Quantum Man: Richard Feynman's Life in Science by Lawrence M. Krauss Page B

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