Heisenberg claimed, in his letter to Jungk, that he opened the discussion by asking Bohr whether he believed it was right in time of war for physicists to devote themselves "to the uranium problem—as there was the possibility that progress in this sphere could lead to grave consequences in the technique of war." Heisenberg realized from Bohr's "slightly frightened reaction" that he had immediately understood what Heisenberg meant. As Heisenberg recalled, the Dane responded by asking, "Do you really think that uranium fission could be utilized for the construction of weapons?" According to Heisenberg, he "may have replied: 'I know that this is in principle possible, but it would require a terrific technical effort, which, one can only hope, cannot be realized in this war.'" Bohr was "shocked," assuming that Heisenberg had "intended to convey to him that Germany had made great progress" toward atomic weapons. Heisenberg tried to correct this false impression but could not.
In his later memoirs Heisenberg dealt more briefly with the Copenhagen meeting, but the same leitmotifs appear: his attempt to raise the moral dimension with Bohr, his admission that atomic weapons were possible but only with "a tremendous technological effort," and his insistence that scientists were in a pivotal position, able to "advise their governments that atom bombs would come too late for use in the present war, and that work on them therefore detracted from the war effort, or else contend that, with the utmost exertions, it might just be possible to bring them into the conflict." Once again, he claimed Bohr was too shocked to take in what he was saying. Heisenberg left Copenhagen knowing that his mission had failed. He blamed himself for having spoken too guardedly because he was afraid for his life. Had he had been more explicit, Bohr would have understood him. Bohr's picture of Heisenberg's visit—which his wife, Margrethe, later unequivocally described as "hostile"—was quite different. He was immediately struck by something peculiar in Heisenberg's demeanor, and their meeting deteriorated rapidly. Bohr's earliest account is reported in a letter written in 1946 by the American physicist Rudolf Ladenburg, who repeated Bohr's comments that Heisenberg had expressed the "hope and belief" that if the war lasted long enough, atomic weapons would give Germany victory.
Nearly a decade later, when Bohr read Heisenberg's account of events, reproduced in Robert Jungk's book, he was shocked and angered. In a recently released letter to Heisenberg, drafted but never sent and discovered tucked into Bohr's copy of Jungk's book after Bohr's death in 1962, Bohr wrote, "I am greatly amazed to see how much your memory has deceived you." He taxed Heisenberg with expressing the "definite conviction that Germany would win" and that it was "therefore quite foolish for us to maintain the hope of a different outcome of the war and to be reticent as regards all German offers of cooperation." He also remembered "quite clearly" that Heisenberg spoke in a manner that could only give Bohr "the firm impression" that under his leadership "everything was being done in Germany to develop atomic weapons." Furthermore, Heisenberg had said that "there was no need to talk about details [of atomic weapons]" since Heisenberg was "completely familiar with them and had spent the past two years working more or less exclusively" on them.
Bohr also refuted Heisenberg's suggestion that the news that atom bombs were possible had stunned him into silence, insisting that the possibility of nuclear weapons had been "obvious" to him for a while. The reason he had not spoken was twofold. First, a "great matter for mankind was at issue in which, despite our personal friendship, we had to be regarded as representative of two sides engaged in mortal combat." Second, he was dismayed to learn "that Germany was participating vigorously in a race to be the first with atomic weapons."
Further unsent letters written in subsequent years reveal a softening of Bohr's attitude toward Heisenberg—some affection still remained. A draft letter to Heisenberg congratulating him on his sixtieth birthday ended with "fondest greetings and warmest wishes for many happy years." However, Bohr continued to agonize over Heisenberg's motives. He asked Heisenberg to clarify on whose authority he had come to Copenhagen, writing, "I have often wondered from which official police agency permission was given to talk to me about a question which was surrounded by such great secrecy and held such great dangers." He wanted Heisenberg to tell him "what purpose lay behind" his visit. It was "quite incomprehensible" to him how Heisenberg could claim to have suggested to Bohr "that German physicists would do all they could" to prevent an atomic bomb. On the contrary, "you [Heisenberg] informed me that it was your conviction that the war, if it lasted sufficiently long, would be decided with atomic weapons and I did not sense even the slightest hint that you and your friends were making efforts in another direction."
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Over the years many suggestions have been made about Heisenberg's true purpose. Some have claimed that Heisenberg was trying to discover what Bohr knew about the Allied program. Bohr later told Oppenheimer that Heisenberg and von Weizsacker had come "less to tell what they knew than to see if Bohr knew anything that they did not." It certainly appears that, during his visit to Copenhagen in March 1941, von Weizsacker had been fishing for information. He reported to the Nazi authorities on his return that "concerning the more technical questions," Bohr "knew a great deal less than we."
Others have suggested that Heisenberg was trying to pass messages about the German program to the Allies. According to von Weizsacker, this was true. In a letter in 2002, he wrote, "We hoped that Bohr could tell colleagues in England and the USA that we were no longer working on a bomb." Elizabeth Heisenberg, in her book Inner Exile about life with her husband, similarly suggested that Heisenberg "saw himself confronted with the spectre of the atomic bomb, and he wanted to signal to Bohr that Germany neither would nor could build a bomb. That was his central motive. He hoped that the Americans, if Bohr could tell them this, would perhaps abandon their own incredibly expensive development. Yes, secretly he even hoped his message could prevent the use of an atomic bomb on Germany one day. He was constantly tortured by this idea."
A particularly intriguing dimension is the story that at their meeting Heisenberg gave Bohr a drawing, which, later in the war after his escape from Denmark, Bohr sent to the United States. Robert Oppenheimer, Edward Teller, and Hans Bethe puzzled over the sketch, which showed a boxlike structure with sticklike objects projecting from the top. Bethe recalled, "As far as we could see, the drawing represented a nuclear power reactor with control rods. But we had the preconceived notion that it was supposed to represent an atom bomb. So we wondered: 'are the Germans crazy? Do they want to drop a nuclear reactor on London?'" After further study he and Teller concluded that it "was clearly a drawing of a reactor." Some have claimed that Heisenberg gave the sketch to Bohr as proof that the Germans were working on peaceful, not military, applications of nuclear power. However, Aage Bohr, in whom his father confided, always maintained that Heisenberg gave Bohr no such thing. If the drawing was indeed of German origin, it must have been provided by someone else, although the risks would have been enormous. Otherwise, it may have represented Bohr's own interpretation of German thinking based on his discussions with Heisenberg and others. To heighten the mystery, despite extensive searches in the archives in Denmark, the United States, and the United Kingdom, no trace of the sketch can now be found.
According to Hans Bethe, the Copenhagen meeting was doomed to fail: "It was impossible that the two of them could understand each other. Heisenberg knew about plutonium and was convinced it was the key to the whole business. Bohr didn't know about plutonium. Therefore there was a technical misunderstanding." In Bethe's view, practical considerations also intervened; "Bohr was much better at speaking than listening and he mumbled."
No one will ever know the full truth of what happened and why. Perhaps Heisenberg himself did not know exactly what he was trying to achieve. Perhaps he felt intuitively that to talk to his father figure, Bohr, could clear his mind as it had previously on scientific questions. An English officer after the war recorded private conversations between Heisenberg and von Weizsacker and reported tha
t "they seem to consider international physics as being almost synonymous with work under the leadership of Niels Bohr." Aage Bohr suggested that, as well as respect for his father, affection also played a role: "Undoubtedly one of the reasons why Heisenberg went to Copenhagen was to see if there was anything he could do for his Danish physicist friends living as they were in an occupied country. Heisenberg had a strong sense of loyalty towards them."
However, Heisenberg certainly did not appreciate the sensitivities of the situation. Although eager in his memoirs to portray his readiness to put himself in others' shoes, he was not good at it in reality. He could not place himself in Bohr's position as a half-Jewish citizen of a country occupied by a brutal regime standing for everything Bohr despised. He also had an ability to ignore unpleasant truths and unconsciously to twist them into a more palatable form.
According to Hans Bethe's account of a postwar discussion with Heisenberg, the latter believed passionately that Germany should win the war: "He said he knew that the Germans had committed terrible atrocities against the populations on the Eastern Front—in Poland and Russia—and to some extent in the west as well. He concluded that the Allies would never forgive this and would destroy Germany as a nation—that they would treat Germany about the way the Romans had treated Carthage. This, he said to himself, should not happen; therefore, Germany should win the war, and then the good Germans would take care of the Nazis." Bethe found it "unbelievable that a man who has made some of the greatest contributions to modern physics should have been that naive."
Heisenberg's reasons for visiting Copenhagen were undoubtedly complex, quite possibly confused, and quite likely a combination of the various motives alleged. He may have convinced himself that building an atom bomb before the war was likely to end was currently beyond the capability of any country. However, to protect the Germany he still loved, he had to be sure that Britain and the United States were not making faster progress. Until he knew whether Germany was at risk, he could not decide how he, and his fellow scientists, should act.
Whatever his motives, Heisenberg clearly never got the chance to say all he wanted because Bohr became so agitated. All he achieved was convincing Bohr that Germany was actively pursuing the atomic bomb.
Suspicion about Heisenberg's visit spread quickly. Lise Meitner was alarmed to learn of it from the young Danish physicist Christian Moller when he visited Stockholm several months later. He reported Heisenberg to be "entirely filled with the wish-dream of a German victory." Meitner wrote hastily to Max von Laue in Berlin, who, unknown to his colleagues, had been corresponding regularly with her. They took the precaution of numbering their letters so that they would know whether any had been intercepted. Like Fritz Strassmann, risking his life and that of his family to save the Wolffenstein sisters, von Laue stayed true to his principles, visiting the elderly and lonely Jewish former editor of the scientific journal Naturwissenschaften, Arnold Berliner, marooned in his apartment by fears of anti-Semitic violence until his imminent deportation induced him to commit suicide. Meitner warned von Laue, in guarded, elliptical language, to be wary of Heisenberg and von Weizsacker. She conveyed that she had once thought very highly of the two but added grimly, "It was a mistake."
Von Laue was not particularly surprised by Meitner's warning, replying to her with remarkable perception, "I have often wondered about the inner attitude of Werner and Carl Friedrich, but I believe I understand their psychology. Many people, especially young ones, cannot reconcile themselves with the great irrationality of the present, and so in their imagination they construct castles in the air. It is an enormous task they have undertaken, to find a good side in things they can do nothing about." Heisenberg and von Weizsacker were not, he added, alone in this.
THIRTEEN
"WE'LL WIPE THE JAPS
OUT OF THE MAPS"
FRANKLIN ROOSEVELT'S OFFER to Britain in October 1941 of a partnership received a lukewarm reception. Churchill's preference, like that of his chiefs of staff and some scientists, including James Chadwick, was that any nuclear bomb should be developed in Britain. Not only did Churchill wish to keep control, but he mistrusted American security. In fact, the desire for secrecy was guiding much British thinking. The research director of Imperial Chemical Industries, Wallace Akers, had recently been appointed to head work on both civil and military uses of nuclear energy. He and officials racked their brains for a name for his new organization that had "a specious air of probability about it" while concealing its true purpose. They came up with the plausible-sounding "Directorate of Tube Alloys."
Churchill allowed two months to elapse before replying to Roosevelt's letter. He wrote blandly, "I need not assure you of our readiness to collaborate with the United States Administration in this matter." He told the president that he had arranged for the U.S. scientific liaison officer in London, Mr. Hovde, to have full discussions with Sir John Anderson, the government minister responsible for the Tube Alloys Project, and Churchill's adviser the recently ennobled Frederick Lindemann, now Lord Cherwell. When they met in November 1941, Anderson, an able man but so haughty and inflexible in manner that he was nicknamed "God's butler," coolly informed Hovde that while the British were anxious to collaborate, they were "disturbed about the possibility of leakage of information to the enemy" through the officially neutral United States. Britain wanted strict assurances that the American project would be run in such a way as to preserve maximum secrecy. Unsurprisingly, given Anderson's approach, instead of agreeing on a joint project, the meeting ended with a simple agreement to share some information and with condescending British offers to help "improve" the American organization.
As Britain would soon discover, collaboration restricted to an exchange of information would not be enough to keep it in the race. Ironically, the brilliant Maud Report had provided the impetus for an American program that would soon surge ahead with increasingly little need of, or desire for, British assistance. The French scientist Bertrand Goldschmidt, observing from the sidelines, later wrote that "in this ballet of Anglo-American nuclear relations, the Americans Bush and Conant revealed themselves to be by far the best and most perspicacious advisers." By contrast British officials, in his view "imbued with the antiquated dogma of imperial superiority," missed the boat.
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By late October i 941 the National Academy of Sciences submitted its new report, which, Conant wrote approvingly, "radiated a more martial spirit than the first two." It concluded that a fission bomb "of superlative destructive power" was possible. Based on calculations by Enrico Fermi at Columbia, it estimated that the amount of U-235 required to achieve this could "hardly be less than 2 kg nor greater than 100 kg." It predicted a somewhat lower destructive force than had the Maud Committee but that the loss of life from the effects of radioactivity might "be as important as those of the explosion itself." Furthermore, fission bombs might be achievable "in significant quantity within three or four years" at a cost of between $80 million and $130 million. It defined the priority tasks, in particular assessing the different techniques for separating isotopes of uranium and understanding the engineering requirements of separation plants. Like the Maud Report, it did not mention plutonium. Exactly as German scientists had told the German army, the report warned that in years to come, military superiority would depend on who had nuclear bombs and that "adequate care for our national defense seems to demand urgent development of this program." On 27 November Bush handed the report to President Roosevelt.
In Russia Hitler's exhausted troops were making one last attempt to capture Moscow before winter closed in, inevitably prolonging the war in the East. On Friday 5 December 1941, three feet of snow fell. Nevertheless, eighty-eight new Russian divisions attacked on a five-hundred-mile front and broke through for eleven miles in places before the Germans could stabilize their lines. The next day, 6 December, Hitler was forced to accept that Moscow would not fall quicklv.
On that same Saturday, Vannevar Bush told members of the Uran
ium Committee, gathered in Washington, how he had allocated tasks within the expanded program sanctioned by Roosevelt—known as the "S-1 Project." He appointed three program chiefs, all Nobel Prize winners: Ernest Lawrence was to explore electromagnetic techniques for separating U-23c at Berkeley and to supply the first samples of enriched uranium for experiments; Harold Urey, the discoverer of deuterium, was to develop gaseous diffusion separation methods, as advocated by the Maud Committee, at Columbia University; Arthur Compton, the pioneer of gamma ray research, was responsible for theoretical studies and bomb design at the University of Chicago, where he himself was based, and elsewhere. In addition, the industrialist Eger. Mur-phree, Standard Oil of New Jersey's research director, was to oversee the development of high-speed centrifuge technology for separating U-235. and to take responsibility for broad engineering issues such as procuring materials and constructing pilot and production plants.
Lawrence had become an increasingly strong proponent of electromagnetic separation as the simplest route for U-235. production. The process used magnetic force in a device called a mass spectrograph to bend beams of charged uranium particles into circular paths. The precise path of each particle was determined bv its mass. Therefore, the heavier isotope U-238, with its greater mass, took a different path than the lighter U-235, making it possible to collect the two in separate containers. Lawrence ordered his team to convert Berkeley's thirty-seven-inch cyclotron into a mass spectrograph. On the very morning that Bush was assigning work to his top scientists, news came that the Berkeley spectrograph had started work. It was producing a microgram of U-235. an hour—not much, but a start.
Before the Fallout Page 23