19 July, 2002 The Editors
Bulletin of the Atomic Scientists 6042 South Kimbark
Chicago ILL 60637 USA
Dear Linda Rothstein, dear Bret Lortie, dear Mike Moore,
Having worked under Werner Heisenberg at his institute for 20 years (1950-1970) and having discussed with him, in 1969, his 1941 visit to Niels Bohr (I recorded immediately afterwards what Heisenberg had told me), it was with great interest that I read the article “The Bohr Letters. No more uncertainty” by William Sweet in the May/June 2002 issue of the Bulletin of the Atomic Scientists. It came to my attention only now.
William Sweet certainly tries to present a balanced analysis of the available material, comparing Bohr’s unsent letters to Heisenberg with the available testimonies by Heisenberg and von Weizsäcker on what was intended with Heisenberg’s visit to Bohr in 1941, and what actually happened, or went wrong, when the visit took place. Unfortunately, W. Sweet is only partially successful. As so many writers before him he is misled by Robert Jungk’s exaggerated interpretation of his interviews with Heisenberg and von Weizsäcker before writing his book “Brighter than a thousand suns” and by Jungk’s selective reproduction of Heisenberg’s critical letters to him. Heisenberg wrote more than 8 pages of which Jungk reproduced only a small part in the English and Danish editions of his book. If all the evidence is taken together it turns out that Bohr’s letters and Heisenberg’s and Weizsäcker’s description of the famous meeting are not incompatible at all. They are complementary.
Heisenberg had known right after the meeting (which was abruptly ended by Bohr) that Bohr had completely misunderstood him. This is now confirmed. Bohr had thought that Heisenberg was trying to get him somehow involved in a German atomic bomb project. Heisenberg had been given no chance to correct Bohr’s erroneous impression. Heisenberg’s letter to Jungk, a fraction of which only is quoted by W. Sweet, goes on to explain how Heisenberg tried to correct Bohr’s misunderstanding and how he did not succeed to regain Bohr’s trust completely, particularly as Heisenberg only dared to speak by way of allusions (which was a mistake, Heisenberg says) out of fear later to be pinned down on what he had said, had the German secret police overheard or found out about their conversation. After all, he talked about a secret project to a foreigner, whereby he risked his neck.
Furthermore, in his letter to Jungk Heisenberg says that he has no good conscience in writing down for him what was said because the wording of the individual remarks cannot be correct (after so many years). It would depend on very fine nuances, Heisenberg wrote, if one wanted to describe correctly the real content of the conversation in its psychological shades. This part of Heisenberg’s letter, quoted neither by Jungk nor Sweet, indicates that Heisenberg is aware of the fact that he may not be able at the time of writing to keep apart what he had carefully prepared to tell Bohr and what was left unsaid because of Bohr’s ending the conversation.
Heisenberg’s intention had been to tell Bohr, in very cautious hints, that atomic bombs were technically possible in principle but extremely difficult to make. Heisenberg did not go into technical details but by September 1941 he knew that both U235 (available from natural Uranium by a very difficult separation process) and what was later called Plutonium (potentially available in sufficient quantity by a very long operation of very large reactors) could be used as explosives. Heisenberg saw indeed, at least in principle, “an open road to the
bomb” but both potential ways of bomb production did not seem technically feasible for many years to come.
Heisenberg did not tell Bohr that the war “would be decided with atomic weapons”. What he probably said was something like “If the war drags on long enough it might be decided by atomic weapons”. That was another way of saying that, in the long run, atomic weapons are possible. But this long time span might provide an opportunity for physicists to come to an international agreement not to work on these bombs. This was the question on which Heisenberg had hoped to get Bohr’s opinion.
The tragical fact is that Bohr misunderstood. The atmosphere for understanding was not favorable. Bohr had been disturbed by Heisenberg’s participation in an astrophysics conference organized by the German Culture Institute in Copenhagen, a progaganda organisation of the Cultural Division of the German Foreign Ministry, which was boycotted by Bohr. For Heisenberg, however, this was the only way by which he could obtain permission to travel to occupied Denmark. Moreover, Bohr had resented remarks by Heisenberg and von Weizsäcker to some members of Bohr’s institute that Germany was about to win the war. That Germany would finally lose was Heisenberg’s conviction at the beginning of the war in 1939 and, of course, after Stalingrad. But in the autumn of 1941 Heisenberg shared the view of many people, not only in Germany, that Germany seemed to win. The United States was neutral. Most of Europe was occupied. German armies were approaching Moscow. To express regrets about the prospects of German victory when the war situation came up, unavoidably, in lunch conversations at the cafeteria in Bohr’s institute, as William Sweet seems to have expected from Heisenberg, would have been suicidal.
After the Copenhagen visit Heisenberg returned to his work on a nuclear reactor for power production. He never tried to build bombs and did not study technical details relevant for their construction. Thus, he had no reason to “white-wash” his activities after the war. Sweet’s statement that “there is no evidence of (Heisenberg’s) formally recommending to higher authorities in the crucial 1941-42 period that they not proceed with a crash weaponization program” is rather astonishing. Higher German authorities, having learned from Heisenberg about the difficulties of bomb production, insurmountable in the near future, had no intention to launch a crash weaponization program. There was no need not to recommend it. On the contrary, mentioning the possibility of a crash program, if only in the context of not recommending it, might have had the opposite effect.
There was no conspiracy at Farm Hall to explain German failure to develop atomic weapons by moral qualms. Weizsäcker just mused about the reasons why German physicists, in contrast to their American colleagues, had not developed crash programs and had worked on their reactor project in a rather unhurried, academic way, simultaneously following other interests as well, like organizing a series of colloquia on cosmic rays and producing a book on this series (editor: Heisenberg). Heisenberg also wrote a treatise on philosophy during the war. Weizsäcker came up with the tentative suggestion that in the heart of their hearts they had not wanted to build a bomb for Hitler. Otto Hahn immediately replied that he did not believe this explanation, and there is no evidence for a general agreement among the interned physicists to adopt Weizsäcker’s considerations for general consumption. Weizsäcker himself later corrected his assumption by conceding that, in any case, the construction of an atomic bomb in Germany under war conditions would have been impossible. However, he maintained that he and Heisenberg were happy about this impossibility and also that both of them considered Hitler a criminal from the beginning.
2
We are left with the paradox which applied to many non-nazi and anti-nazi Germans, including Heisenberg, during the war: They did not want Hitler do win the war, and at the same time they did not want Germany to lose the war. Their hope somehow was that Germany could avoid defeat and that the Army would finally get rid of Hitler. In hindsight we know that this was an illusion although some generals tried, too late and in vain, on July 20, 1944.
I am indebted to historian Prof. Cathryn Carson (Berkeley) for letting me have the full-length texts of Heisenberg’s two letters to Robert Jungk, and to Dr. Helmut Rechenberg, keeper of the Heisenberg archive, for giving his permission.
Sincerely,
Professor (Emeritus) Dr. Klaus Gottstein
19. September 2002 To: The editor of the Bulletin of the Atomic Scientists
Dear Linda Rothstein,
Thank you very much for sending a copy of the September/October issue of the Bulletin which contains my letter. Thank you also for improving my English. I can agree with most of your editing. I regret, however, that you omitted a few words and brief phrases the inclusion of which would not have made my letter much longer but would have helped the reader to understand better Heisenberg’s situation and attitude during the war and put them into the right perspective. These omitted words are:
1.) “not only in Germany” (in between the words “the widely held view” and the words
“that Germany seemed to be winning” in the paragraph starting with “The tragic fact is” on page 5 of the Bulletin). I may remind you that, e.g., according to the memoirs of Katia Mann, wife of Thomas Mann who was at Princeton at the time and acquainted with Einstein, even Einstein thought that the Germans would easily beat the Russians (as they had done in World War I). In Great Britain, as I recently read, many of the leading politicians at that time were in doubt on which material facts Churchill’s optimism regarding Germany’s defeat was based, with the U.S.A. neutral, after German armies had occupied most of Europe and were now approaching Moscow.
Why shouldn’t Heisenberg have had similar impressions?
2.) “simultaneously following other interests as well, like organizing colloquia on cosmic rays and producing a book on them (editor: Heisenberg). Heisenberg also wrote a treatise on philosophy during the war.” ( after the words “in an unhurried, academic way” in the paragraph starting with “There war no conspiracy” on page 72 of the
3
Bulletin.) These omitted words represent the proof of the “unhurried, academic way”.
Without this proof my statement remains an assertion which can just as well be ignored.
3.) “in the heart of their hearts” (in between the words ”that German scientists” and the words “had not wanted to build a bomb for Hitler” in the same paragraph). These (omitted) words were meant to indicate that, according to von Weizsäcker’s tentative musing, the German scientists had, IN AN MORE OR LESS UNCONSCIOUS WAY, not wanted to build a bomb for Hitler. That might have been the reason why the enthusiasm necessary for bringing a project of such dimensions to success was
missing. Omitting these words leaves the reader wondering why the German scientists worked on the project if they did not want it to succeed. In fact, some of the younger scientists, no doubt, wanted to build the bomb, at least consciously, and only some of the leaders, like Heisenberg and von Weizsäcker, realized that this was not feasible, and were happy about it, perhaps also “in the heart of their hearts”.
4.) “although some generals tried, too late and in vain, on July 20, 1944” (after the words
”In hindsight we know that this was an illusion” at the very end of the letter, on page 72.) The omitted words indicate that, although in hindsight we know the outcome, there was indeed opposition to Hitler in the army. This had been known for some time to Heisenberg and others in touch with army circles. Thus, the hope that the army would finally get rid of Hitler was not completely unfounded. Omitting this
explanation can create the impression that hoping for army opposition to Hitler was completely illusionary which it was not.
I felt I should let you know why I think the omissions mentioned above are unfortunate although I realize that it is now too late.
Best regards, Klaus Gottstein
4
