The sun shone brilliantly, the air was crisp and heady, and it was warm even though there was a lot of snow on the ground — a lovely contrast to the rigors of winter in Madison. Calkin drove us into Santa Fe, and we stopped for lunch at the Hotel La Fonda, where we sat at the low Spanish-style tables in the bar. After an interesting New-Mexico-style meal, we walked to a small doorway in a one-story building on a little street that bordered the central Plaza. In a modest suite of rooms, a smiling middle-aged lady invited me to fill out a few forms, turned a crank on a primitive desk machine, and produced the sheets of paper that were our passes to the Los Alamos Project. This inconspicuous little office was the entrance to the gigantic Los Alamos complex. The scene, very much like a British cloak-and-dagger mystery, brought memories of my boyhood fascination with such tales.
The project site was about forty miles northwest of Santa Fe. The ride was hair-raising, Jack having elected to show us the countryside by taking us on a short cut — a muddy track through sparse Mexican and Indian villages — until we came to the Rio Grande, which we crossed on a narrow wooden bridge.
The setting was romantic. We were going up and up into a strange, mysterious landscape of mesas, cliffs, piñon trees and brush. This became a forest of pines as we gained elevation. At a military gate in a barbed-wire fence, we showed our passes and drove on to a helter-skelter collection of one- and two-story wooden structures built along muddy, unpaved, narrow streets and paths.
We were assigned a small cottage by a pond (with the promise of larger quarters as soon as they were built). I then followed Jack to my first visit to the technical area.
We entered an office, where I was surprised to find Johnny deep in conversation with a man of middle stature, bushy eyebrows, an intense expression. He limped slightly as he paced back and forth in front of a blackboard. This was Edward Teller, to whom Johnny introduced me.
They were talking about things which I only vaguely understood. There were tremendously long formulae on the blackboard, which scared me. Seeing all these complications of analysis, I was dumbfounded, fearing I would never be able to contribute anything. However, when day after day the same equations remained and were not changed every few hours as I had expected, I regained my confidence and some hope of being able to add something to the theoretical work.
I understood snatches of their conversation, and an hour later, Johnny took me aside and explained to me formally and clearly the nature of the project and its status at the moment. The work in Los Alamos had started in earnest only about two or three months before. Von Neumann seemed very certain of its importance and radiated confidence about the ultimate success of the enterprise whose objective was the construction of an atomic bomb. He told me of all the possibilities which had been considered, of the problems relating to the assembling of fissionable materials, about plutonium (which did not yet physically exist even in the most microscopic quantities at Los Alamos). I remember very well, when a couple of months later I saw Robert Oppenheimer running excitedly down a corridor holding a small vial in his hand, with Victor Weisskopf trailing after him. He was showing some mysterious drops of something at the bottom of the vial. Doors opened, people were summoned, whispered conversations ensued, there was great excitement. The first quantity of plutonium had just arrived at the lab.
Needless to say, I soon ran across most of the Wisconsinites who had so mysteriously disappeared from Madison before us. I met Hans Bethe on the first day. I knew more about him than about Teller. I gradually met the entire group of theoretical and experimental physicists. I had known many mathematicians in Europe and in this country, but not as many physicists.
I had some knowledge of theoretical physics, despite the joke I had told Johnny about my not understanding even the autocatalytic action of a toilet. Astronomy, of course, had been my first interest, and then physics and mathematics. I had even given a course in classical mechanics at Harvard, but it is one thing to know about physics abstractly, and quite another to have a practical encounter with problems directly connected with experimental data, such as the very novel technology which was to come from Los Alamos.
I found out that the main ability to have was a visual, and also an almost tactile, way to imagine the physical situations, rather than a merely logical picture of the problems.
The feeling for problems in physics is quite different from purely theoretical mathematical thinking. It is hard to describe the kind of imagination that enables one to guess at or gauge the behavior of physical phenomena. Very few mathematicians seem to possess it to any great degree. Johnny, for example, did not have to any extent the intuitive common sense and "gut" feeling or penchant for guessing what happens in given physical situations. His memory was mainly auditory, rather than visual.
Another thing that seems necessary is the knowledge of a dozen or so physical constants, not merely of their numerical value, but a real feeling for their relative orders of magnitude and interrelations, and, so to speak, an instinctive ability to "estimate."
I knew, of course, the values of constants like the velocity of light and maybe three or four other fundamental constants — the Planck constant h, a gas constant R, etc. Very soon I discovered that if one gets a feeling for no more than a dozen other radiation and nuclear constants, one can imagine the subatomic world almost tangibly, and manipulate the picture dimensionally and qualitatively, before calculating more precise relationships.
Most of the physics at Los Alamos could be reduced to the study of assemblies of particles interacting with each other, hitting each other, scattering, sometimes giving rise to new particles. Strangely enough, the actual working problems did not involve much of the mathematical apparatus of quantum theory although it lay at the base of the phenomena, but rather dynamics of a more classical kind — kinematics, statistical mechanics, large-scale motion problems, hydrodynamics, behavior of radiation, and the like. In fact, compared to quantum theory the project work was like applied mathematics as compared with abstract mathematics. If one is good at solving differential equations or using asymptotic series, one need not necessarily know the foundations of function space language. It is needed for a more fundamental understanding, of course. In the same way, quantum theory is necessary in many instances to explain the data and to explain the values of cross sections. But it was not crucial, once one understood the ideas and then the facts of events involving neutrons reacting with other nuclei.
Teller, in whose group I was supposed to work, talked to me on that first day about a problem in mathematical physics that was part of the necessary theoretical work in preparation for developing the idea of a "super" bomb, as the proposed thermonuclear hydrogen bomb was then called. The idea of thermonuclear reactions that would release enormous amounts of energy was, of course, older. Their role in the reactions in the interior of stars was discussed in theoretical papers in the 1930s by the physicists Geoffrey S. Atkinson and Fritz Houtermans. The idea of using a uranium fission explosion to trigger a thermonuclear reaction can be credited to Teller, Bethe, Konopinski, I believe, and perhaps some others.
Teller's problem concerned the interaction of an electron gas with radiation, and it had more to do with the thermonuclear possibilities than with the assembly of the fission bomb, which was the main problem and work of Los Alamos. He guessed a formula for energy transfers connected with the so-called Compton effect about the rate of energy transfer. This formula, based on dimensional grounds and his intuition alone, was quite simple; he asked me to try to derive it more rigorously. As it was presented, there was no numerical factor in front. This seemed curious to me. I asked him explicitly about this a day or two later, and he said "Oh, the factor should be 1."