My tremendous luck was to be the only person who had spent six months listening to Feynman expounding his new ideas at Cornell and then spent six weeks listening to Schwinger expounding his new ideas in Ann Arbor. They were both explaining the same experiments, which measure radiation interacting with atoms and electrons. But the two ways of explaining the experiments looked totally different, Feynman drawing little pictures and Schwinger writing down complicated equations. The flash of illumination on the Greyhound bus gave me the connection between the two explanations, allowing me to translate one into the other.
As a result, I had a simpler description of the explanations, combining the advantages of Schwinger and Feynman.
At the end of a week I took a bus once again, this time a thirty-hour trip, via Pittsburgh and Philadelphia. It was a fine journey, the first day being spent crossing the plains of Indiana and Ohio, which are an endless succession of rich well-tended farms and rich ill-tended industrial cities. At nightfall we crossed the Ohio River and rose rapidly into the mountains of Pennsylvania. At midnight we reached Pittsburgh, the great steel city which produces as much steel as the entire USSR. It really is impressive, with its soot and its glare of lights and furnaces. Pittsburgh is on the Ohio River, its port is Cleveland, and it belongs to the Midwest; it is only a historical accident that it is included in Pennsylvania rather than Ohio. Between it and Philadelphia lie two hundred miles of sparsely inhabited mountains. So in a desperate attempt to hold Pennsylvania together, Pittsburgh and Philadelphia were joined by the Pennsylvania Turnpike, the most ambitious road-building project in the country. We were lucky to drive along the turnpike on our route. It is a magnificent drive, through rugged forest scenery; the road is built so that no traffic ever crosses it (it all goes under or over), and in the rare places where other roads join it, they have complete cloverleaf junctions. When it comes to a big mountain, the turnpike just goes through it. The sun rose when we were halfway along the turnpike, and so we saw it at its loveliest. About Philadelphia, the city of brotherly love, there is little to be said. It is an ugly place. A short ride from Philadelphia, across rolling downs and meadows, brought us finally to Princeton, which is a pleasant little old town, entirely supported by the university, and not in the least American-looking.
The university is a large collection of buildings, built in a solid gothic style in imitation of Oxford and Cambridge, in the centre of the town. The institute is a small building in the country, about a mile from the university, built in an unpretentious and utilitarian red brick. The pleasant surprise is that it is small and intimate, a good deal smaller than the physics building at Cornell. The institute is beautifully decorated and furnished. There is a lounge with the Times air edition and every other important newspaper and periodical, an excellent specialist library, a tea room, and private work rooms. I glowed with reflected glory as I walked past the doors bearing the names of Einstein, Weyl, von Neumann, and Gödel. I have been given a beautiful mahogany table in a beautifully carpeted room next door to Oppenheimer, where his five young physicists are put, to be near him and one another. I have not yet met my colleagues. When I visited the institute, there were more children there than grown-ups, Dirac with his family shortly leaving for England, and various other children playing cowboys and Indians, and von Neumann looking rather vague in the midst of the confusion. If I don’t do well here, it won’t be the institute’s fault.
The Dirac children in Princeton were his two biological daughters, roughly ten years younger than the stepchildren whom I had met in Cambridge.
Oppenheimer will not be here for about a month. At the moment he, with most of the other important people, is in England conferring with Canadian and British scientists on the subject of secrecy. The conference was held, according to the announcement, “in view of recent technical developments in atomic energy.” One may speculate as to whether this may mean (a) progress in achieving uranium power plants or (b) progress in achieving superbomb explosions. In the first case one would expect some loosening of secrecy, in the second some tightening. We shall see. After this he will be at the Solvay Conference at Brussels. The Solvay Conferences are the leading international physics conferences. They are always held at Brussels, and admission is by invitation only. You will probably hear about it in the newspapers.
Tomorrow will be exactly a year since I landed. What a tremendous success the year has been! Who would have dreamed that I should be coming to Princeton with the thought not of learning but of teaching Oppenheimer about physics? I had better be careful.
• 6 •
DEMIGODS ON STILTS
“Princeton is a quaint and ceremonious village, peopled by demigods on stilts.”
—EINSTEIN, in a letter to the queen of Belgium after he arrived in Princeton in 1933
THE LETTERS in this chapter were written from the Institute for Advanced Study in Princeton, except for one from Boston.
In 1948 Hideki Yukawa was the most famous Japanese physicist. In 1935 he had published the first field theory of nuclear forces, based on the conjectured existence of a new massive particle, the meson. During the war he remained at Kyoto as professor, not engaged in war work, teaching and taking care of students. In 1946 he started a new English-language journal, Progress in Theoretical Physics and succeeded in publishing it in the chaotic conditions of postwar Japan. The early issues of the journal contained amazing work done by Japanese physicists during the war when they were totally isolated from the rest of the world. Yukawa mailed copies of the early issues to Oppenheimer and other leading physicists, to let them know that Japanese science was still alive. Oppenheimer invited Yukawa to the Princeton institute in 1948, and mesons were produced experimentally in Berkeley in the same year. Yukawa won the Nobel Prize in Physics in 1949 for his prediction of the meson.
SEPTEMBER 26, 1948
Yukawa has turned up and is most friendly and approachable. We are hoping to get him to talk to a seminar before long. Besides him, there are few eminent people but a lot of good young ones. They are all struggling to understand the Schwinger radiation theory. I have not told them that I have been struggling to supersede it; that would be bad manners. I am planning to publish my bombshell as soon as possible, preferably before Oppenheimer comes to pull it to pieces, and meanwhile say as little as possible.
SEPTEMBER 30, 1948
After a brief visit to Cornell to collect my belongings, I settled down to work at writing up the physical theories I mentioned in the last letter. I was for five days stuck in my rooms, writing and thinking with a concentration which nearly killed me. On the seventh day the paper was complete, and with immense satisfaction I wrote the number 52 at the bottom of the last page. While I was struggling to get these ideas into shape, I thought they were so difficult I should never make them intelligible; however, reading the paper through after it was done, it seemed so simple and clear as hardly to be worth the effort expended on it. It is impossible for me to judge at present whether the work is as great as I think it may be. All I know is, it is certainly the best thing I have done yet.
My big paper is now finished, and I have recovered from the ordeal of writing it. Meanwhile I had a letter from Bethe inviting me to spend a day at Columbia and tell the people there about the work. I am going up tomorrow morning and will probably have an all-day session discussing these problems, just as we used to in the old days at Cornell. One thing I have discovered since I wrote the paper. I was trying to keep it as short as possible, so there are questions and developments which I avoided mentioning so as to keep the argument simple. I shall now be able to write a whole string of papers going into these various points, so I shall have no lack of subject matter for my work for the next few months. To arrive at the frontiers of physics is like breaking through a crust, after which one finds plenty of room to move in a lot of directions.
Next piece of news; I have been offered the job of chief assistant at Greenwich Observatory, with excellent prospects of being Astronomer Royal
by about 1965, and have decided to turn it down. I had a long letter about this from a man called Atkinson, the present senior chief assistant and heir presumptive. He gave me all possible information about the position, painting in glowing terms the scenery and architecture of Herstmonceux. It is a strange irony that this should happen; I wonder what I should have said at the age of eight if I had been told I should one day refuse such a job. You can imagine the reasons I shall give for not applying for the position. Fundamentally, I have fallen in love with the most modern part of physics and cannot now leave go of it. During the next five years, there is a gambler’s chance of my doing something substantial in this field, but only if I give it a lot of my time and attention. The important thing is to use this chance while it is here. By the time I am forty, the game will be played out. I have quite a high opinion of my ability to do most things, but one thing I know I can’t do, and that is to work like Einstein in isolation and produce epoch-making work. And that is what I should have to do if I were at Herstmonceux.
One thing which I must always keep in mind to prevent me from getting too conceited is that I was extraordinarily lucky over the piece of work I have just finished. The work consisted of a unification of radiation theory, combining the advantageous features of the two theories put forward by Schwinger and Feynman. It happened that I was the only young person in the world who had worked with the Schwinger theory from the beginning and had also had long personal contact with Feynman at Cornell, so I had a unique opportunity to put the two together. I should have had to be rather stupid not to have put the two together. It is for the sake of opportunities like this that I want to spend five more years poor and free rather than as a well-paid civil servant.
OCTOBER 4, 1948
On Friday I went to New York and was welcomed by Bethe, who was as friendly and informal as ever. He talked a good deal about what he had seen in Europe and all my acquaintances he had met. He said the places where most physics was being done were Zürich, Bristol, and Birmingham. At Cambridge, he said, there was still the same lot of people displaying the same masterly inactivity. One message he brought was from [Nevill] Mott at Bristol offering me a good job as lecturer there, with expectations of a professorship soon. This is certainly much more in my line than being an astronomer. However, my feeling about that too is that I shall have enough of my life being a professor and I need not be in any hurry to start.
Nevill Mott was the professor of theoretical physics at Bristol. Together with the experimentalist Cecil Powell, he made Bristol the most active center of physical research in England at that time.
Two interesting pieces of news I heard recently which show that England still can do pretty well in physics, even if it can’t build such big machines as they have here. First, the blotting paper technique for analysing organic chemicals, which I wrote about recently and which is called paper chromatography, was invented and first used at the Wool Industries Research Laboratories at Leeds, in the year 1944. These people used dyes to identify the various substances on their papers; hence the name. The use of tracers for this part of the work was suggested quite early, but Berkeley having one of the best radiochemical labs in the world has been the first to exploit it thoroughly. Second, attached to the institute here is an electronic computer project, which is aiming to be able to handle any conceivable problem. The technical side of it is under the Radio Corporation of America, and the general design is being looked after by von Neumann. The most important single technical problem in building such a machine is to make a “memory” for it, a device for storing numbers during a calculation so that they can be used later. The RCA has invented an instrument for this purpose called a selectron tube, which will hold a thousand digits and enable any particular one to be read and used in one-twenty-five-thousandth part of a second. The complete machine was to have had a memory unit with forty of these tubes. However, the project has been held up now for some time because after two years of intensive work, the RCA still could not get their tubes to work reliably. At this point there came a report from a man called Frederic Williams at Birmingham, describing a different and much simpler kind of tube which will do the same job. And within six weeks the RCA had built a tube from Williams’s specification and found that it worked satisfactorily. There is no doubt that the great fault of American science is overconcentration on fashionable fields. So long as there are in England a lot of odd groups of people working on odd things, they have nothing to fear from American competition.
I must tell you about my meeting with Gödel. There is not a great deal to be said about it, since we talked mainly about mathematics and physics; he is an amusing talker, and not so pathologically shy in his home as he is at the institute. He is a little man of about forty, with a fat little Austrian wife, and they live together seeing very little of anybody and will no doubt continue to do so for many years to come since he is a permanent member of the institute. The interesting thing to me was to learn what Gödel is doing and proposes to do in the way of research. He produced during his youth two epoch-making discoveries in pure mathematics, one in 1932 and one in 1939, and since then nothing has been heard from him. With the whole of mathematics to choose from and his unrivalled talents, I was curious to know what such a man would choose to do. The answer, when it came, was completely baffling. It turns out that he has spent the last few years working in physics, in collaboration with Einstein, on problems of general relativity.
Gödel had discovered some new solutions of Einstein’s equations of general relativity, describing rotating universes. The solutions known before Gödel’s discovery did not rotate. Gödel invited me to his home because he wanted to know whether there was any chance that one of his rotating solutions might be true. Were the observations of the real universe accurate enough to decide whether it was rotating or not? I knew enough about observational astronomy to answer his question. The answer was negative. The observations at that time were far from being accurate enough to detect visible effects of rotation. If Gödel had asked the question today, the answer would have been different. Since the microwave background radiation has been discovered and accurately measured, we have a far more precise understanding of the dynamics of the universe, and the Gödel solutions are now definitely excluded.
I will try to explain why this is baffling. In the first place, there is no question of Gödel suffering from deterioration of intellect; he understands general relativity and its position in physics as well as anybody and knows quite well what he is about. He has found some results which will certainly be of interest to specialists in relativity. On the other hand, it is clear to most people that general relativity is one of the least promising fields that one can think of for research at the present time. The theory is from a physical point of view completely definite and completely in agreement with all experiments. Most of the work that has been done on it recently has been done by mathematicians who were interested in the mathematics of it rather than the physics, and this work was not of much value to mathematics and still less to physics. The best papers on the subject in recent years have been those of Einstein, who has done some good things, but it was generally agreed that he was continuing work on it more as a hobby for his old age than in the hope of important new discoveries. It is the general view of physicists that the theory will remain much as it is until there are either some new experiments to upset it or a development from the direction of quantum theory to include it. In spite of all this, there is Gödel. Von Neumann, when he found himself in a similar situation, looking around for something to do worthy of his powers, went in for calculating machines in a big way. That one can understand; indeed it was a wise move.
OCTOBER 10, 1948
There is one consideration involved in this question of physics versus astronomy which I did not mention when I wrote before. It might have been supposed until recently that, as nuclear physics was a subject in which secrecy was having a seriously hampering effect on research, at least astronomy would have the ad
vantage of being free from this. However, it turns out that the kind of fundamental nuclear physics which I am doing at present is completely free and likely to remain so, since it is quite impracticable to use it for predicting the behaviour of matter in bulk. On the other hand, it is just in the borderline between physics and astronomy that the most delicate problems involved in constructing superpowerful atomic bombs arise, and in this field I imagine are the most jealously guarded secrets. A superbomb is probably more like a nova (new star) than anything else we can see, so the time may come when telescopes become more important military weapons than piles.
The fear that I felt, of astronomy becoming secret because of the connection between exploding stars and exploding hydrogen bombs, turned out to be unwarranted. Fortunately, the tricks that we use to make hydrogen bombs explode are quite different from the tricks that Nature uses to make stars explode. Secrecy is a problem for astronomers only if they are observing man-made objects close to the earth.
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