Showing posts sorted by relevance for query bethe. Sort by date Show all posts
Showing posts sorted by relevance for query bethe. Sort by date Show all posts

Saturday, March 28, 2009

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.

Sunday, January 18, 2009

The Age of Computing

A remarkable essay by Nick Metropolis, which appeared in Daedalus (winter 1992). Originally trained as an experimental physicist, Metropolis played an important role in the Manhattan project and was a pioneer in electronic computation. The Metropolis Algorithm, used in Monte Carlo simulation, bears his name.
The Age of Computing: A Personal Memoir

In the history of modern technology, computer science must figure as an extraordinary chapter, and not only because of the remarkable speed of its development. It is unfortunate, however, that the word "science" has been widely used to designate enterprises that more properly belong to the domain of engineering.

"Computer science" is a glaring misnomer, as are "information science," "communication science," and other questionable "sciences." The awe and respect which science enjoys and which engineering is denied is inexplicable, at least to one who sees the situation from the other side. ...

Since World War II, the discoveries that have changed the world were not made so much in lofty halls of theoretical physics as in the less-noticed labs of engineering and experimental physics.

The roles of pure and applied science have been reversed; they are no longer what they were in the golden age of physics, in the age of Einstein, Schrodinger, Fermi and Dirac. Readers of Scientific American, nourished on the Wellsian image of science, will recoil from even entertaining the idea that the age of physical "principles" may be over.

The laws of Newtonian mechanics, quantum mechanics and quantum electrodynamics were the last in a long and noble line that appears to have somewhat dried up in the last 50 years. As experimental devices (especially measuring devices) are becoming infinitely more precise and reliable, the wealth and sheer mass of new and baffling raw data collected by experiment greatly exceeds the power of human reason to explain them.

Physical theory has failed in recent decades to provide a theoretical underpinning for a world which increasingly appears as the work of some seemingly mischievous demiurge. The failure of reason to explain fact is also apparent in the life sciences, where "theories" (of the kind that physics has led us to expect) do not exist; many are doubtful that this kind of scientific explanation will ever be successful in explaining the secrets of life.

...Historians of science have always had a soft spot for the history of theoretical physics. The great theoretical advances of this century -- relativity and quantum mechanics -- have been documented in fascinating historical accounts that have captivated the mind of the cultivated public.

There are no comparable studies of the relations between science and engineering. Breaking with the tradition of the Fachidiot, theoretical physicists have bestowed their romantic autobiographies on the world, portraying themselves as the high priests of the reigning cult.


By their less than wholly objective accounts of the development of physics, historians have conspired to propagate the myth of science as being essentially theoretical physics. Though the myth no longer described scientific reality 50 years ago, historians pretended that all was well, that nothing had changed since the old heroic days of Einstein and his generation.

There were a few dissenters, however, such as the late Stanislaw Ulam, who used to make himself obnoxious by proclaiming that Enrico Fermi was "the last physicist." He and others who proclaimed such a possibility were prudently ignored.

Physicists did what they could to keep the myth alive. With impeccable chutzpah, they went on promulgating new "laws of nature" and carefully imitated their masters of another age. With dismaying inevitability, many of these latter-day "laws" have been exposed as quasi-mathematical embellishments, devoid of great physical or scientific significance.

Historians of science have seen fit to ignore the history of the great discoveries in applied physics, engineering and computer science, where real scientific progress is nowadays to be found. Computer science in particular has changed and continues to change the face of the world more thoroughly and more drastically than did any of the great discoveries in theoretical physics.

... Although the basic rules for the computation of reliability were long known, it took several years during and immediately after World War II for the importance of the concept of reliability to be explicitly recognized and dealt with. Only then did reliability computation become an essential feature in computer design.

The late Richard Feynman was one of the first to realize the centrality of reliability considerations in all applied scientific work. In the early days of the Manhattan Project in Los Alamos (in 1943 and early 1944), he tested the reliability of his first program in a dramatic fashion, setting up a day-long contest between human operators working with hand-operated calculators and the first electromechanical IBM machines.

At first, human operators showed an advantage over the electromechanical computers; as time wore on, however, the women who worked with the calculators became visibly tired and began to make small errors. Feynman's program on the electromechanical machine kept working. The electromechanical computers won out by virtue of their reliability.

Feynman soon came to realize that reliable machines in perfect working order were far more useful than much of what passed for theoretical work in physics, and he loudly stated that conviction. His supervisor, Hans Bethe -- the head of T-Division (T for theory) at the time and a physicist steeped in theory -- at first paid no attention to him.

At the beginning of the Manhattan project, only about a dozen or so hand-operated machines were available in Los Alamos; they regularly broke down, thereby slowing scientific work. In order to convince Bethe of the importance of reliable computation, Feynman recruited me to help him improve the performance of the hand-operated desk calculators, avoiding the week-long delays in shipping them to San Diego for repairs. We spent hours fixing the small wheels until they were in perfect order. Bethe, visibly concerned when he learned that we had taken time off from our physics research to do these repairs, finally saw that having the desk calculators in good working order was as essential to the Manhattan Project as the fundamental physics.

Throughout his career, Feynman kept returning to the problem of the synthesis of reliable computers. Toward the end of his life, he gave a remarkable address at the 40th anniversary of the Los Alamos Laboratory where he sketched a reliability theory based on thermodynamical analogies.

In contrast to Bethe, John von Neumann very quickly realized the importance of reliability in the design of computers. It is no exaggeration to say that von Neumann had some familiarity (in the 1950s) with all the major ideas that have since proved crucial in the development of supercomputers.

...The first large-scale electronic computer to be built, the one that may be said to inaugurate the computer age, was the ENIAC. It was built at the Moore School of the University of Pennsylvania by an engineer and a physicist -- Presper Eckert and John Mauchly. Their idea, trivial by the standards of our day, was a revolutionary development when completed in 1945.

At the time, all electromechanical calculators were built exclusively to perform ordinary arithmetic operations. Any computational scheme involving several operations in a series or in parallel had to be planned separately by the user. Mauchly realized that if a computer could count, then it could do finite-difference schemes for the approximate solution of differential equations. It occurred to him that such schemes might be implemented directly on an electronic computer, an unheard of idea at the time.

...Of all the oddly named computers, the MANIAC's name turned out to be the most unfortunate: George Gamow was instrumental in rendering this and other computer names ridiculous when he dubbed the MANIAC "Metropolis And von Neumann Install Awful Computer."

Fermi and Teller were the first hackers. Teller would spend his weekends at the laboratory playing with the machine. Fermi insisted on doing all the menial work himself, down to the least details, to the awed amazement of the professional programmers. He instinctively knew the right physical problems that the MANIAC could successfully handle.

His greatest success was the discovery of the strange behavior of nonlinear systems arising from coupled nonlinear oscillators. The MANIAC was a large enough machine to allow the programming of potentials with cubic and even quartic terms. Together with John Pasta and Stanislaw Ulam, he programmed the evolution of a mechanical system consisting of a large number of such coupled oscillators. His idea was to investigate the time required for the system to reach a steady state of equidistribution of energy. By accident one day, they let the program run long after the steady state had been reached. When they realized their oversight and came back to the computer room, they noticed that the system, after remaining in the steady state for a while, had then departed from it, and reverted to the initial distribution of energy (to within 2 percent).

The results were published in what was to be the last paper Fermi published before he died. Fermi believed this computer-simulated discovery to be his greatest contribution to science. It is certainly the first major scientific discovery made by computer, and it is not fully understood to this day (though it has spawned some beautiful ideas). ...

[Metropolis was not up to date on ergodic theory, integrability and chaos?]

Tuesday, June 23, 2015

Schwinger meets Rabi


Seventeen year old Julian Schwinger meets Columbia professor I. I. Rabi (Nobel Prize 1944) and explains the EPR paper to him.
Climbing the Mountain: The Scientific Biography of Julian Schwinger [p.22-23] ... Rabi appeared; he invited Motz into his office to discuss 'a certain paper by Einstein in the Physical Review! Motz introduced Julian and asked if he could bring his young friend along; Rabi did not object, and so it began.

The Einstein article turned out to be the famous paper of Einstein, Podolsky, and Rosen, with which young Julian was already familiar. He had studied quantum mechanics with Professor Wills at the City College, and discussed with him the problem of the reduction of a wave packet after additional information about a quantum system is gained from a measurement. 'Then they [Rabi and Motz] began talking and I sat down in the corner. They talked about the details of Einstein's paper, and somehow the conversation hinged on some mathematical point which had to do with whether something was bigger or smaller, and they couldn't make any progress. Then I spoke up and said, "Oh, but that is easy. All you have to do is to use the completeness theorem." Rabi turned and stared at me. Then it followed from there. Motz had to explain that I knew these things. I recall only Rabi's mouth gaping, and he said, "Oh, I see. Well, come over and tell us about it." I told them about how the completeness theorem would settle the matter. From that moment I became Rabi's protege. He asked, "Where are you studying?" "Oh, at City College." "Do you like it there?" I said, "No, I'm very bored."''

Watching young Julian demonstrate such 'deep understanding of things that were at the time at the frontier and not clearly understood,' Rabi decided on the spot to talk to George Pegram, then chairman of the physics department and dean of the graduate faculty, to arrange Julian's immediate transfer to Columbia. He and Motz left Julian waiting and went to see Pegram ...
Hans Bethe (Nobel Prize 1967) supported the transfer :-)
[p.24] Bethe provided an enthusiastic letter of support after he read Julian's notes on electrodynamics.'' Bethe's letter, dated 10 July 1935, reads as follows:
Dear Rabi,

Thank you very much for giving me the opportunity to talk to Mr. Schwinger. When discussing his problem with him, I entirely forgot that he was a sophomore 17 years of age. I spoke to him just as to any of the leading theoretical physicists. His knowledge of quantum electrodynamics is certainly equal to my own, and I can hardly understand how he could acquire that knowledge in less than two years and almost all by himself.

He is not the frequent type of man who just "knows" without being able to make his knowledge useful. On the contrary, his main interest consists in doing research, and in doing it exactly at the point where it is most needed at present. That is shown by his choice of his problem: When studying quantum electrodynamics, he found that an important point had been left out in a paper of mine concerning the radiation emitted by fast electrons. That radiation is at present one of the most crucial points of quantum theory. ...
Climbing the Mountain is one of the best scientific biographies I have read, on par with books by Pais on Einstein and Oppenheimer, and by Schweber on QED. The account of the early communication between Schwinger and Feynman about their very different formulations of QED is interesting. See also Feynman's cognitive style and Feynman and the secret of magic.

Schwinger was one of the 64 mid-career scientists studied by Harvard psychologist Anne Roe.

Schwinger, of course, did not believe in wavefunction collapse or other Copenhagen mysticism: see Schwinger on Quantum Foundations.

Tuesday, November 20, 2012

Schwinger on quantum foundations



The excerpt below is from the excellent biography Climbing the Mountain by Mehra and Milton. Milton was one of Schwinger's last Harvard grad students, eventually a professor at the University of Oklahoma. Schwinger's view is the one shared by all reasonable physicists: quantum mechanics must apply to the measuring device as well as that which is measured. Once this assumption is made (as Hawking and others have noted): many worlds follows trivially.
(p.369) Schwinger: "To me, the formalism of quantum mechanics is not just mathematics; rather it is a symbolic account of the realities of atomic measurements. That being so, no independent quantum theory of measurement is required -- it is part and parcel of the formalism.

[ ... recapitulates usual von Neumann formulation: unitary evolution of wavefunction under "normal" circumstances; non-unitary collapse due to measurement ... discusses paper hypothesizing stochastic (dynamical) wavefunction collapse ... ]

In my opinion, this is a desperate attempt to solve a non-existent problem, one that flows from a false premise, namely the vN dichotomization of quantum mechanics. Surely physicists can agree that a microscopic measurement is a physical process, to be described as would any physical process, that is distinguished only by the effective irreversibility produced by amplification to the macroscopic level. ..."
Similar views have been expressed by Feynman and Gell-Mann and by Steve Weinberg. Interestingly, this chapter in the biography seems to describe (in slightly odd language) some Schwinger work on decoherence, analyzing a collaborator's claim that Stern-Gerlach beams could be recombined coherently.

See also my paper On the origin of probability in quantum mechanics.

Schwinger's precocity, explored in the biography in far greater detail than I had seen before, is overwhelming. At age 17 or so he had read everything there was to read about quantum mechanics, early field theory, nuclear and atomic physics. For example, he had read and understood Dirac's papers, had invented the interaction picture basis, had already read the Einstein, Podolsky, Rosen paper and explained it to Rabi when they first met. He met Bethe and they discussed a problem in quantum scattering (Schwinger had improved Bethe's well-known result and noticed an error that no other theorist had). Bethe later wrote that the 17 year old Schwinger's grasp of quantum electrodynamics was at least as good as his own.
Feyerabend on the giants: "... The younger generation of physicists, the Feynmans, the Schwingers, etc., may be very bright; they may be more intelligent than their predecessors, than Bohr, Einstein, Schrodinger, Boltzmann, Mach and so on. ..."
Schwinger survived both Feynman and Tomonaga, with whom he shared the Nobel prize for quantum electrodynamics. He began his eulogy for Feynman: "I am the last of the triumvirate ..."

Friday, August 17, 2012

"For the historians and the ladies"

The excerpts below are from interviews with Benoit Mandelbrot.

On the birth of molecular biology under Max Delbruck at Caltech:
I would say the more important event was quite outside of my life's work, the arrival of Max Delbruck. Now Max Delbruck was, I think, one of the great personalities of those times. He was a physicist by training, a man belonging to one of the very highest families in Prussia, in many ways a great liberal, in many ways a great authoritarian. 
Max Delbruck had been told in the '30s, according to rumour, that he was just not good enough to be doing physics as well as he hoped; that while Bethe would spend a few hours and write seventeen pages of flawless mathematics, and Weisskopf wrote only fifteen, but equally flawless - and Pauli always preferred Bethe to Weisskopf because of this difference - well, Delbruck only wrote five and there were bugs to fix. He was not up to this competition, which he was finding himself in. 
But he had branched into biology, the first physicist (to do so). Schrödinger had written about him in his book What Is Life? Delbruck had suddenly become a challenge. And the challenge was met by an equally remarkable man named Beadle who was a farmer from Nebraska who had gone to university to learn more about corn to improve the yield of his farm and moved on, and by that time had become the chairman of the Biology division at Caltech. Beadle was a very bold person. He hired Delbruck, who knew no biology, and told him, "You go and learn biology by teaching Biology One to freshmen, and then go on and do your thing," - which was to introduce quantum mechanics ideas into biology. 
Now, I never knew what they were doing. They were very - I wouldn't say secretive, they were just a little elusive. They never said what they were doing. Well it was clear they were doing something extraordinarily exciting which for me was again this very strong hope of bringing hard mathematical or physical thinking to a field, which had been very soft before.
"For the historians and the ladies"; saved by Oppenheimer and von Neumann:
... I met Oppenheimer now and then, and then saw him in a train from Princeton to New York. We chatted. He asked me what I was doing, and I explained to him what I was doing. He became extraordinarily excited. He said, "It's fantastic. It's extraordinary, that you could have found a way of applying, genuinely thinking of applying thermodynamics to something so different, and that you find everything will be decided upon analytic properties like partition function," and of course he understood instantly. 
And he asked me to give a lecture, and he said, "Make it a lecture in the evening, for the historians and the ladies." Those were his words. "Make it easy." 
So one evening, which was fixed with his secretary, I came up and I was expecting to find "historians and ladies." To my surprise, Oppenheimer was there. I tried to block his way, and he went, "No, I'm very much interested.' And then Von Neumann came. I said, "You know my story completely. I didn't prepare a lecture for you." "Well," he says, "perhaps not, but I'm the chairman and the discussion may be interesting." Now, the lecture was, again, to explain to this group that the kind of thinking represented by thermodynamics, as Tolman had made me understand it, could be applied outside and that in a way the abyss between, how to say, humanities and sciences was something you could bridge. That was Oppenheimer's idea, or something like it. 
Well, I saw all these great men and their spouses arriving, and my heart sank to my heels. I became totally incoherent. I had prepared a very simplified lecture, which I could not do at that age - I could do it now, perhaps, but not then. I tried to change it into a lecture for them. They started falling asleep and snoring. It was a horrible sight. I stopped after forty-five minutes saying, "Ladies and gentlemen, thank you for your attention," etc., etc. Mild applause. Von Neumann stands up and says, "Any questions?" Dead silence. Then a friend asked a question. "Any other question?" Dead silence. Another friend asked a question. And when Von Neumann was about to close the lecture, somebody named Otto Neumenbour stands up in the last row and says, "I have, not a question, but a statement. This is the worst lecture I have attended in my life. I have not understood one word the speaker said. I don't see any relation with the title," and he went on like that, until Oppenheimer stopped him. "Otto, Otto. Please, let me respond, if Dr Mandelbrot would be so kind as to allow me to respond instead for him. The title is very unfortunate. I gave it to my secretary. Dr Mandelbrot should have changed it to be more appropriate. As to the content, well, it may well be that he didn't make justice to his own work, but I believe I understand his every word, and he has a point." 
Now he went on into the celebrated Oppenheimer lecture. In fact he was the fear of any lecturer in physics - after he had struggled for an hour explaining things, Oppenheimer would stand up and say, "Well, if I understand correctly, this is what you said." In ten minutes he would speak flawlessly - finished sentences and everything! At that time everybody woke up. They said, "That miserable lecturer, he was trying to say these things!" Well, then when he sat down, Von Neumann stood up and said, "Well, I too have some comments to make about Dr Mandelbrot's lecture. We've had a number of interesting discussions and it may well be that he didn't do much justice to his work." Well, it was an abominable lecture, and he went on in his style which was very different, explaining what he saw in my work and why it was interesting, why this and that. Well, needless to say, I was taken in time by my friends to the only place in Princeton that served beer at that time. 
Next day I went to see to Neumenbour, when I entered he said, "Oh, I'm very sorry. I made a fool of myself yesterday. Please excuse me," etc., etc. (I replied) "No, I am coming to thank you. It was you, in a way, that started the real lecture." Well, so you see what was happening was that Von Neumann - and Oppenheimer, I think- understood what I was trying to do, and Von Neumann wanted to encourage me very strongly.
Note added: In this Caltech oral history, Delbruck recalls that at one point he was studying Fisher's The Genetical Theory of Natural Selection, and mentioned this to a visitor from the Rockefeller Foundation (the sponsor of Delbruck's fellowship at the time). He was immediately offered the chance to work with Fisher, but decided to go to Caltech (as a postdoc; he was hired back as a professor some years later) instead. Also, see comments for corrections to Mandelbrot's story from a biologist.

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?

Friday, April 17, 2020

The von Neumann-Fuchs bomb, and the radiation compression mechanism of Ulam-Teller-Sakharov


Some useful references below on the Ulam-Teller mechanism, Sakharov's Third Idea, and the von Neumann-Fuchs thermonuclear design of 1946. They resolve a mystery discussed previously on this blog:
Sakharov's Third Idea: ... If Zeldovich was already familiar with radiation pressure as the tool for compression, via the Fuchs report of 1948, then perhaps one cannot really credit Teller so much for adding this ingredient to Ulam's idea of a staged device using a fission bomb to compress the thermonuclear fuel. Fuchs and von Neumann had already proposed (and patented!) radiation implosion years before. More here.
It turns out that the compression mechanism used in the von Neumann-Fuchs design (vN is the first author on the patent application; the design was realized in the Operation Greenhouse George nuclear test of 1951) is not that of Ulam-Teller or Sakharov. In vN-F the D-T mixture reaches thermal equilibrium with ionized BeO gas, leading to a pressure increase of ~10x. This is not the "cold compression" via focused radiation pressure used in the U-T / Sakharov designs. That was, apparently,  conceived independently by Ulam-Teller and Sakharov.

It is only recently that the vN-F design has become public -- first obtained by the Soviets via espionage (Fuchs), and finally declassified and published by the Russians! It seems that Zeldovich had access to this information, but not Sakharov.

American and Soviet H-bomb development programmes: historical background by G. Goncharov.

John von Neumann and Klaus Fuchs: an Unlikely Collaboration by Jeremy Bernstein. See also here for some clarifying commentary.


A great anecdote:
Jeremy Bernstein: When I was an undergraduate at Harvard he [vN] came to the university to give lectures on the computer and the brain. They were the best lectures I have ever heard on anything — like mental champagne. After one of them I found myself walking in Harvard Square and looked up to see von Neumann. Thinking, correctly as it happened, that it would be the only chance I would have to ask him a question, I asked, ‘‘Professor von Neumann, will the computer ever replace the human mathematician?’’ He studied me and then responded, ‘‘Sonny, don’t worry about it.’’


Note added from comments: I hope this clarifies things a bit.
The question of how the Soviets got to the U-T mechanism is especially mysterious. Sakharov himself (ostensibly the Soviet inventor) was puzzled until the end about what had really happened! He did not have access to the vN-F design that has been made public from the Russian side (~2000, after Sakharov's death in 1989; still classified in US). Zeldovich and only a few others had seen the Fuchs information, at a time when the main focus of the Russian program was not the H bomb. Sakharov could never be sure whether his suggestion for cold radiation compression sparked Zeldovich's interest because the latter *had seen the idea before* without fully comprehending it. Sakharov wondered about this until the end of his life (see below), but I think his surmise was not correct: we know now that vN-F did *not* come up with that idea in their 1946 design. I've been puzzled about this question myself for some time. IF the vN-F design had used radiation pressure for cold compression, why did Teller get so much credit for replacing neutrons with radiation pressure in Ulam's staged design (1951)? I stumbled across the (now public) vN-F design by accident just recently -- I was reading some biographical stuff about Zeldovich which touched upon these issues.

https://infoproc.blogspot.com/2012/10/sakharovs-third-idea.html

Consider the following words in Sakharov’s memoirs, with a note he added toward the end of life:

Now I think that the main idea of the H-bomb design developed by the Zeldovich group was based on intelligence information. However, I can’t prove this conjecture. It occurred to me quite recently, but at the time I just gave it no thought. (Note added July 1987. David Holloway writes in “Soviet Thermonuclear Development,” International Security 4:3 (1979/80), p. 193: “The Soviet Union had been informed by Klaus Fuchs of the studies of thermonuclear weapons at Los Alamos up to 1946. … His information would have been misleading rather than helpful, because the early ideas were later shown not to work.” Therefore my conjecture is confirmed!)
Another useful resource: Gennady Gorelik (BU science historian): The Paternity of the H-Bombs: Soviet-American Perspectives
Teller, 1952, August (re Bethe’s Memorandum): The main principle of radiation implosion was developed in connection with the thermonuclear program and was stated at a con­ference on the thermonuclear bomb, in the spring of 1946. Dr. Bethe did not attend this conference, but Dr. Fuchs did. [ Original development by vN? ]

It is difficult to argue to what extent an invention is accidental: most difficult for someone who did not make the invention himself. It appears to me that the idea was a relatively slight modification of ideas generally known in 1946. Essentially only two elements had to be added: to implode a bigger volume, and, to achieve greater compression by keeping the imploded material cool as long as possible.
The last part ("cool as long as possible") refers to the fundamental difference between the vN-Fuchs design and the U-T mechanism of cold radiation compression. The former assumes thermal equilibrium between ionized gas and radiation, while latter deliberately avoids it as long as possible.

Official Soviet History: On the making of the Soviet hydrogen (thermonuclear) bomb, Yu B Khariton et al 1996 Phys.-Usp. 39 185. Some details on the origin of the compression idea, followed by the use of radiation pressure (Zeldovich and Sakharov).

Thursday, February 03, 2011

Berkeley photos

I had dinner on the north side. Bongo Burger, Top Dog, LaVal's, and some of the Asian restaurants seem to have survived 20+ years of competition :-)





When I was a student here they sometimes ran an ad (soliciting alumni support) in the Daily Californian showing that Berkeley had more Nobel Laureates than the entire USSR. I suppose the lab (now Lawrence Berkeley National Lab) might also, depending on how you count.



The Center for Theoretical Physics on campus. Early atomic bomb calculations were done on this floor of LeConte Hall by Oppenheimer, Teller and Bethe.

Sunday, July 31, 2011

What is the difference?

Some excerpts from a talk by Richard Hamming (inventor of, among other things, Hamming codes) on how to do great research. I recommend reading the whole thing!
You and Your Research: ... At Los Alamos I was brought in to run the computing machines which other people had got going, so those scientists and physicists could get back to business. I saw I was a stooge. I saw that although physically I was the same, they were different. And to put the thing bluntly, I was envious. I wanted to know why they were so different from me. I saw Feynman up close. I saw Fermi and Teller. I saw Oppenheimer. I saw Hans Bethe: he was my boss. I saw quite a few very capable people. I became very interested in the difference between those who do and those who might have done.

When I came to Bell Labs, I came into a very productive department. Bode was the department head at the time; Shannon was there, and there were other people. I continued examining the questions, ``Why?'' and ``What is the difference?'' I continued subsequently by reading biographies, autobiographies, asking people questions such as: ``How did you come to do this?'' I tried to find out what are the differences. And that's what this talk is about.

... How about having lots of `brains?' It sounds good. Most of you in this room probably have more than enough brains to do first-class work. But great work is something else than mere brains. Brains are measured in various ways. In mathematics, theoretical physics, astrophysics, typically brains correlates to a great extent with the ability to manipulate symbols. And so the typical IQ test is apt to score them fairly high. On the other hand, in other fields it is something different. For example, Bill Pfann, the fellow who did zone melting, came into my office one day. He had this idea dimly in his mind about what he wanted and he had some equations. It was pretty clear to me that this man didn't know much mathematics and he wasn't really articulate. His problem seemed interesting so I took it home and did a little work. I finally showed him how to run computers so he could compute his own answers. I gave him the power to compute. He went ahead, with negligible recognition from his own department, but ultimately he has collected all the prizes in the field. Once he got well started, his shyness, his awkwardness, his inarticulateness, fell away and he became much more productive in many other ways. Certainly he became much more articulate.

And I can cite another person in the same way. I trust he isn't in the audience, i.e. a fellow named Clogston. I met him when I was working on a problem with John Pierce's group and I didn't think he had much. I asked my friends who had been with him at school, ``Was he like that in graduate school?'' ``Yes,'' they replied. Well I would have fired the fellow, but J. R. Pierce was smart and kept him on. Clogston finally did the Clogston cable. After that there was a steady stream of good ideas. One success brought him confidence and courage.

One of the characteristics of successful scientists is having courage. Once you get your courage up and believe that you can do important problems, then you can. If you think you can't, almost surely you are not going to. Courage is one of the things that Shannon had supremely. You have only to think of his major theorem. He wants to create a method of coding, but he doesn't know what to do so he makes a random code. Then he is stuck. And then he asks the impossible question, ``What would the average random code do?'' He then proves that the average code is arbitrarily good, and that therefore there must be at least one good code. Who but a man of infinite courage could have dared to think those thoughts? That is the characteristic of great scientists; they have courage. They will go forward under incredible circumstances; they think and continue to think.

... Now for the matter of drive. You observe that most great scientists have tremendous drive. I worked for ten years with John Tukey at Bell Labs. He had tremendous drive. One day about three or four years after I joined, I discovered that John Tukey was slightly younger than I was. John was a genius and I clearly was not. Well I went storming into Bode's office and said, ``How can anybody my age know as much as John Tukey does?'' He leaned back in his chair, put his hands behind his head, grinned slightly, and said, ``You would be surprised Hamming, how much you would know if you worked as hard as he did that many years.'' I simply slunk out of the office!

What Bode was saying was this: ``Knowledge and productivity are like compound interest.'' Given two people of approximately the same ability and one person who works ten percent more than the other, the latter will more than twice outproduce the former. The more you know, the more you learn; the more you learn, the more you can do; the more you can do, the more the opportunity - it is very much like compound interest. I don't want to give you a rate, but it is a very high rate. Given two people with exactly the same ability, the one person who manages day in and day out to get in one more hour of thinking will be tremendously more productive over a lifetime. I took Bode's remark to heart; I spent a good deal more of my time for some years trying to work a bit harder and I found, in fact, I could get more work done. I don't like to say it in front of my wife, but I did sort of neglect her sometimes; I needed to study. You have to neglect things if you intend to get what you want done. There's no question about this. ...
I found this transcript via a discussion of learning and spaced repetition.

Sunday, March 01, 2020

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.

Thursday, August 09, 2012

Gell-Mann, Feynman, Everett

This site is a treasure trove of interesting video interviews -- including with Francis Crick, Freeman Dyson, Sydney Brenner, Marvin Minsky, Hans Bethe, Donald Knuth, and others. Many of the interviews have transcripts, which are much faster to read than listening to the interviews themselves.

Here's what Murray Gell-Mann has to say about quantum foundations:
In '63…'64 I worked on trying to understand quantum mechanics, and I brought in Felix Villars and for a while some comments... there were some comments by Dick Feynman who was nearby. And we all agreed on a rough understanding of quantum mechanics and the second law of thermodynamics and so on and so on, that was not really very different from what I'd been working on in the last ten or fifteen years.

I was not aware, and I don't think Felix was aware either, of the work of Everett when he was a graduate student at Princeton and worked on this, what some people have called 'many worlds' idea, suggested more or less by Wheeler. Apparently Everett was, as we learned at the Massagon [sic] meeting, Everett was an interesting person. He… it wasn't that he was passionately interested in quantum mechanics; he just liked to solve problems, and trying to improve the understanding of quantum mechanics was just one problem that he happened to look at. He spent most of the rest of his life working for the Weapon System Evaluation Group in Washington, WSEG, on military problems. Apparently he didn't care much as long as he could solve some interesting problems! [Some of these points, concerning Everett's life and motivations, and Wheeler's role in MW, are historically incorrect.]

Anyway, I didn't know about Everett's work so we discovered our interpretation independent of Everett. Now maybe Feynman knew about… about Everett's work and when he was commenting maybe he was drawing upon his knowledge of Everett, I have no idea, but… but certainly Felix and I didn't know about it, so we recreated something related to it.

Now, as interpreted by some people, Everett's work has two peculiar features: one is that this talk about many worlds and equally… many worlds equally real, which has confused a lot of people, including some very scholarly students of quantum mechanics. What does it mean, 'equally real'? It doesn't really have any useful meaning. What the people mean is that there are many histories of the… many alternative histories of the universe, many alternative course-grained, decoherent histories of the universe, and the theory treats them all on an equal footing, except for their probabilities. Now if that's what you mean by equally real, okay, but that's all it means; that the theory treats them on an equal footing apart from their probabilities. Which one actually happens in our experience, is a different matter and it's determined only probabilistically. Anyway, there's considerable continuity between the thoughts of '63-'64 and the thoughts that, and… and maybe earlier in the ‘60s, and the thoughts that Jim Hartle and I have had more recently, starting around '84-'85.
Indeed, Feynman was familiar with Everett's work -- see here and here.

Where Murray says "it's determined only probabilistically" I would say there is a subjective probability which describes how surprised one is to find oneself on a particular decoherent branch or history of the overall wavefunction -- i.e., how likely or unlikely we regard the outcomes we have observed to have been. For more see here.

Murray against Copenhagen:
... although the so-called Copenhagen interpretation is perfectly correct for all laboratory physics, laboratory experiments and so on, it's too special otherwise to be fundamental and it sort of strains credulity. It's… it’s not a convincing fundamental presentation, correct though… though it is, and as far as quantum cosmology is concerned it's hopeless. We were just saying, we were just quoting that old saw: describe the universe and give three examples. Well, to apply the… the Copenhagen interpretation to quantum cosmology,  you'd need a physicist outside the universe making repeated experiments, preferably on multiple copies of the universe and so on and so on. It's absurd. Clearly there is a definition to things happening independent of human observers. So I think that as this point of view is perfected it should be included in… in teaching fairly early, so that students aren't convinced that in order to understand quantum mechanics deeply they have to swallow some of this…very… some of these things that are very difficult to believe. But in the end of course, one can use the Copenhagen interpretations perfectly okay for experiments.

Thursday, March 21, 2013

He is a second Dirac, only this time human

Another historical letter sent by a reader. My understanding is that Feynman was not appointed at Berkeley because of Birge's anti-semitism: "One Jew (Oppenheimer) is enough," he is reported to have said.

CONFIDENTIAL

November 4, 1943

Professor R. T. Birge
Chairman, Department of Physics
University of California
Berkeley, California

Dear Professor Birge:

In these war times it is not always easy to think constructively about the peace that is to follow, even in such relatively small things as the welfare of our department. I would like to make one suggestion to you which concerns that, and about which I have myself a very sure and strong conviction.

As you know, we have quite a number of physicists here, and I have run into a few who are young and whose qualities I had not known before. Of these there is one who is in every way so outstanding and so clearly recognized as such, that I think it appropriate to call his name to your attention, with the urgent request that you consider him for a position in the department at the earliest time that that is possible. You may remember the name because he once applied for a fellowship in Berkeley: it is Richard Feynman. He is by all odds the most brilliant young physicist here, and everyone knows this. He is a man of thoroughly engaging character and personality, extremely clear, extremely normal in all respects, and an excellent teacher with a warm feeling for physics in all its aspects. He has the best possible relations both with the theoretical people of whom he is one, and with the experimental people with whom he works in very close harmony.

The reason for telling you about him now is that his excellence is so well known, both at Princeton where he worked before he came here, and to a not inconsiderable number of "big shots" on this project, that he has already been offered a position for the post war period, and will most certainly be offered others. I feel that he would be a great strength for our department, tending to tie together its teaching, its research and its experimental and theoretical aspects. I may give you two quotations from men with whom he has worked. Bethe has said that he would rather lose any two other men than Feyman from this present job, and Wigner said, "He is a second Dirac, only this time human."

Of course, there are several people here whose recommendation you might want; in the first instance Professors Brode and McMillan. I hope you will not mind my calling this matter to your attention, but I feel that if we can follow the suggestion I have made, all of us will be very happy and proud about it in the future. I cannot too strongly emphasize Feynman's remarkable personal qualities which have been generally recognized by officers, scientists and laity in this community.

With every good wish,

Robert Oppenheimer

Friday, March 26, 2021

John von Neumann, 1966 Documentary

 

This 1966 documentary on von Neumann was produced by the Mathematical Association of America. It includes interviews with Wigner, Ulam, Halmos, Goldstine, and others. 

At ~34m Bethe (leader of the Los Alamos theory division) gives primary credit to vN for the implosion method in fission bombs. While vN's previous work on shock waves and explosive lenses is often acknowledged as important for solving the implosion problem, this is the first time I have seen him given credit for the idea itself. Seth Neddermeyer's Enrico Fermi Award citation gives him credit for "invention of the implosion technique" and the original solid core design was referred to as the "Christy gadget" after Robert Christy. As usual, history is much more complicated than the simplified narrative that becomes conventional.
Teller: He could and did talk to my three-year-old son on his own terms and I sometimes wondered whether his relations to the rest of us were a little bit similar.
A recent application of vN's Quantum Ergodic Theorem: Macroscopic Superposition States in Isolated Quantum Systems.

Cloning vN (science fiction): short story, longer (AI vs genetic engineering).

Sunday, August 15, 2010

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.

Thursday, January 24, 2013

Learn to solve every problem that has been solved

Feynman had that on his final blackboard. Crazy? Even for Feynman? An admirable ambition, nonetheless.

At what point did this become impossible for even the smartest human alive? What if we amend it to Learn to solve every important problem that has been solved? (For some threshold of importance...)




Feynman's TO LEARN list:

Bethe Ansatz, Kondo Effect, 2-D Hall Effect, "accel. temp" = Unruh Effect?, Non-linear classical Hydrodynamics

Do I know anyone well-acquainted with all of these topics? I can think of a few people who come close ...

While it may be impossible to achieve Feynman's goal, I'm surprised that more people don't attempt the importance-threshold modified version. Suppose we set the importance bar really, really high: what are the most important results that everyone should try to understand? Here's a very biased partial list: basic physics and mathematics (e.g., to the level of the Feynman Lectures); quantitative theory of genetics and evolution; information, entropy and probability; basic ideas about logic and computation (Godel and Turing?); ... What else? Dynamics of markets? Complex Systems? Psychometrics? Descriptive biology? Organic chemistry?

Friday, September 01, 2017

Lax on vN: "He understood in an instant"



Mathematician Peter Lax (awarded National Medal of Science, Wolf and Abel prizes), interviewed about his work on the Manhattan Project. His comments on von Neumann and Feynman:
Lax: ... Von Neumann was very deeply involved in Los Alamos. He realized that computers would be needed to carry out the calculations needed. So that was, I think, his initial impulse in developing computers. Of course, he realized that computing would be important for every highly technical project, not just atomic energy. He was the most remarkable man. I’m always utterly surprised that his name is not common, household.

It is a name that should be known to every American—in fact, every person in the world, just as the name of Einstein is. I am always utterly surprised how come he’s almost totally unknown. ... All people who had met him and interacted with him realized that his brain was more powerful than anyone’s they have ever encountered. I remember Hans Bethe even said, only half in jest, that von Neumann’s brain was a new development of the human brain. Only a slight exaggeration.

... People today have a hard time to imagine how brilliant von Neumann was. If you talked to him, after three words, he took over. He understood in an instant what the problem was and had ideas. Everybody wanted to talk to him.

...

Kelly: I think another person that you mention is Richard Feynman?

Lax: Yes, yes, he was perhaps the most brilliant of the people there. He was also somewhat eccentric. He played the bongo drums. But everybody admired his brilliance. [ vN was a consultant and only visited Los Alamos occasionally. ]
Full transcript. See also Another species, an evolution beyond man.

Saturday, August 31, 2013

Another species, an evolution beyond man




Readers might be interested in this interview I did, which is on the MIRI (Machine Intelligence Research Institute, in Berkeley) website. Some excerpts below.
... I think there is good evidence that existing genetic variants in the human population (i.e., alleles affecting intelligence that are found today in the collective world population, but not necessarily in a single person) can be combined to produce a phenotype which is far beyond anything yet seen in human history. This would not surprise an animal or plant breeder — experiments on corn, cows, chickens, drosophila, etc. have shifted population means by many standard deviations (e.g., +30 SD in the case of corn).

... I think we already have some hints in this direction. Take the case of John von Neumann, widely regarded as one of the greatest intellects in the 20th century, and a famous polymath. He made fundamental contributions in mathematics, physics, nuclear weapons research, computer architecture, game theory and automata theory.

In addition to his abstract reasoning ability, von Neumann had formidable powers of mental calculation and a photographic memory. In my opinion, genotypes exist that correspond to phenotypes as far beyond von Neumann as he was beyond a normal human.

I have known a great many intelligent people in my life. I knew Planck, von Laue and Heisenberg. Paul Dirac was my brother in law; Leo Szilard and Edward Teller have been among my closest friends; and Albert Einstein was a good friend, too. But none of them had a mind as quick and acute as Jansci [John] von Neumann. I have often remarked this in the presence of those men and no one ever disputed me. – Nobel Laureate Eugene Wigner

You know, Herb, how much faster I am in thinking than you are. That is how much faster von Neumann is compared to me. – Nobel Laureate Enrico Fermi to his former PhD student Herb Anderson.

One of his remarkable abilities was his power of absolute recall. As far as I could tell, von Neumann was able on once reading a book or article to quote it back verbatim; moreover, he could do it years later without hesitation. He could also translate it at no diminution in speed from its original language into English. On one occasion I tested his ability by asking him to tell me how The Tale of Two Cities started. Whereupon, without any pause, he immediately began to recite the first chapter and continued until asked to stop after about ten or fifteen minutes. – Herman Goldstine, mathematician and computer pioneer.

I always thought Von Neumann’s brain indicated that he was from another species, an evolution beyond man. – Nobel Laureate Hans A. Bethe.

The quantitative argument for why there are many SD's to be had from tuning genotypes is so simple that I'll summarize it here (see also, e.g., here or here).  Suppose variation in cognitive ability is

1. highly polygenic (i.e., controlled by N loci, where N is large; N is almost certainly more than 1k -- perhaps roughly 10k), and

2. approximately linear (note the additive heritability of g is larger than the non-additive part).

Then the population SD for the trait corresponds to an excess of roughly Sqrt(N) positive alleles. A genius like vN might be +6 SD, so would have roughly 6 Sqrt(N) more positive alleles than the average person (e.g., 200 extra positive alleles if N = 1000). But there are roughly +Sqrt(N) SDs in phenotype to be had by an individual who has essentially all of the N positive alleles. As long as Sqrt(N) >> 6, there is ample extant variation for selection to act on to produce a type superior to any that has existed before. (The probability of producing a "maximal type" through random breeding is ~ exp( - N), and for large N the historical human population is insufficient to have made this likely.)

This basic calculation underlies the work of animal and plant breeders, who have in many cases (corn, drosophila, cows, dogs) moved the "wild type" population by many SD through selection. See, e.g., this essay by famed geneticist James Crow of Wisconsin.

Tuesday, July 04, 2017

Building the Gadget: A Technical History of the Atomic Bomb


This is the best technical summary of the Los Alamos component of the Manhattan Project that I know of. It includes, for example, detail about the hydrodynamical issues that had to be overcome for successful implosion. That work drew heavily on von Neumann's expertise in shock waves, explosives, numerical solution of hydrodynamic partial differential equations, etc. A visit by G.I. Taylor alerted the designers to the possibility of instabilities in the shock front (Rayleigh–Taylor instability). Concern over these instabilities led to the solid-core design known as the Christy Gadget.
Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943-1945

... Unlike earlier histories of Los Alamos, this book treats in detail the research and development that led to the implosion and gun weapons; the research in nuclear physics, chemistry, and metallurgy that enabled scientists to design these weapons; and the conception of the thermonuclear bomb, the "Super." Although fascinating in its own right, this story has particular interest because of its impact on subsequent devel- opments. Although many books examine the implications of Los Alamos for the development of a nuclear weapons culture, this is the first to study its role in the rise of the methodology of "big science" as carried out in large national laboratories.

... The principal reason that the technical history of Los Alamos has not yet been written is that even today, after half a century, much of the original documentation remains classified. With cooperation from the Los Alamos Laboratory, we received authorization to examine all the relevant documentation. The book then underwent a classification review that resulted in the removal from this edition of all textual material judged sensitive by the Department of Energy and all references to classified documents. (For this reason, a number of quotations appear without attribution.) However, the authorities removed little information. Thus, except for a small number of technical facts, this account represents the complete story. In every instance the deleted information was strictly technical; in no way has the Los Alamos Laboratory or the Department of Energy attempted to shape our interpretations. This is not, therefore, a "company history"; throughout the research and writing, we enjoyed intellectual freedom.

... Scientific research was an essential component of the new approach: the first atomic bombs could not have been built by engineers alone, for in no sense was developing these bombs an ordinary engineering task. Many gaps existed in the scientific knowledge needed to complete the bombs. Initially, no one knew whether an atomic weapon could be made. Furthermore, the necessary technology extended well beyond the "state of the art." Solving the technical problems required a heavy investment in basic research by top-level scientists trained to explore the unknown - scientists like Hans Bethe, Richard Feynman, Rudolf Peierls, Edward Teller, John von Neumann, Luis Alvarez, and George Kistiakowsky. To penetrate the scientific phenomena required a deep understanding of nuclear physics, chemistry, explosives, and hydrodynamics. Both theoreticians and experimentalists had to push their scientific tools far beyond their usual capabilities. For example, methods had to be developed to carry out numerical hydrodynamics calculations on a scale never before attempted, and experimentalists had to expand the sensitivity of their detectors into qualitatively new regimes.

... American physics continued to prosper throughout the 1920s and1930s, despite the Depression. Advances in quantum theory stimulated interest in the microscopic structure of matter, and in 1923 Robert Millikan of Caltech was awarded the Nobel Prize for his work on electrons. In the 1930s and 1940s, Oppenheimer taught quantum theory to large numbers of students at the Berkeley campus of the University of California as well as at Caltech. Also at Berkeley in the 1930s and 1940s, the entrepreneurial Lawrence gathered chemists, engineers, and physicists together in a laboratory where he built a series of ever-larger cyclotrons and led numerous projects in nuclear chemistry, nuclear physics, and medicine. By bringing together specialists from different fields to work cooperatively on large common projects, Lawrence helped to create a distinctly American collaborative research endeavor - centered on teams, as in the industrial research laboratories, but oriented toward basic studies without immediate application. This approach flourished during World War II.

Friday, December 31, 2021

Happy New Year 2022!

Best wishes to everyone :-)

I posted this video some years ago, but it was eventually taken down by YouTube. I came across it today and thought I would share it again. 

The documentary includes interviews with Rabi, Ulam, Bethe, Frank Oppenheimer, Robert Wilson, and Dyson. 


 


Some other recommendations below. I recently re-listened to these podcasts and quite enjoyed them. The interview with Bobby covers brain mapping, neuroscience, careers in science, biology vs physics. With Ted we go deep into free will, parallel universes, science fiction, and genetic engineering. Bruno shares his insights on geopolitics -- the emerging multipolar world of competition and cooperation between the US, Russia, Europe, and China.









A hopeful note for 2022 and the pandemic:

I followed COVID closely at the beginning (early 2020; search on blog if interested). I called the pandemic well before most people, and even provided some useful advice to a few big portfolio managers as well as to Dom and his team in the UK government. But once I realized that 

the average level among political leaders and "public intellectuals" is too low for serious cost-benefit analysis,

I got bored of COVID and stopped thinking about it.

However with Omicron (thanks to a ping from Dom) I started to follow events again. Preliminary data suggest we may be following the evolutionary path of increased transmissibility but reduced lethality. 

The data from UK and SA already seem to strongly support this conclusion, although both populations have at least one of: high vaccination level / resistance from spread of earlier variants. Whether Omicron is "intrinsically" less lethal (i.e., to a population such as the unvaccinated ~40% of the PRC population that has never been exposed to COVID) remains to be seen but we should know within a month or so.

If, e.g., Omicron results in hospitalization / death at ~1/3 the rate of earlier variants, then we will already be in the flu-like range of severity (whereas original COVID was at most like a ~10x more severe flu). In this scenario rational leaders should just go for herd immunity (perhaps with some cocooning of vulnerable sub-populations) and get it over with.

I'll be watching some of the more functional countries like S. Korea, PRC, etc. to see when/if they relax their strict lockdown and quarantine policies. Perhaps there are some smaller EU countries to keep an eye on as well.

Blog Archive

Labels