Significantly, Bush associated the reservation of policy with relief from criticism: “Much of the difficulty in the past has been due to the fact that Ernest Lawrence in particular had strong ideas in regard to policy, and talked about them generally. . . . I cannot. . . . bring him into the discussions, as I am not authorized by the President to do so.” He applied just this test—silence on policy—to measure Lawrence’s and Compton’s loyalty: “I think [Lawrence] now understands this, and I am sure that Arthur Compton does, and I think our difficulties in this regard are over.”
A scientist could choose to help or not to help build nuclear weapons. That was his only choice. The surrender of any further authority in the matter was the price of admission to what would grow to be a separate, secret state with separate sovereignty linked to the public state through the person and by the sole authority of the President.
Patriotism contributed to many decisions, but a deeper motive among the physicists, by the measure of their statements, was fear—fear of German triumph, fear of a thousand-year Reich made invulnerable with atomic bombs. And deeper even than fear was fatalism. The bomb was latent in nature as a genome is latent in flesh. Any nation might learn to command its expression. The race was therefore not merely against Germany. As Roosevelt apparently sensed, the race was against time.
There are indications in Bush’s memorandum that Roosevelt was concerned less with a German challenge than with the long-term consequences of acquiring so decisive a new class of destructive instruments. “We discussed at some length after-war control,” Bush wrote Conant, “together with sources of raw material” (sources of raw material were then believed to be few and far between; whoever commanded them might well, it seemed, monopolize the bomb). Roosevelt was thinking beyond developing bombs for the war that the United States had not yet entered. He was thinking about a military development that would change the political organization of the world.
Bush, who was a successful administrator partly because he knew the limits of his charter, then suggested that a “broader program”—industrial production—ought to be handled when the time came by some larger organization than the OSRD. Roosevelt agreed. Summarizing his assignment, Bush told the President he understood he was to expedite in every possible way the necessary research but was “not [to] proceed with any definite steps on this expanded plan until further instructions from him. . . . He indicated that this was correct.” The money, the President told him, “would have to come from a special source available for such an unusual purpose and . . . he could arrange this.”
The United States was not yet committed to building an atomic bomb. But it was committed to exploring thoroughly whether or not an atomic bomb could be built. One man, Franklin Roosevelt, decided that commitment—secretly, without consulting Congress or courts. It seemed to be a military decision and he was Commander in Chief.
* * *
Bush and Conant proceeded to order up from Arthur Compton a third NAS review. Compton asked Samuel Allison for the name of someone who could help him calculate the critical mass of U235. Allison had been corresponding with Enrico Fermi on the subject of carbon absorption cross sections and recommended him highly. Compton “called on Fermi in his office at Columbia University.1482 Stepping to the blackboard he worked out for me, simply and directly, the equation from which could be calculated the critical size of a chain-reacting sphere. He had at his fingertips the most recent experimental values of the constants. He discussed for me the reliability of the data. . . . Even the most conservative estimate showed that the amount of fissionable metal needed to effect a nuclear explosion could hardly be greater than a hundred pounds.”1
Compton moved on to Harold Urey’s office to look into isotope separation. Urey was the recognized world leader in the field as a result of his Nobel Prize-winning work with hydrogen isotopes; he had directed isotope separation studies for the Uranium Committee and the Naval Research Laboratory since the beginning. He personally investigated chemical separation of U235 (which turned out to be impossible given the chemical compounds of the day) and separation by centrifuge. Estimating that a centrifuge plant that would produce one kilogram of U235 per day would require 40,000 to 50,000 yard-long centrifuges and would cost about $100 million, he had recently contracted with Westinghouse in the name of the Uranium Committtee for a prototype unit.
Urey was initially skeptical of gaseous barrier diffusion. He and John Dunning were not compatible, perhaps because they were both enthusiasts, and only when centrifuge development was well under way, in late 1940, did Urey turn his attention to the process that Dunning and Eugene Booth were working hard at their own expense to develop. They had chosen gaseous diffusion at dinner one evening in 1940 on their way home from a trip to Schenectady by systematically ruling out other methods as unsuitable for large-scale production, much as Peierls and Simon had done.1483 They were interested in nuclear power, Booth remembers, not bomb-making. “Our reasons for pursuing the isotope separation path toward power production were simple and general. If a chain reaction became possible with normal uranium, a smaller and probably cheaper power plant could be made with enriched uranium.”1484
Dunning and Urey produced a joint appraisal of the gaseous-diffusion process in November 1940. Dunning’s barrier material at the time was fritted glass—partially fused and therefore porous silica, the material from which porcelain is made—which uranium hexafluoride was likely to corrode.1485 They estimated that a gaseous-diffusion plant would involve some five thousand separate barrier tanks—“stages”—but made no attempt to determine cost and power requirements.
By the autumn of 1941, without official support, Dunning and Booth had nevertheless made significant progress. They had switched to brass barriers from which the zinc had been etched (brass is an alloy of copper and zinc; etching away the zinc made the material porous). In November, the month after Compton’s visit, they would successfully enrich a measurable quantity of uranium with their equipment.
Compton traveled next to Princeton to see Eugene Wigner, who had been working closely with Fermi. Wigner clarified for Compton the difference between fast- and slow-neutron fission. He endorsed the uraniumgraphite system Fermi was developing as a method for producing 94. “He urged me,” writes Compton, “almost in tears, to help get the atomic program rolling. His lively fear that the Nazis would make the bomb first was the more impressive because from his life in Europe he knew them so well.”1487
Back in Chicago Compton talked to Glenn Seaborg, who had come east from Berkeley at Compton’s request. Seaborg was confident he could devise a large-scale, remote-controlled technology for separating 94 chemically from uranium.
Armed with this new round of information Compton called a meeting of his committee for October 21 in Schenectady.1488 He prepared for the meeting by writing a draft report. A letter came from Lawrence saying he wanted to bring along Robert Oppenheimer: “I have a great deal of confidence in Oppie, and I’m anxious to have the benefit of his judgment in our deliberation.”1489 Conant had scolded Lawrence at Compton’s fireside when he learned that Lawrence had asked Oppenheimer, still an outsider, for help with theory, but now Lawrence’s request was granted.1490
A dispute between Lawrence and Oppenheimer about what Lawrence called the theoretician’s “leftwandering activities” almost excluded him from the atomic bomb project.1491 Oppenheimer, married now to the former Katherine Puening, known as Kitty, with a six-month-old son, had begun to wish for assignment. “Many of the men I had known went off to work on radar and other aspects of military research,” he testified later. “I was not without envy of them.”1492 He learned the price of admission when he invited Lawrence to an organizational meeting at his elegant new home on Eagle Hill for a professional union, the American Association of Scientific Workers, of which Arthur Compton, among others, was a senior member. Lawrence wanted no part in any “causes and concerns,” as he called political activities, and barred his staff as well: “I don’t thin
k it’s a good idea,” he told them.1493 “I don’t want you to join it. I know nothing wrong with it, but we’re planning big things in connection with the war effort, and it wouldn’t be right. I want no occasion for somebody in Washington to find fault with us.” Oppenheimer was not so easily put off; he debated Lawrence’s point, arguing that humanity was everyone’s responsibility and that the more fortunate should help “underdogs.” The Nazis came first, Lawrence countered.1494 He told Oppenheimer about Conant’s scolding. Oppenheimer reserved judgment. The October 21 meeting, where he could measure the scientific leaders of the uranium program against his own formidable gifts, changed his mind. “It was not until my first connection with the rudimentary atomic-energy enterprise,” he testifies, “that I began to see any way in which I could be of direct use.”1495 When he saw his way to war work he quickly sacrificed his underdogs, writing Lawrence on November 12:
I . . . assure you that there will be no further difficulties at any time with the A.A.S.W. . . . I doubt very much whether anyone will want to start at this time an organization which could in any way embarrass, divide or interfere with the work we have in hand. I have not yet spoken to everyone involved, but all those to whom I have spoken agree with us: so you can forget it.1496
Lawrence opened the Schenectady meeting by reading Oliphant’s summary of the MAUD Report. Compton followed with a review based on his October travels. Oppenheimer weighed in during the discussion of U235’s critical mass with an estimate of 100 kilograms, 220 pounds, close to Fermi’s estimate of 130,000 grams. “Kistiakowsky,” writes Compton, “explained the great economic advantage of being able to deliver a heavy blow with a bomb carried by a single plane.”1497
But Compton was distressed to discover he could not move the engineers on the review committee—the practical souls Bush had insisted be added to bring the NAS reviews down to earth—to estimate either how much time it would take to build a bomb or how much the enterprise would cost:
With one accord they refused. . . . There weren’t enough data. The fact was that they had before them all the relevant information that existed, and some kind of answer was needed, however rough it might be, for otherwise our recommendation could not be acted upon. After some discussion, I suggested a total time of between three and five years, and a total cost . . . of some hundreds of millions of dollars. None of the committee members objected.
So the American numbers came out of a scientist’s hat, as the British numbers had. Atomic energy was still too new for engineering.
If Compton was distressed by the refusal of commitment, Lawrence was appalled. Within twenty-four hours he mailed the committee chairman a bracing challenge edged with threat:
In our meeting yesterday, there was a tendency to emphasize the uncertainties, and accordingly the possibility that uranium will not be a factor in the war. This to my mind, was very dangerous. . . .1498
It will not be a calamity if, when we get the answers to the uranium problem, they turn out negative from the military point of view, but if the answers are fantastically positive and we fail to get them first, the results for our country may well be tragic disaster. I feel strongly, therefore, that anyone who hesitates on a vigorous, all-out effort on uranium assumes a grave responsibility.
But Compton had already been threatened by an expert, Vannevar Bush, and knew his duty well, though he did not yet know that Bush was already committed to expedition and expansion. He had difficulty estimating “the destructiveness of the bomb.” The calculation “involved problems of gas pressure, specific heats at hitherto unknown temperatures, the transmission of radiations and particles through the material, and forces of inertia.”1499 He asked Gregory Breit for help. Breit was even more obsessed with secrecy than Briggs. “No help was forthcoming,” says Compton, gritting his teeth. He turned then to Oppenheimer. “I had known ‘Oppie’ for some fourteen years and had found him most competent in seeing the essentials of an intricate problem and in interpreting what he saw. So I was glad to get a letter from him with helpful suggestions.”1500 Through the end of October Compton worked on.
* * *
At Leipzig in September Werner Heisenberg received the first forty gallons of heavy water from Norsk Hydro and immediately prepared another chain-reaction experiment like the unsuccessful effort at the Virus House in Dahlem the year before: a thirty-inch aluminum sphere filled with alternating layers of heavy water and uranium oxide, more than three hundred pounds of it, arranged around a central neutron source, the sphere itself then immersed in water in a laboratory tank. This time Heisenberg found some increase in neutrons, enough to extrapolate eventual success. The German laureate knew now from the work of von Weizsácker and Houtermans that a sustained chain reaction in natural uranium would breed element 94. “It was from September 1941,” he remarks in consequence, “that we saw an open road ahead of us, leading to the atomic bomb.”1501
He decided to talk to Bohr. To what end he thought Bohr might help him he never unambiguously explained. His wife Elisabeth believes “he was lonely in Germany. Niels Bohr had become a father figure to him. . . . He thought that he could talk about anything with Bohr. . . . The advice of an older friend, more experienced in human and political affairs, had always been important to him.” He “saw himself confronted with the spectre of the atomic bomb,” Elisabeth Heisenberg explains, “and he wanted to signal to Bohr that Germany neither would nor could build a bomb. . . . Secretly he even hoped that his message could prevent the use of an atomic bomb on Germany one day. He was constantly tortured by this idea. . . . This vague hope was probably the strongest motivation for his trip.”1502
Heisenberg and von Weizsäcker attended a scientific meeting in Copenhagen at the end of October, a meeting Bohr routinely boycotted as he boycotted all joint Danish and German activities, to emphasize his refusal to collaborate. He was willing to see Heisenberg, however, and received him, according to the German physicist’s wife, “with great warmth and hospitality.”1503
Heisenberg saved his crucial conversation for a long evening walk with Bohr through the brewery district around the Carlsberg House of Honor. “Being aware that Bohr was under the surveillance of the German political authorities,” he recalled after the war, “and that his assertions about me would probably be reported to Germany, I tried to conduct this talk in such a way as to preclude putting my life into immediate danger.” Heisenberg remembers asking Bohr if it was right for physicists to work on “the uranium problem” in wartime when there was a possibility that such work could lead to “grave consequences in the technique of war.” Bohr, who had returned from the United States convinced that a bomb was practically impossible, “understood the meaning of the question immediately, as I realized from his slightly frightened reaction.” Heisenberg apparently thought Bohr was privy to American secrets and was reacting guiltily to implicit exposure. But Bohr’s next response suggests that he had been, rather, stunned at Heisenberg’s revelation: he asked Heisenberg if a bomb really was possible. Heisenberg says he answered that a “terrific technical effort” would be necessary, which he hoped could not be realized in the present war. “Bohr was shocked by my reply, obviously assuming that I had intended to convey to him that Germany had made great progress in the direction of manufacturing atomic weapons. Although I tried subsequently to correct this false impression I probably did not succeed. . . . I was very unhappy about the result of this conversation.”1504
Thus Heisenberg’s version of the evening walk. Bohr’s is less detailed. His son Aage, a Nobel laureate in his turn and his father’s successor as director of the Copenhagen institute, summarizes it in a memoir:
The impression that in Germany great military importance was given to [atomic energy research] was strengthened by the visit to Copenhagen in the autumn of 1941 of Werner Heisenberg and C. F. von Weizsäcker. . . . In a private conversation with my father Heisenberg brought up the question of the military applications of atomic energy. My father was very reticent and expressed his
scepticism because of the great technical difficulties that had to be overcome, but he had the impression that Heisenberg thought that the new possibilities could decide the outcome of the war if the war dragged on. . . . [Heisenberg’s] account [of the meeting] has no basis in actual events.1505
Robert Oppenheimer, who also had the story direct from Bohr, condenses the meeting to the comment: “Heisenberg and von Weizsäcker came over from Germany, and so did others. Bohr had the impression that they came less to tell what they knew than to see if Bohr knew anything that they did not; I believe that it was a standoff.”1506
The two accounts are not incompatible, but both leave out a crucial fact: that Heisenberg passed to Bohr a drawing of the experimental heavywater reactor he was working to build.1507 If he did so clandestinely he certainly risked his life. If he did so cynically and with Nazi approval to misdirect Allied intelligence he was certainly no longer attached to Bohr as a father figure, as Elisabeth Heisenberg writes. Whatever his intent, it had the wrong effect on Bohr. Elisabeth Heisenberg thinks “Bohr essentially heard only one single sentence: The Germans knew that atomic bombs could be built. He was deeply shaken by this, and his consternation was so great that he lost track of all else.”1508 But Aage Bohr’s and Oppenheimer’s accounts imply a further response from Bohr: indignation, even incredulity, that Heisenberg would think Bohr might be willing in any way, for any reason, to cooperate with Nazi Germany. Heisenberg, in turn, was aghast that Bohr would fail to see and credit his reservations, would not understand, as his wife writes, that his “bond to his country and its people was not tantamount to a bond to the regime.” To the contrary, she adds, “Bohr told Heisenberg that he understood completely that one had to use all of one’s abilities and energies for one’s country in time of war.” Not surprisingly, since it implied Bohr thought the worst of him—that he was willing to work for the Nazis—“Heisenberg was deeply shocked by Bohr’s reply.”1509