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By Frederick Seitz
The final public release earlier this year of several drafts of a letter that Niels Bohr wrote to Werner Heisenberg in the mid-1950s, but never sent, gives us a somewhat deeper insight into the meeting between the two that took place in Copenhagen in September, 1941. Germany was then at the height of its period of military success, having occupied most of Europe, defeated France, and driven the British Army off the continent. The US was still technically neutral and the destructive bombardment of Pearl Harbor lay several months ahead. Denmark had been forcibly occupied, so Bohr could not help but be apprehensive about the visitors from an enemy country, in spite of what had previously been a deeply friendly professional relationship.
While we do not know full details about their discussions, the record makes it clear that Heisenberg brought up - in what appears to be a heavy-handed way - two issues that were guaranteed to raise Bohr's ire. Since German victory in the war now seemed assured, Heisenberg suggested that Bohr takes steps to promote friendly relations between Denmark and Germany. Bohr could only have been incensed at the proposal. He was a very loyal Dane, a notable distinguished father-figure in his country, and he well knew that his fellow citizens were outraged by the German occupation. The notion that Bohr would support any official form of friendly relationship was simply beyond comprehension under the circumstances. On the more personal side, Bohr was partly Jewish and must have despised the German leadership for promoting the anti-Semitic Nuremberg Laws.
In a similar manner, Heisenberg stated that he and a group of colleagues were in the process of developing a nuclear chain reaction based on the fission of uranium. If we can trust Bohr's memory a decade and a half later, Heisenberg implied that he had a fairly complete understanding of the steps needed to achieve such a reaction, but would not go into details. He also stated that work of this kind would ultimately lead to the development of some form of nuclear bomb that would probably play a crucial role in bringing the war to an end if they succeeded. He could not at that time have realized how fully prescient he was, since the Pacific war was far away and the US was not yet engaged. Clearly such an admission would have angered Bohr at least as much as the proposal that he cooperate with the existing German government.
What are we to make of this, beyond concluding that Heisenberg proved to be a poor diplomat during the visit and, in fact, behaved much like the proverbial bull in a china shop? It is likely that the first proposal to Bohr, suggesting that he take the lead in developing cultural links with German counterparts, was the primary goal of the visit as contrived in the diplomatic offices in Berlin, and was made a condition for permission to visit Denmark. Had Heisenberg possessed more sensitive feelings regarding Bohr's special position as a leading Danish citizen, he would have refused, realizing that it would only pour salt in an open wound and severely damage what had once been a warm, valuable friendship.
Perhaps the key to the situation lies in Heisenberg's personal pride at that moment, both in German military prowess and what he viewed as the significant strides he was making on the road to releasing high levels of nuclear energy. Had Hitler not come to power, and had political and economic affairs in Germany stabilized, Heisenberg's intellectual life would undoubtedly have continued to be centered in physics and the academic world. However, he came from a patriotic family and felt very strongly that he should do his best to preserve what he could from the shambles in his intellectual world created once Hitler came to power. He also felt a patriotic duty as a German citizen to take his place in military service and related matters.
Yet Heisenberg faced many difficult confrontations with German government leaders on matters of socio-ethical policies. A small group of physicists who were highly supportive of Hitler designated him a "White Jew" in the official press of the Nazi Party for giving lectures on Einstein's theory of relativity. This caused the government to carry out an in-depth investigation of his status, making him a marked individual. One wonders if his willingness to cooperate with the government by carrying out "cultural missions" in the occupied countries before and during the war stemmed from the hope that he could regain some degree of credibility with officialdom and exert positive influence on behalf of the scientific community.
He did have opportunities to escape, particularly in the summer of 1939, when he came to the US to lecture at the University of Michigan summer school. There he met his good friend Enrico Fermi, who had just succeeded in emigrating from Italy with his family. Fermi implored him to remain in the US, where he would enjoy a top-flight position, emphasizing that Heisenberg could never accomplish anything significant back in Germany, because those now in charge of the government had no appreciation for his ideals and goals. Heisenberg, in turn, stated that he felt an obligation to try and save something out of the wreckage that was emerging in his country. Moreover, he would have had to leave his family behind, since it would have been impossible to gain permission to take them abroad at that late date. Restrictions on foreign travel had become very tight. Furthermore, he may well have thought that he might be called upon by the US to help develop a nuclear bomb that would threaten his homeland.
Fermi not only had some 15 years of experience living under a dictatorship led by individuals with the same mentality as the Nazi leaders, but had by nature or acquisition developed appropriate "street smarts" that enabled him to understand exactly what was at stake. Heisenberg possessed neither the experience nor the gifts of insight that Fermi did. He was guided by a code, probably closely related to that of his patriotic family, which demanded that he go back and support his country and possibly save some of the residual scientific structure in Germany. The result was a disaster for which he paid a great personal price. He accomplished essentially nothing except perhaps to keep a small group of scientists sufficiently engaged in practical work to remain free of army service, although late in life he devoted much time and effort to science and public policy, particularly with regard to the changing course of the German educational system in the mid 1960s.
Events took a very different turn from that which Heisenberg anticipated in September of 1941. He emerged from the war a very chastened individual. During Heisenberg's visit to Fermi in the US shortly after the end of World War II, a graduate student remarked, "It's hard to believe that guy ever did anything important." Fermi admonished him sharply, saying, "You should have seen him at the peak of his creative period." During the course of a long and distinguished physics career,
Frederick Seitz was President of the APS in 1961, President of the N.ational Academy of Sciences from 1965 to 1968, and President of Rockefeller University from 1968 to 1978.