Quantum Man: Richard Feynman's Life in Science

by Lawrence M. Krauss

  Following his return to and debriefing at Princeton, he didn’t have to wait long before learning what was to come next. Oppenheimer had been chosen to lead the bomb project, and shortly after that he picked Los Alamos, New Mexico—a remote and starkly beautiful countryside where he had previously roamed as a younger man, and which also fit the army’s requirements of isolation and safety—as the site of what would soon become the most advanced laboratory in the world, with the highest concentration of brilliant scientists ever seen per square mile (even allowing, as John F. Kennedy once did, for those days when Thomas Jefferson dined alone in the White House).

  Oppenheimer was a brilliant scientist, but more important for the success of the atomic bomb project, he was an equally brilliant judge of talent in others. He quickly began to recruit and amass a team of outstanding colleagues to relocate to Los Alamos even before the laboratory and associated housing had been completed. Needless to say, he sought out Feynman, and did whatever he could to convince him to move to New Mexico with the first wave of scientists, at the end of March in 1943.

  Oppenheimer’s offer led to the other fortuitious impact that the war effort had on the married couple. Arline’s illness was progressing. She would live only two years following their marriage. The first years of any marriage should be a time, if there is ever going to be a time, of romance and adventure. Had the war not turned the world topsy-turvy, Feynman undoubtedly would have taken longer to finish his doctorate, he and Arline would have continued their strained existence in Princeton as her health deteriorated, and then, before she died, he might have proceeded to an assistant professorship in some place not that different than Princeton. Instead, his decision to move to the wild and unknown Southwest would give the young couple, especially Arline, the chance for a morsel of the romance and adventure that they had been longing for and that she otherwise would never have been able to enjoy.

  Feynman was touched by Oppenheimer’s concern and consideration. “Oppie,” as he was known to his colleagues, seemed to be the perfect leader for this group of independent-minded scientists. He commanded their respect—as Feynman later said, “We could discuss everything technically because he understood it all.” At the same time he showed uncommon concern about the well-being of each and every person he had recruited for this task. Again, as Feynman remembered it, “Oppenheimer was extremely human. When he was recruiting all these people to go to Los Alamos . . . he still worried about all the details. For example, when he asked me to come I told him I had this problem—that my wife had tuberculosis. He himself found a hospital and called me up to say they had found somewhere that would take care of her. I was only one of all the many people he was recruiting, but this was the way he always was, concerned with people’s individual problems.” Oppenheimer’s call from Chicago about finding a hospital for Arline was the first telephone call Feynman had received from so far away, perhaps one of the reasons he was so touched. In any case, after some negotiations with the army authorities, Arline and Richard were set to board the Santa Fe “Chief” from Chicago on March 30. Arline was beside herself with joy and excitement:

  Dearest Rich—if you only knew how happy you’ve made me with this train trip of ours—it’s all I’ve wanted and dreamed about since we’ve been married . . . with only one day left—I’m so excited and happy and bursting with joy—I think, eat, and sleep “you”—our life, our love, our marriage—the great future we are building. . . . If only tomorrow would hurry and come.

  At Arline’s urging, the two of them purchased a ticket for a private room, then they boarded the train and headed west. Ultimately, after exploring several possibilities, Arline was placed in a sanatorium in Albuquerque, one hundred miles from the laboratory site (there was no laboratory there yet), and Richard somehow made the trip to see her once a week.

  In one sense, Richard Feynman had been preparing for this experience his whole life. All of his talents were to be exploited during the next two years: his lightning computational abilities, his mathematical wizardry, his physical intuition, his clear appreciation for experiment, his disrespect for authority, his breadth of physics knowledge from nuclear physics to the physics of materials (shortly after arriving he became ill, and in a letter to his mother reported reading a chemical engineering textbook with topics ranging from “Transportation of Fluids” to “Distillation” while in the infirmary for three days), and his fascination with computing machines.

  The physics work was quite different from his academic work. It was easier than pushing the forefront into the unknown laws, but a lot dirtier than working on pristine single electrons in hydrogen atoms. Aside from his contributions to the development of the bomb, Feynman left little permanent scientific legacy from his work during this time. (There is a formula for the efficiency of a nuclear weapon, called the Bethe-Feynman formula, that is still used today, but that is about it.)

  Nevertheless, Los Alamos had a profound influence on Feynman’s career, and it all began by accident, as so many things do. Again, in his words: “Most of the big shots were out of town for one reason or the other, getting their furniture transferred or something. Except for Hans Bethe. It seems that when he was working on an idea he always liked to discuss it with someone. He couldn’t find anybody around, so he came down to my office . . . and he started to explain what he was thinking. When it comes to physics I forget exactly who I’m talking to, so I was saying, ‘No, no! That’s crazy!’ and so on. Whenever I objected, I was always wrong, but nevertheless that’s what he wanted.” As Bethe remembers it, “I knew nothing about him. . . . He had only recently got his Ph.D. from Wheeler, at Princeton. We got to talking, and he obviously was very bright. At the meetings and seminars he always asked questions which seemed particularly intelligent and penetrating. We began to collaborate together.” And in another reminiscence, “He was very lively from the beginning. . . . I realized very quickly that he was something phenomenal. . . . I thought Feynman perhaps the most ingenious man in the whole division, so we worked a great deal together.”

  The opportunity to work with Bethe at Los Alamos was fateful in the extreme. They complemented each other in remarkable ways, sharing uncanny physical intuition, mental stamina, and calculational ability. But Bethe was, in several other senses, everything that Feynman was not. He was calm and deliberate, and unlike the excitable Feynman, Bethe was “unflappable.” This was also reflected in their mathematical styles. Bethe began a calculation at the beginning, and ended at the end, no matter how long or difficult the road between was. Feynman, on the other hand, was as likely to begin in the middle or at the end, and jump back and forth until he had convinced himself he was right (or wrong). In other areas, Bethe served as a remarkable role model. Feynman loved his humor, his unaffected manner, and his straightforward and collegial way of dealing with others. And whereas Wheeler helped free up Feynman’s enthusiasm and creativity, he was not the physicist that Bethe was. If Feynman was to rise to new, and higher levels, he needed someone he could go head to head with. Bethe was the man.

  By the time Bethe had moved to Los Alamos, he had resolved one of the most important and vexing questions in astrophysics: how does the sun shine? For over a century scientists had wondered what energy process powers the sun so it has been able to shine with its observed luminosity for over 4 billion years. The earliest estimate, by a German doctor in the early eighteenth century, suggested that if the sun were a big ball of burning coal, it could burn with its observed brightness for about 10,000 years, which happened to be in nice accord with some biblical estimates of the age of the universe. Later in the century, two famous physicists, Heinrich Helmholtz and Lord Kelvin, estimated that the sun could be powered by the energy released during gravitational contraction, and this energy source could power the sun for perhaps 100 million years. However, even this estimate was far too low to explain what was by then the inferred age of the solar system—namely, billions, not hundreds of millions, o
f years.

  The mystery persisted through the 1920s, when the famous British astrophysicist Sir Arthur Stanley Eddington argued that there must be some unknown source of energy powering the solar interior. The problem was that model calculations of the sun’s profile suggested that the interior was no more than 10 million degrees in temperature, which is hot, but not that hot. In other words, the physical processes associated with the energies available at these temperatures were thought to be fairly well understood, with no room for new exotic physics. As a result, Eddington’s assertion was met with skepticism, leading him to utter his famous rebuke: “To those that think the temperature in the center of the Sun is not hot enough for some new physical process to take place, I say: Go and find a hotter place!”

  Bethe, who had studied with the greatest theoretical physicists in Europe, including Arnold Sommerfeld, Paul Dirac, and Enrico Fermi, had, by the early 1930s, established himself as perhaps the world’s foremost authority on the emerging field of nuclear physics. He wrote the definitive set of reviews in this field, which Feynman had studied while an undergraduate. If anyone was prepared to find the new process that powered the sun, it was Bethe, and in 1939 he made his great discovery. He realized that newly discovered nuclear reactions (similar in spirit to those later exploited in building the fission bomb, but instead of being based on breaking up heavy nuclei such as uranium and plutonium, these involved fusing light nuclei such as hydrogen into heavier nuclei) provided the key to releasing tremendous amounts of energy. Moreover, he showed that there was a series of reactions starting with protons, which make up the nuclei of hydrogen, and ultimately producing the nuclei of the next lightest element, helium, that would release more than twenty million times as much energy as comparable chemical reactions between hydrogen would release. While at a temperature of only 10 million degrees the average hydrogen nucleus might take over a billion years to experience a collision energetic enough to initiate such a reaction, over a hundred thousand tons of hydrogen could nevertheless convert to helium each second, providing enough energy to power the sun at its current luminosity for about 10 billion years.

  For this important theoretical discovery, Bethe was awarded the Nobel Prize in Physics in 1969, four years after Feynman would share the prize for his own work on quantum electrodynamics (QED). And the nuclear “fusion” reactions Bethe exploited in his explanation of the workings of the sun would be re-created seven years after the end of World War II, in the development of “thermonuclear explosives,” otherwise known as hydrogen bombs.

  Oppenheimer had recruited Bethe in 1942 and wisely chose him to head the Theoretical Division, which contained the biggest brains and the biggest egos that would reside at Los Alamos. Not only was Bethe their intellectual equal, but also his calm yet persistent strength of character would be essential in helping to guide them, put out fires, and, above all, put up with their idiosyncrasies.

  In Feynman, Bethe had found just the foil he needed to bounce ideas off of, just as Feynman had found the perfect mentor to help steer his active imagination. That they both loved their work didn’t hurt either. Bethe, to his credit, recognized Feynman’s talent quickly and made what might seem the unorthodox decision to name the twenty-four-year-old a group leader in the Theoretical Division, outranking colleagues older and more experienced. Stephane Groueff recalled their interactions: “Richard Feynman’s voice could be heard from the far end of the corridor: ‘No, no, you’re crazy!’ His colleagues in the Los Alamos Theoretical Division looked up from their computers and exchanged knowing smiles. ‘There they go again!’ one said. ‘The Battleship and the Mosquito Boat!’ ”

  It is not hard to guess who was who. Nevertheless, beyond the hearty joint laughter and intellectual jousting, what left the most lasting impression on this still impressionable young man was Bethe’s insisting on connecting every theoretical calculation with a number, a quantity that could be compared with experimental results. It is hard to overemphasize how deeply this governed almost everything Feynman did in later life as a scientist. As he later put it, “Bethe had a characteristic which I learned, which is to calculate numbers. If you have a problem, the real test of everything—you can’t leave [it] alone—you’ve got to get the numbers out; if you don’t get down to earth with it, it really isn’t much. So his perpetual attitude is to use the theory. To see how it really works is to really use it.”

  The catalogue of the activities Feynman accomplished while working under Bethe at Los Alamos was remarkable, not least for their diversity. He began by quickly developing a method to numerically integrate (or sum) so-called third-order differential equations, which had derivatives of derivatives of derivatives in them. His method turned out to be more accurate than what one could do with simpler second-order equations. Less than a month later, Feynman and Bethe had worked out their formula for calculating the efficiency of a nuclear weapon.

  He then moved on to the more theoretically challenging problem of calculating the diffusion of fast neutrons that triggered fissions in the uranium 235 atomic bomb. For this problem he developed an approach that was very similar mathematically to the formulation he would eventually create for dealing with QED.

  During the final phases of building the bomb, Feynman was put in charge of computing, ultimately supervising all computational aspects of assembling a successful plutonium bomb, which John von Neumann had suggested could be triggered by a massive implosion, increasing the density of material and making an otherwise stable mass go critical. The first human-induced nuclear explosion, above the desert floor just before sunrise on July 16, 1945, code-named Trinity, was successful in no small part because of Feynman’s calculational leadership in these crucial last months.

  Feynman’s work involved using and even assembling a new generation of electromechanical computing machines to perform the complex modeling calculations necessary to design the new device, which challenged Feynman’s mechanical as well as his mathematical prowess. As Bethe later described it,

  Feynman could do anything, anything at all. At one time, the most important group in our division was concerned with calculating machines. . . . The two men I had put in charge of these computers just played with them, and they never gave us the answers we wanted. . . . I asked Feynman to take over. As soon as he got in there, we got answers every week—lots of them, and very accurate. He always knew what was needed, and he always knew what had to be done to get it. . . . (I should mention that the computer had arrived in boxes—about ten boxes for each. Feynman and one of the former group leaders put the machines together. . . . Later we got some professionals from IBM who said, “This has never been done before. I have never seen laymen put together one of these machines, and it’s perfect!”

  The degree to which Feynman contributed to the successful development of the bomb as he exploited his natural talents and matured as a physicist was well described by the physicist and historian of science Sylvan Schweber: “His versatility was legendary. His genius at lockpicking, repairing Marchant and Monroe calculators, assembling IBM machines, solving puzzles and difficult physics problems, suggesting novel calculational approaches, and explaining theory to experimenters and experiments to theoreticians earned him the admiration of all those with whom he came in contact.”

  Feynman’s talents and energies at Los Alamos derive from a characteristic his old college chum Ted Welton, who later came to Los Alamos to work with him, described: “Once presented with a clearly formulated physical paradox, mathematical result, card trick, or whatever [Feynman] would not sleep until he had the solution.” Schweber agreed, saying this comment captured the quintessential Feynman, who had “an obsessive need to ‘undo’ what is ‘secret.’ ”

  Feynman’s accomplishments were all the more impressive considering that in the midst of all this, his wife lay dying in the Albuquerque hospital. Every week, he made the 200-mile round-trip to visit her, either borrowing cars or hitchhiking all th
e way. His correspondence with her increased as her symptoms worsened, becoming almost daily near the end. Their mutual love, and the tenderness and concern he expressed for her are obvious, and painful to read.

  In the four months before Arline died, on June 16, 1945—six weeks before the first atomic bomb was dropped over Hiroshima—Richard Feynman wrote Arline thirty-two letters. He wrote to doctors to explore and solicit new treatments for tuberculosis, and moved her to the Los Alamos site so they could be closer together, until her unhappiness with the army nurses, the regulations, and the living arrangements caused Richard to move her back to Albuquerque, in spite of his own misgivings. He wrote to her about his regrets about getting drunk on VE Day, about their joint fear that she might be pregnant, about packages from home, about fighting a forest fire, and about men being banned from the girls’ dorm (he joked that he hadn’t been in a girls’ dorm for over a year), but most of all he wrote about his love for her. The very last letter he wrote to her, on June 6, ended as follows:

  I will come this week and if you don’t want to bother to see me just tell the nurse. I will understand darling, I will. I will understand everything because I know now that you are too sick to explain anything. I need no explanations. I love you, I adore you, I shall serve you without question, but with understanding. . . . I adore a great and patient woman. Forgive me for my slowness to understand. I am your husband. I love you.