I’ve got to find a mistake in the proof. But the proof has creation and annihilation operators and all kinds of stuff. So I went to some students, in particular Mr. Scalator who was only fair, but he understood. He had learned in a pedestrian way what it all meant, and he explained to me what the symbols meant. So I learned like a little child what all this was about, so I understood what the symbols that he was using in the paper meant, and I tried to follow the proof, and I learned enough to be able to do that kind of mathematics, see — for the first time. So I followed the whole thing through, and I found a mistake, a very simple algebraic error, in the proof. He commuted some things that didn’t commute and so on.

Feynman never carefully read either Schwinger or Tomonaga's work:

Weiner: How about Tomonaga’s work? When did you first hear of it?
Feynman: I don’t know when I first heard of it. The work itself, I never knew exactly what it was, and I don’t yet know precisely what it was.
Weiner: You read his paper?
Feynman: No.
Weiner: I mean, there’s one paper that is often cited —
Feynman: No. No. I don’t think I read the paper. But this must be understood — I don’t mean anything disparaging. If Schwinger hadn’t been in the front yard at Pocono, or next to me, I wouldn’t have known what he did either. I got the same as everybody else. If you can do it yourself, why learn how somebody else does it? So I don’t know precisely what the relation of Tomonaga’s and Schwinger’s work is or the relation of his and mine. I think the relation of Tomonaga’s work to my work is very small. I mean, I think he’s gone around much closer the direction that Schwinger went.
Weiner: I think it’s the general impression.
Feynman: But I don’t know the precise relationship of their work. But I believe, if I’m not mistaken, although you’ll have to ask Schwinger, that everything that Schwinger did he did without knowledge of what Tomonaga did. I hear, but I don’t know, that Tomonaga did a very great deal, and did essentially what Schwinger did, except perhaps for working on certain practical problems. I don’t know. That’s what I hear. But I don’t know. I’m sorry, that sounds stupid, but I have never looked into it, and I never read Schwinger’s paper in a comprehensible way. I don’t know what’s in that paper of Schwinger’s.
Weiner: Haven’t tried to read it?
Feynman: Never. Tried in the sense that I looked at it and I flipped the pages, because it’s too hard. I read it at a time when I didn’t even know what a creation-annihilation operator was. I read it — you probably can prove that by the fact that I refer to it in various places, and get certain formulas out of it — I read it in the same way that I talk to him. When something looks like something, I know that’s it, you know? But I didn’t follow all the steps. I never followed all the steps.
Weiner: But you did know, when you talked to him at Pocono, and then —
Feynman: I know Schwinger — that’s what I say, I must have read it in pieces and bits. I know what Schwinger did; I know more or less how he did it. ...

Feynman: Yes, because we talked together, we had the physical idea of what starts it, but there’s a difference from that and checking all the equations, ... I don’t know whether he really read mine in detail or not. But he knows what’s in it, and I know what’s in his, but I can’t tell you. Perhaps if I look at his paper carefully, I can see that I really did read it, you know? I mean, I’d have to have it and look at it and see if I did read it. That’s a good way to look. I doubt that I read it in detail. I doubt that I looked at all of the various complicated sub-things that he had to worry about, like what to do with the longitudinal waves — because I don’t think there’s any problem with the longitudinal waves. I couldn’t pay attention to such a thing, see? So I doubt that I’ve ever read the paper in any careful way like a student would try to learn it. I don’t believe I’ve ever done that.

Finally, an interesting conversation between Feynman and Oppenheimer concerning the covariant propagator and positrons as electrons moving backwards in time:

So I went to the Physics Society and gave this paper, and I wanted Professor Oppenheimer to hear it, and other people like that. I particularly wanted Oppenheimer to hear it because he often said that there wasn’t anything to it. He understood Schwinger’s and he didn’t understand mine. And I thought he would be at the meeting. I’d kind of half thought about him when I prepared it. When I went to the meeting, he wasn’t there, but I gave the paper, and then Weisskopf got up and said, “This paper is so important and unusual” and so on “that we ought to give the man more time to express his ideas.” ... Then I stepped down, and just at that moment, Oppenheimer came in and sat down in the chair just ahead of me. And he turned around and said, “What did you talk about?” I said, “The idea of electrons going backwards,” meaning positrons. He said, “Oh, I heard all that. Oh, yes,” he said, “I heard that stuff, right? That stuff I heard.” I said, “Yeah, you’ve heard it, but you’ve never understood it.” Now, the response to that was an invitation I found in the mail when I got back to Cornell, to come to Princeton to the Institute and explain all my ideas, in as many lectures as I wished, two a week, as long a time as I wanted, expenses to be paid by the Institute, and so on. He’s a very great man, I know. I mean, I understand him. We’re good friends. You know. I mean, it’s not enemies. I said that because I was trying to get something across to him, that he didn’t understand it. That was honest. He knew that if I were driven to say that that was true — you know what I mean — and it was worth learning. So I said that, and his response was very generous — any length of time I want, any conditions. So I went to the Institute of Advanced Study.

In his eulogy, Schwinger described Feynman as "... the outstanding intuitionist of our age ..." :-)

Note added: I recalled another anecdote related to this post. At his Pocono talk Feynman was repeatedly asked by Dirac "Is it unitary?" (referring to Feynman's diagram method deduced from the path integral). Unfortunately, Feynman did not seem sure what "unitary" meant and responded "perhaps it will become clear as we proceed..." (a trick he learned from an earlier Schwinger talk). Feynman also did not seem to know what an S-matrix was!

But is it unitary?  :-)

See follow up post: Feynman and the secret of magic.

Sitzfleisch

Freeman Dyson reviews the new biography of Oppenheimer by Ray Monk. I discussed the book already here.

NYBooks: ... The subtitle, “A Life Inside the Center,” calls attention to a rarer skill in which Oppenheimer excelled. He had a unique ability to put himself at the places and times at which important things were happening. Four times in his life, he was at the center of important events. In 1926 he was at Göttingen, where his teacher Max Born was one of the leaders of the quantum revolution that transformed our view of the subatomic world. In 1929 he was at Berkeley, where his friend Ernest Lawrence was building the first cyclotron, and with Lawrence he created in Berkeley an American school of sub-atomic physics that took the leadership away from Europe. In 1943 he was at Los Alamos building the first nuclear weapons. In 1947 he was in Washington as chairman of the General Advisory Committee of the United States Atomic Energy Commission, giving advice to political and military leaders at the highest levels of government. He was driven by an irresistible ambition to play a leading part in historic events. In each case, when he was present at the center of action, he rose to the occasion and took charge of the situation with unexpected competence.

... In 1939 Oppenheimer published with his student Hartland Snyder a paper, “On Continued Gravitational Contraction,” only four pages long, which is in my opinion Oppenheimer’s one and only revolutionary contribution to science. In that paper, Oppenheimer and Snyder invented the concept of black holes; they proved that every star significantly more massive than the sun must end its life as a black hole, and deduced that black holes must exist as real objects in the sky around us. They showed that Einstein’s theory of general relativity compels any massive star that has exhausted its supply of nuclear fuel to enter a state of permanent free fall. Permanent free fall was a new idea, counterintuitive and profoundly important. It allows a massive star to keep falling permanently into a black hole without ever reaching the bottom.

Einstein never imagined and never accepted this consequence of his theory. Oppenheimer imagined it and accepted it. As a direct result of Oppenheimer’s work, we now know that black holes have played and are playing a decisive part in the evolution of the universe. That is the historical fact. The mystery is Oppenheimer’s failure to grasp the importance of his own discovery. He lived for twenty-seven years after the discovery, never spoke about it, and never came back to work on it. Several times, I asked him why he did not come back to it. He never answered my question, but always changed the conversation to some other subject.

It is true, as Monk demonstrates, that Oppenheimer’s ruling passion was to be a leader in pure science. He considered his excursions into bomb-making and nuclear politics to be temporary interruptions. My interactions with Oppenheimer confirm Monk’s picture of him. I worked at the Institute for Advanced Study for almost twenty years while Oppenheimer was director. He rarely talked about politics and almost never about bombs, but talked incessantly about the latest discoveries and puzzles in pure science.

... Oppenheimer continued for the rest of his life to be proud of his achievement at Los Alamos. ... Monk expresses his opinion, with which I agree, that Oppenheimer’s anger arose from his deep loyalty to America. For him, expressing regret for what he had done for his country would have meant joining his country’s enemies.

... Oppenheimer was above all a good soldier. That is why he worked so well with General Groves, and that is why Groves trusted him. I have a vivid memory of the ice-cold February day in 1967 when we held a memorial service for Oppenheimer at Princeton. Because of the extreme cold, attendance at the service was sparse. But General Groves, old and frail, came all the way from his home to pay his respects to his friend. ...

The real tragedy of Oppenheimer’s life was not the loss of his security clearance but his failure to be a great scientist. For forty years he put his heart and soul into thinking about deep scientific problems. With the single exception of the collapse of massive stars at the end of their lives, he did not solve any of these problems. Why did he not succeed in scientific research as brilliantly as he succeeded in soldiering and administration? I believe the main reason why he failed was a lack of Sitzfleisch. Sitzfleisch is a German word with no equivalent in English. The literal translation is “Sitflesh.” It means the ability to sit still and work quietly. He could never sit still long enough to do a difficult calculation. His calculations were always done hastily and often full of mistakes. In a letter to my parents quoted by Monk, I described Oppenheimer as I saw him in seminars:

He is moving around nervously all the time, never stops smoking, and I believe that his impatience is largely beyond his control.

In addition to his restlessness, Oppenheimer had another quality, emphasized by Monk in the subtitle of his book. He always wanted to be at the center. This quality is good for soldiers and politicians but bad for original thinkers. ...

I have to admit that my own Sitzfleisch, while well above average for a normal person, is probably less than required for true excellence in theoretical physics. (This might have something to do with my being less aspie than the typical theorist ;-)

Dyson on philosophy and the gravitational free lunch

Freeman Dyson in The NY Review of Books:

When and why did philosophy lose its bite? How did it become a toothless relic of past glories? These are the ugly questions that Jim Holt’s book compels us to ask. Philosophers became insignificant when philosophy became a separate academic discipline, distinct from science and history and literature and religion. The great philosophers of the past covered all these disciplines. Until the nineteenth century, science was called natural philosophy and officially recognized as a branch of philosophy. The word “scientist” was invented by William Whewell, a nineteenth-century Cambridge philosopher who became master of Trinity College and put his name on the building where Wittgenstein and I were living in 1946. Whewell introduced the word in the year 1833. He was waging a deliberate campaign to establish science as a professional discipline distinct from philosophy.

Whewell’s campaign succeeded. As a result, science grew to a dominant position in public life, and philosophy shrank. ...

He also tells the story of Gamow and Einstein crossing the street:

Quantum uncertainty allows the temporary creation of bubbles of energy, or pairs of particles (such as electron-positron pairs) out of nothing, provided that they disappear in a short time. The less energy is involved, the longer the bubble can exist. Curiously, the energy in a gravitational field is negative, while the energy locked up in matter is positive. If the Universe is exactly flat, then as Tryon pointed out the two numbers cancel out, and the overall energy of the Universe is precisely zero. In that case, the quantum rules allow it to last forever. If you find this mind-blowing, you are in good company. George Gamow told in his book My World Line (Viking, New York, reprinted 1970) how he was having a conversation with Albert Einstein while walking through Princeton in the 1940s. Gamow casually mentioned that one of his colleagues had pointed out to him that according to Einstein's equations a star could be created out of nothing at all, because its negative gravitational energy precisely cancels out its positive mass energy. "Einstein stopped in his tracks," says Gamow, "and, since we were crossing a street, several cars had to stop to avoid running us down".

Gamow's statement (at least as it appears above) is not quite correct. There are zero energy compact objects in general relativity, but they are quite special and not like ordinary stars. See here and also this blog post (2007):

... years ago I wrote a paper (unpublished) showing how to obtain a zero energy configuration in GR out of massive constituents. Particle theorists I discussed it with all thought I was crazy, but the referee was a very erudite relativist, who pointed out that a similar result (using different constructions) had been obtained by ADM, Novikov and Zeldovich, and others long ago.

Cosmic Dyson

My neighbor in Eugene recommended this Atlantic article on Freeman Dyson, and now I'm recommending it to you :-)

... “It is said that the mental processes of a mathematical prodigy differ in no essential respect from those of ordinary folks who can handle more modest problems,” George Dyson had written—not Freeman’s tree-dwelling son, but Sir George Dyson, Freeman’s father, a composer and the director of the Royal College of Music. “The prodigy’s gift is the power of incessant concentration on more and more complicated mental calculations, until his brain can instantly recall the end products of the thousands of factors with which his mind has been busy.”

The prodigy in question, Freeman Dyson, now middle-aged, stared ahead, his incessant concentration on the road unbroken. He seemed mesmerized by the oncoming pavement, or by some idea or formulation glimpsed in the immateriality beyond the pavement. I asked him whether as a boy he had speculated much about his gift. Had he asked himself why he had this special power? Why he was so bright?

Dyson is almost infallibly a modest and self-effacing man, but tonight his eyes were blank with fatigue, and his answer was uncharacteristic.

“That’s not how the question phrases itself,” he said. “The question is: why is everyone else so stupid?”


... His second book, Darwin Among the Machines, is a history of the luminaries of the information revolution, and as such signals a turn back toward the world of his father. His third, Project Orion, is a history of his father’s spacecraft. His next, Turing’s Cathedral, he conceives as “a creation myth for the digital universe.”

This July in Dick’s Tavern, George [Dyson -- the author, and Freeman's son] was hard at work finishing Turing’s Cathedral, trying to meet an August deadline for delivery of the manuscript. Mounted on the tavern wall, running the length of the bar, was the skeletal frame for one of his Aleut-style kayaks, 25 feet long, with three manholes for paddlers. Beneath this unfinished vessel, the pages of Turing’s Cathedral were laid out in neat stacks along the bar surface, about two chapters per bar stool. The inspiration for the book seems to have come in 1961, when George was 8 and he and a small band of comrades—the sons of field theorists at the Institute for Advanced Study—stumbled upon an old barn on the institute’s campus. Stored inside, along with old farm equipment, were the relics of the antediluvian electronic computer on which John von Neumann conducted his pioneering experiments in artificial intelligence. In Darwin Among the Machines, in a chapter called “Rats in a Cathedral,” George describes how he and his buddies, with wrenches and screwdrivers, lobotomized von Neumann’s machinery. “We blindly dissected the fossilized traces of electromechanical logic out of which the age of digital computers first took form.”

... FREEMAN DYSON is a national and international treasure. His career demonstrates how a Nobel-caliber mind, in avoiding the typical laureate’s dogged obsession with a single problem, can fertilize many fields, in his case particle physics and astrophysics, biology and exobiology, mathematics, metaphysics, the history of science, religion, disarmament theory, literature, and even medicine, as Dyson was a co-inventor of the TRIGA reactor, which produces medical isotopes.

Dyson, clearly a busy man, was extraordinarily generous with his time with me at an early stage of my career. His allowing me to be present at an intimate family affair—his reunion with George—provided the climax and denouement for my best and most successful book. In the field, Dyson was an amusing and never-boring companion. Never have I had a relationship of such asymmetrical understanding. Dyson always got the drift of my ideas and sentences before I was three or four words into them, but the converse was not true. When the physicist spoke of his own pet subjects—quantum electrodynamics, say, or certain characteristics of the event horizon in the vicinity of black holes—I had no idea what he was talking about. Dyson is a discoverer of, and fluent in, the mathematics by which the fundamental laws of the universe operate, and in that language I am illiterate.

Long ago I asked Ted Taylor, the chief of Project Orion, what quality distinguished Dyson from the other Orion men. “Freeman’s gift?” said Taylor. “It’s cosmic. He is able to see more interconnections between more things than almost anybody. He sees the interrelationships, whether it’s in some microscopic physical process or in a big complicated machine like Orion. He has been, from the time he was in his teens, capable of understanding essentially anything that he’s interested in. He’s the most intelligent person I know.”

This is how Dyson strikes me too. But the operative word for me is cosmic. The word terrestrial would not apply. In taking the measure of the universe, Dyson fails only in his appraisal of the small, spherical piece of the cosmos under his feet. Or so it seems to me. For whatever reason, he is emotionally incapable of seeing the true colors of the rampant ingenuity of our species and calculating where our cleverness, as opposed to our wisdom, is taking us.

Kenneth Brower, a longtime contributor to The Atlantic, is the author of 13 books, including The Starship and the Canoe (1978), a dual portrait of Freeman and George Dyson.

Dyson, the bomb, and the Japanese surrender

This interview with Freeman Dyson pointed me to the recent reanalysis by historian Tsuyoshi Hasegawa of the Japanese surrender at the end of WWII. There is an old controversy over whether the atomic bombs or the entry of the USSR played the decisive role. Were the bombs necessary at all? Dyson mentions (about 30 minutes into the interview) that, due to Hasegawa, he is now 90 percent confident that they were not. This despite his close association with many of the Manhattan Project figures (Oppenheimer, Bethe, Teller, Feynman and others), and his acceptance for sixty years that atomic weapons played the key role. Dyson's recapitulation in the interview is quite good (it starts at about 20 minutes); see also here.

I recently learned from Donald Keene's diary translations (see also here) that Japanese modernizers had been worried about the Russian threat since the Meiji era.

Dyson also has some interesting comments about space exploration and genomics immediately following the discussion about nuclear weapons. I almost skipped listening to this interview, having spent several hours with him relatively recently. But someone as knowledgeable and brilliant as Dyson will always generate surprising insights.


Hasegawa's book: Racing the Enemy: Stalin, Truman, and the Surrender of Japan

Summary: ... According to Hasegawa, Japanese leaders' diaries and testimonies suggest that the imminent Soviet invasion was more influential in compelling them to accept the Potsdam conditions. Although Emperor Hirohito's desire to end the war became more urgent after Hiroshima, only on August 9 after the Soviet declaration of war did he clearly say that "it is necessary to study and decide on the termination of the war" [26]. The other peace advocates in the Foreign Ministry on the same day began to urge acceptance of the Potsdam ultimatum [27]. The reactions of the more hawkish military officials seem to have been similar. Both Admiral Toyoda and Army Deputy Chief of Staff Kawabe were surprised at the news of Hiroshima but were not ready to temper their views on continuing the war [28]. Many military officials hoped to mount a final defense, but had counted on Soviet neutrality in order to do so [29]. The Soviet declaration of war destroyed those hopes, and severely weakened the war faction's leverage within the government.

The major strength of Hasegawa's work, and one reason for its new arguments, is its in-depth analysis of Japanese primary sources. Few previous historians in the US had consulted the personal writings of figures like Toyoda, Kawabe, and Tanemura. But Hasegawa also makes more extensive use of Allied primary sources, including the memoirs and diaries of Truman, Byrnes, Brown, and others, which play a key role in his argument about the intent of the Potsdam Proclamation. Hasegawa's careful scholarship has significantly enriched our understanding of the intentions behind the demand for "unconditional surrender," as well as the dynamics behind the Japanese decision to surrender.

I recently had a memorable conversation with a colleague (another former Junior Fellow) who is a professor in the history department. Despite early evidence of talent in mathematics, he decided to study history because he wanted a career in which his abilities would continue to grow and deepen well into maturity. He preferred to reach the peak of his powers late in life, rather than suffer the continuous decline so dreaded by precocious young geniuses in theoretical subjects. I begin to see his point.

Dyson video

The video from our December 2009 public discussion with Freeman Dyson is available here. (I think this should automatically stream if you have QuickTime, but otherwise you might end up downloading a 170MB .mov file.)

See here for earlier discussion and a link to a transcript.

The intestinal fortitude of Freeman Dyson

The evening began ominously. Dyson had a stomach bug -- he declined to eat anything at dinner, and made several emergency trips to the bathroom. After dinner he fell asleep on a couch in the physics building. Facing a packed auditorium, with people sitting in the aisles and filling an adjoining overflow room with video monitor, the other organizers and I decided that we'd offer Freeman the chance to call the whole thing off when we woke him up. Luckily for everyone, he felt much better after the nap, and was obviously energized by the large and enthusiastic crowd. After we finished the Q&A, he turned to me and said "Well, your questions cured my bug!"

The questions we asked are listed below. You'll have to wait to watch the video in order to hear the answers!

[Video. Transcript.]

CAMBRIDGE

You write that scientists come in two varieties: hedgehogs and foxes. Foxes know many tricks, hedgehogs only one. Which kind of scientist makes the most important discoveries?

Of course, molecular biology was being born at that moment. But you advised Francis Crick, while he was still a physicist, that moving into biology might be premature. He didn’t take your advice did he, and a few years later he helped discern the structure of DNA? Mistake on your part?


MOVE TO AMERICA

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.” Was that why you made your home in America? Do Americans still hold the future in their hands.

In the 50s, many people were fascinated with the potential of nuclear energy. Admiral Lewis L. Strauss, then Chairman of the U.S. Atomic Energy Commission, when he said: "It is not too much to expect that our children will enjoy electrical energy in their homes too cheap to meter." Did you share this excitement?

There were plans to build a nuclear airplane that would fly for a year at a time and you got involved with a nuclear rocket project-- the Orion Project. Tell us about that.

Weren’t you involved in the project’s demise—the test ban treaty?


THE SCIENTIFIC PROCESS

Now about the nature of science. You write, “Science is an art form and not a philosophical method. The great advances in science usually result from new tool rather than from new doctrines.” Could you elaborate?

Physics leads to some pretty weird places. 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?

It’s been said that Quantum Electrodynamics or QED is the most successful theory science has ever produced, having been verified in some cases to an accuracy of 12 decimal places. It was worked out by two geniuses, Feynman and Schwinger, but their theories looked totally at odds—one used diagrams the other formal analysis. In perhaps your most celebrated piece of physics, you showed they were equivalent. I’m curious, did Feynman and Schwinger grasp immediately what you had done?

You write, “Heretics who question the dogmas are needed... I am proud to be a heretic. The world always needs heretics to challenge the prevailing orthodoxies.” Do we need more heretics today?


WILD IDEAS

From science fact to science fiction. Your speculations about the future of humanity include the Dyson tree and the Dyson sphere. A Dyson tree is a genetically engineered plant capable of growing on a comet. You think comets are promising places for life..how so?

You've proposed that genetic engineering might be used for many purposes, from green energy to adapting humans for life in space…even to people growing their own dogs. Please tell us more.

What about engineering ourselves for greater intelligence; could that be the next leap forward in human evolution?


SCIENCE AND CULTURE

Jacques Hadamard said “It is important for him who wants to discover not to confine himself to one chapter of science, but to keep in touch with various others. ” Have scientists and mathematicians seized or squandered opportunities to learn from others in different disciplines?

To what extent should the public's view influence the path of science?

As a great observer of science, you’ve seen how science can evoke excessive hype and fear….has the negative public reaction to things like nuclear energy, GMOs, nanotechnology…has this surprised you?


SCIENCE AND RELIGION

Science and religion. There are scientists, like NIH chief Francis Collins, who believe in God and think religion is compatible with science. There are scientists, who are what you call passionate atheists—Hardy, Erdos, Dawkins, who think religion is a massive irrational distraction. You say that religion must be explored from the inside and those atheists, even very smart philosophers like Dan Dennett, will never understand it. How so?


In 2000, you were awarded the Templeton Prize for Progress in Religion. You wrote, "I am neither a saint nor a theologian. To me, good works are more important than theology." What did you mean?


WRAP UP

We’ve spoken about science and religion, let’s end talking about technology. You write, “Technology is a gift of God. After the gift of life, it is perhaps the greatest of God's gifts. It is the mother of civilizations, of arts and of sciences.” In your lifetime, those gifts include biotechnology, computers, and the Internet. What gifts might lie in our future?

What would you be working on today if you were 25 years old?

I will report the answers to some of my dinner questions. About Dirac and the path integral, Dyson thought that Feynman's story was probably true -- Dirac did not know that the quantum amplitude and the exponential of the action were more than "analogous" (indeed, they are proportional) until after Feynman had worked it out. It was also Feynman who had the idea of the sum over classical paths. In Dirac's paper the exponential of the action might have been a quantum operator, like the time evolution operator, which is the exponential of the Hamiltonian.

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 also asked about the infamous night with Feynman in the hotel in Oklahoma, and Dyson confirmed the accuracy of Feynman's recollection :-)

An evening with Freeman Dyson

This is turning into a bit of a production -- 4 HD cameras and professional editing will hopefully result in a nice documentary video. Click for larger version of poster.

See Questions for Dyson.

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?

Freeman Dyson

The Times magazine has a long profile of Freeman Dyson this week. The article focuses mainly on his heretical stance on global warming, but there are some good tidbits about his childhood and main scientific contributions. For the latter, I suggest the book QED and the men who made it by S. Schweber. Dyson started as a mathematician, and obtained interesting results in number theory while a student and during the war. In a reference letter provided for his application to graduate school in physics he was characterized as the best mathematician in England at the time, though only 23 years of age.

Below is a sample of work produced by Dyson between the ages of 5 and 9.



The following is from a 2005 Dyson email; we later had an extended correspondence about whether the gravitational field need be quantized and whether black holes were the most efficient graviton detectors.

...Thank you very much for sending me your four papers. I read three of them and will soon read the fourth. All interesting. But to me the most interesting is the discrete Hilbert Space paper, especially your reference [2] proving that lengths cannot be measured with error smaller than the Planck length. I was unaware of this reference but I had reached the same conclusion independently.

From the Times profile:

NYTimes: ...During World War II, Dyson worked for the Royal Air Force at Bomber Command, calculating the most effective ways to deploy pilots, some of whom he knew would die. Dyson says he was “sickened” and “depressed” that many more planes were going down than needed to because military leadership relied on misguided institutional mythologies rather than statistical studies. Even more upsetting, Dyson writes in “Weapons and Hope,” he became an expert on “how to murder most economically another hundred thousand people.” This work, Dyson told the writer Kenneth Brower, created an “emptiness of the soul.”

Then came two blinding flashes of light. Dyson’s reaction to Hiroshima and Nagasaki was complicated. Like many physicists, Dyson has always loved explosions, and, of course, uncovering the secrets of nature is the first motivation of science. When he was interviewed for the 1980 documentary “The Day After Trinity,” Dyson addressed the seduction: “I felt it myself, the glitter of nuclear weapons. It is irresistible if you come to them as a scientist. To feel it’s there in your hands. To release the energy that fuels the stars. To let it do your bidding. And to perform these miracles, to lift a million tons of rock into the sky, it is something that gives people an illusion of illimitable power, and it is in some ways responsible for all our troubles, I would say, this what you might call ‘technical arrogance’ that overcomes people when they see what they can do with their minds.”

Eventually, Dyson would be sure nuclear weapons were the worst evil. But in 1945, drawn to these irreducible components of life, Dyson left mathematics and took up physics. Still, he did not want to be another dusty Englishman toiling alone in a dim Cambridge laboratory. Since childhood, some part of him 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.” That the United States was now the country of Einstein and Oppenheimer was reason enough to go, but Dyson’s sister Alice says that “he escaped to America so he could make his own life,” removed from the shadow of his now famous musical father. “I know how he felt,” says Oliver Sacks, who came to New York not long after medical school. “I was the fifth Dr. Sacks in my family. I felt it was time to get out and find a place of my own.”

In 1947, Dyson enrolled as a doctoral candidate at Cornell, studying with Hans Bethe, who had the reputation of being the greatest problem-solver in physics. Alice Dyson says that once in Ithaca, her brother “became so much more human,” and Dyson does not disagree. “I really felt it was quite amazing how accepted I was,” he says. “In 1963, I’d only been a U.S. citizen for about five years, and I was testifying to the Senate, representing the Federation of American Scientists in favor of the nuclear-test-ban treaty.”

After sizing him up over a few meals, Bethe gave Dyson a problem and told him to come back in six months. “You just sit down and do it,” Dyson told me. “It’s probably the hardest work you’ll do in your life. Without having done that, you’ve never understood what science is all about.” This smaller problem was part of a much larger one inherited from Einstein, among others, involving the need for a theory to describe the behavior of atoms and electrons emitting and absorbing light. Put another way, it was the question of how to move physics forward, creating agreement among the disparate laws of atomic structure, radiation, solid-state physics, plasma physics, maser and laser technology, optical and microwave spectroscopy, electronics and chemistry. Many were working on achieving this broad rapport, including Julian Schwinger at Harvard University; a Japanese physicist named Shinichiro Tomonaga, whose calculations arrived in America from war-depleted Kyoto on cheap brown paper; and Feynman, also at Cornell, a man so brilliant he did complex calculations in his head. Initially, Bethe asked Dyson to make some difficult measurements [calculations?] involving electrons. But soon enough Dyson went further.

The breakthrough came on summer trips Dyson made in 1948, traveling around America by Greyhound bus and also, for four days, in a car with Feynman. Feynman was driving to Albuquerque, and Dyson joined him just for the pleasure of riding alongside “a unique person who had such an amazing combination of gifts.” The irrepressible Feynman and the “quiet and dignified English fellow,” as Feynman described Dyson, picked up gypsy hitchhikers; took shelter from an Oklahoma flood in the only available hotel they could find, a brothel, where Feynman pretended to sleep and heard Dyson relieve himself in their room sink rather than risk the common bathroom in the hall; spoke of Feynman’s realization that he had enjoyed military work on the Manhattan Project too much and therefore could do it no more; and talked about Feynman’s ideas in a way that made Dyson forever understand what the nature of true genius is. Dyson wanted to unify one big theory; Feynman was out to unify all of physics. Inspired by this and by a mesmerizing sermon on nonviolence that Dyson happened to hear a traveling divinity student deliver in Berkeley, Dyson sat aboard his final Greyhound of the summer, heading East. He had no pencil or paper. He was thinking very hard. On a bumpy stretch of highway, long after dark, somewhere out in the middle of Nebraska, Dyson says, “Suddenly the physics problem became clear.” What Feynman, Schwinger and Tomonaga were doing was stylistically different, but it was all “fundamentally the same.”

Dyson is always effacing when discussing his work — he has variously called himself a tinkerer, a clean-up man and a bridge builder who merely supplied the cantilevers linking other men’s ideas. Bethe thought more highly of him. “He is the best I have ever had or observed,” Bethe wrote in a letter to Oppenheimer, who invited Dyson to the institute for an initial fellowship. There, with Einstein indifferent to him and the chain-smoking Oppenheimer openly doubting Dyson’s physics, Dyson wrote his renowned paper “The Radiation Theories of Tomonaga, Schwinger and Feynman.” Oppenheimer sent Dyson a note: “Nolo contendere — R.O.” If you could do that in a year, who needed a Ph.D.? The institute was perfect for him. He could work all morning and, as he wrote to his parents, in the afternoons go for walks in the woods to see “strange new birds, insects and plants.” It was, Dyson says, the happiest sustained moment in his life. It was also the last great discovery he would make in physics.

Some heresies from Freeman Dyson

See here, and this 2005 U Michigan commencement address.

Will Dyson get Watsonized, or are these heresies insufficiently dangerous?

..all the fuss about global warming is grossly exaggerated. Here I am opposing the holy brotherhood of climate model experts and the crowd of deluded citizens who believe the numbers predicted by the computer models. ... I have studied the climate models and I know what they can do. ... They do a very poor job of describing the clouds, the dust, the chemistry and the biology of fields and farms and forests. They do not begin to describe the real world that we live in.

and

...I say the United States has less than a century left of its turn as top nation. Since the modern nation-state was invented, about the year 1500, a succession of countries have taken turns as top nation. First it was Spain, then France, then and Britain, than America. Each term lasted about 150 years. Ours began in 1920 so it should end about 2070.

The reason why each top nation's term comes to an end is that the top nation becomes overextended militarily, economically and politically. Greater and greater efforts are required to maintain the number one position. Finally, the overextension becomes so extreme that the whole structure collapses. Already we can see in the American posture today some clear symptoms of overextension.

Who will be the next top nation? It might be the European Union or it might be China. After that it might be India or Brazil. You should be asking yourself not how to live in an America-dominated world, but how to prepare for a world that is not America dominated. That may be the most important problem for your generation to solve. How does a people who think of themselves as number one yield gracefully to become number two? So I'm telling you misfortunes are on the way.

Dyson and Crick

From this essay.

Also, Dyson is sceptical about global warming, but knows enough to be sceptical of his scepticism.

Bad Advice to a Young Scientist

Sixty years ago, when I was a young and arrogant physicist, I tried to predict the future of physics and biology. My prediction was an extreme example of wrongness, perhaps a world record in the category of wrong predictions. I was giving advice about future employment to Francis Crick, the great biologist who died in 2005 after a long and brilliant career. He discovered, with Jim Watson, the double helix. They discovered the double helix structure of DNA in 1953, and thereby gave birth to the new science of molecular genetics. Eight years before that, in 1945, before World War 2 came to an end, I met Francis Crick for the first time. He was in Fanum House, a dismal office building in London where the Royal Navy kept a staff of scientists. Crick had been working for the Royal Navy for a long time and was depressed and discouraged. He said he had missed his chance of ever amounting to anything as a scientist. Before World War 2, he had started a promising career as a physicist. But then the war hit him at the worst time, putting a stop to his work in physics and keeping him away from science for six years. The six best years of his life, squandered on naval intelligence, lost and gone forever. Crick was good at naval intelligence, and did important work for the navy. But military intelligence bears the same relation to intelligence as military music bears to music. After six years doing this kind of intelligence, it was far too late for Crick to start all over again as a student and relearn all the stuff he had forgotten. No wonder he was depressed. I came away from Fanum House thinking, “How sad. Such a bright chap. If it hadn’t been for the war, he would probably have been quite a good scientist”.

A year later, I met Crick again. The war was over and he was much more cheerful. He said he was thinking of giving up physics and making a completely fresh start as a biologist. He said the most exciting science for the next twenty years would be in biology and not in physics. I was then twenty-two years old and very sure of myself. I said, “No, you’re wrong. In the long run biology will be more exciting, but not yet. The next twenty years will still belong to physics. If you switch to biology now, you will be too old to do the exciting stuff when biology finally takes off”. Fortunately, he didn’t listen to me. He went to Cambridge and began thinking about DNA. It took him only seven years to prove me wrong. The moral of this story is clear. Even a smart twenty-two-year-old is not a reliable guide to the future of science. And the twenty-two-year-old has become even less reliable now that he is eighty-two.

Freeman Dyson on biotech

Read this Freeman Dyson essay (NY Review of Books) on the future of biotechnology.

This is true, but it makes me a little sad, despite the hope it represents for our future:

It has become part of the accepted wisdom to say that the twentieth century was the century of physics and the twenty-first century will be the century of biology. Two facts about the coming century are agreed on by almost everyone. Biology is now bigger than physics, as measured by the size of budgets, by the size of the workforce, or by the output of major discoveries; and biology is likely to remain the biggest part of science through the twenty-first century. Biology is also more important than physics, as measured by its economic consequences, by its ethical implications, or by its effects on human welfare.

The following is also true, and it makes me smile :-)

I see a close analogy between John von Neumann's blinkered vision of computers as large centralized facilities and the public perception of genetic engineering today as an activity of large pharmaceutical and agribusiness corporations such as Monsanto. The public distrusts Monsanto because Monsanto likes to put genes for poisonous pesticides into food crops, just as we distrusted von Neumann because he liked to use his computer for designing hydrogen bombs secretly at midnight. It is likely that genetic engineering will remain unpopular and controversial so long as it remains a centralized activity in the hands of large corporations.

I see a bright future for the biotechnology industry when it follows the path of the computer industry, the path that von Neumann failed to foresee, becoming small and domesticated rather than big and centralized. The first step in this direction was already taken recently when genetically modified tropical fish with new and brilliant colors appeared in pet stores. For biotechnology to become domesticated, the next step is to become user-friendly. I recently spent a happy day at the Philadelphia Flower Show, the biggest indoor flower show in the world, where flower breeders from all over the world show off the results of their efforts. I have also visited the Reptile Show in San Diego, an equally impressive show displaying the world of another set of breeders. Philadelphia excels in orchids and roses, San Diego excels in lizards and snakes. The main problem for a grandparent visiting the reptile show with a grandchild is to get the grandchild out of the building without actually buying a snake.

Every orchid or rose or lizard or snake is the work of a dedicated and skilled breeder. There are thousands of people, amateurs and professionals, who devote their lives to this business. Now imagine what will happen when the tools of genetic engineering become accessible to these people. There will be do-it-yourself kits for gardeners who will use genetic engineering to breed new varieties of roses and orchids. Also kits for lovers of pigeons and parrots and lizards and snakes to breed new varieties of pets. Breeders of dogs and cats will have their kits too.

What about the kits for humans?

The following might be a bit exaggerated:

Now, after three billion years, the Darwinian interlude is over. It was an interlude between two periods of horizontal gene transfer. The epoch of Darwinian evolution based on competition between species ended about ten thousand years ago, when a single species, Homo sapiens, began to dominate and reorganize the biosphere. Since that time, cultural evolution has replaced biological evolution as the main driving force of change. Cultural evolution is not Darwinian. Cultures spread by horizontal transfer of ideas more than by genetic inheritance. Cultural evolution is running a thousand times faster than Darwinian evolution, taking us into a new era of cultural interdependence which we call globalization. And now, as Homo sapiens domesticates the new biotechnology, we are reviving the ancient pre-Darwinian practice of horizontal gene transfer, moving genes easily from microbes to plants and animals, blurring the boundaries between species. We are moving rapidly into the post-Darwinian era, when species other than our own will no longer exist, and the rules of Open Source sharing will be extended from the exchange of software to the exchange of genes. Then the evolution of life will once again be communal, as it was in the good old days before separate species and intellectual property were invented.

This I've heard before:

The reductionist physics and the reductionist molecular biology of the twentieth century will continue to be important in the twenty-first century, but they will not be dominant. The big problems, the evolution of the universe as a whole, the origin of life, the nature of human consciousness, and the evolution of the earth's climate, cannot be understood by reducing them to elementary particles and molecules. New ways of thinking and new ways of organizing large databases will be needed.

The rest of the essay paints a utopian future of green technology. Dyson even thinks green technology will solve the problem of rural poverty, which he links to "grey" (industrial) technology that has concentrated wealth in the cities of the north. I hope Dyson is right, but he neglects the extent to which innovation is driven by small numbers of smart people, often working in networks. I doubt innovation will be as evenly distributed as he thinks.

Kamikazes and terrorists

Freeman Dyson reflects on kamikaze pilots and Islamic terrorists in the New York Review of Books. (See the very end of the article, which is mostly a review of Daniel Dennett's book on religion and natural science.) I have heard it said many times that men die in battle for friends in their unit, rather than for flag and country.

The best source of information about modern Islamic terrorists that I know of is a book, Understanding Terror Networks, by Marc Sageman.[1] Sageman is a former United States foreign service officer who worked with the Mujahideen in Afghanistan and Pakistan. In chapter 5 of his book, he describes in detail the network that planned and carried out the September 2001 attacks on the United States. He finds that the bonds holding the group together, during its formative years in Hamburg, were more personal than political. He concludes: "Despite the popular accounts of the 9/11 perpetrators in the press, in-group love rather than out-group hate seems a better explanation for their behavior."

To end this review, I would like to introduc another recently published book, Kamikaze Diaries: Reflections of Japanese Student Soldiers, by Emiko Ohnuki-Tierney.[2] This contains extensive extracts from diaries written by seven of the young men who died in suicidal missions or as kamikaze pilots in the closing months of World War II. The diaries give us firsthand testimony of the thoughts and feelings of these young soldiers who knew that they were fated to die. Their thoughts and feelings are astonishingly lucid and free from illusions. Some of them expressed their feelings in poetry. All of them were highly educated and familiar with Western literature in several languages, having spent most of their brief lives in reading and writing. Only one of them, Hayashi Ichizo, was religious, having grown up in a Japanese Christian family. His Christian faith did not make self-sacrifice easier for him than for the others. He had read Kierkegaard's Sickness unto Deathand carried it with him on his final mission together with his Bible.

All of the young men, including Hayashi, had a profoundly tragic view of life, mitigated only by happy memories of childhood with family and friends. They were as far as it was possible to be from the brainwashed zombies that contemporary Americans imagined to be piloting the kamikaze planes. They were thoughtful and sensitive young men, neither religious nor nationalistic fanatics.

Here I have space to mention only one of them, Nakao Takanori, who must speak for the rest. Nakao left a poem beginning, "How lonely is the sound of the clock in the darkness of the night." In his last letter to his parents, a week before his death, he wrote,

At the farewell party, people gave me encouragement. I did my best to encourage myself. My co-pilot is Uno Shigeru, a handsome boy, aged nineteen, a naval petty officer second class. His home is in Hyogo Prefecture. He thinks of me as his elder brother, and I think of him as my younger brother. Working as one heart, we will plunge into an enemy vessel. Although I did not do much in my life, I am content that I fulfilled my wish to live a pure life, leaving nothing ugly behind me.

We have no firsthand testimony from the young men who carried out the September 11 attacks. They were not as highly educated and as thoughtful as the kamikaze pilots, and they were more influenced by religion. But there is strong evidence that they were not brainwashed zombies. They were soldiers enlisted in a secret brotherhood that gave meaning and purpose to their lives, working together in a brilliantly executed operation against the strongest power in the world. According to Sageman, they were motivated like the kamikaze pilots, more by loyalty to their comrades than by hatred of the enemy. Once the operation had been conceived and ordered, it would have been unthinkable and shameful not to carry it out.

Hedgehogs, Foxes and Feynman

Freeman Dyson reviews the recently published collection of Feynman's letters, collected by his daughter Michelle. The essay is long, but worth reading in full. I feel Dyson underrates Feynman a bit, and his classification of thinkers as hedgehogs (Einstein) or foxes (Feynman) is too black and white. Our scientific activities are shaped by the questions of our day. Einstein had the opportunity to solve foundational puzzles (the problems and data were at hand) -- did Feynman? (Also true of Dirac, who Dyson rates as a "greater genius" than Feynman.) Certainly, Feynman had broad interests, but it is also clear that he kept returning to deeper issues like turbulence (strangely not classified as a deep issue at the time), interpretation of quantum mechanics (EPR, probability, etc.) and quantum gravity. I might add that 100 years from now his early interest in quantum computing could be remembered as particularly significant. Although he didn't develop any key algorithms (or even, if I recall correctly, explore the notion of universal quantum computers built from simple gates), he was the first to note the exponential power of quantum computers and the qualitative difference between quantum and classical computing.

Why should we care about Feynman? What was so special about him? Why did he become a public icon, standing with Albert Einstein and Stephen Hawking as the Holy Trinity of twentieth-century physics? The public has demonstrated remarkably good taste in choosing its icons. All three of them are genuinely great scientists, with flashes of true genius as well as solid accomplishments to their credit. But to become an icon, it is not enough to be a great scientist. There are many other scientists, not so great as Einstein but greater than Hawking and Feynman, who did not become icons. Paul Dirac is a good example of a scientist greater than Feynman. Feynman always said, whenever the opportunity arose, that the "space-time approach" that led him to his new way of doing particle physics was directly borrowed from a paper of Dirac's.[6] That was true. Dirac had the original idea and Feynman made it into a useful practical tool. Dirac was the greater genius. But Dirac did not become an icon because he had no wish to be an icon and no talent for entertaining the public. Scientists who become icons must not only be geniuses but also performers, playing to the crowd and enjoying public acclaim. Einstein and Feynman both grumbled about the newspaper and radio reporters who invaded their privacy, but both gave the reporters what the public wanted, sharp and witty remarks that would make good headlines. Hawking in his unique way also enjoys the public adulation that his triumph over physical obstacles has earned for him. I will never forget the joyful morning in Tokyo when Hawking went on a tour of the streets in his wheelchair and the Japanese crowds streamed after him, stretching out their hands to touch his chair. Einstein, Hawking, and Feynman shared an ability to break through the barriers that separated them from ordinary people. The public responded to them because they were regular guys, jokers as well as geniuses. The third quality that is needed for a scientist to become a public icon is wisdom. Besides being a famous joker and a famous genius, Feynman was also a wise human being whose answers to serious questions made sense. To me and to hundreds of other students who came to him for advice, he spoke truth. Like Einstein and Hawking, he had come through times of great suffering, nursing Arline through her illness and watching her die, and emerged stronger. Behind his enormous zest and enjoyment of life was an awareness of tragedy, a knowledge that our time on earth is short and precarious. The public made him into an icon because he was not only a great scientist and a great clown but also a great human being and a guide in time of trouble. Other Feynman books have portrayed him as a scientific wizard and as a storyteller. This collection of letters shows us for the first time the son caring for his father and mother, the father caring for his wife and children, the teacher caring for his students, the writer replying to people throughout the world who wrote to him about their problems and received his full and undivided attention.