Abstract
Sweating it out
As a retired noncommissioned officer I find your magazine essential for understanding what is going on in the world today. I am actually more concerned about the potential for nuclear disaster now than at any other time in my life.
It is incomprehensible that seniorlevel government officials are talking about preemptive strikes and low-yield nuclear weapons. The rhetoric and arrogance remind me of those heady days when, while sitting on an Atlas E (CGM-16E) missile site in Kansas, beads of sweat would gather on my forehead every time the primary alert system activated. America must reject the notion that a nuclear weapon, either by threat or by use, can achieve any level of peace. Your magazine and its clock are sending a message that should be understood by all who live in our country.
Halifax, Pennsylvania
William Sweet's article, “The Bohr Letters: No More Uncertainty” (May/June 2002 Bulletin), unfortunately contains two mistakes:
First, it wasn't Peter Jensen who visited Bohr in Copenhagen during the war, but Johannes Jensen. Peter Jensen was an assistant to Walther Bothe and worked in Heidelberg on the absorption cross sections of neutrons. Johannes Jensen was an assistant professor of theoretical physics in Hamburg. Part of the reason he visited Copenhagen was because he had relatives in Scandinavia.
Second, the only experiment Johannes Jensen and Paul Harteck worked on together took place in Hamburg in June 1940 and was of a completely different design than the one in Bohr's diagram.
Johannesburg, South Africa
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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, it was with great interest that I read William Sweet's article, “The Bohr Letters: No More Uncertainty.”
Sweet tries to present a balanced analysis of the available material on Heisenberg's visit—comparing Bohr's unsent letters to testimonies from Heisenberg and Carl von Weizsäcker about Heisenberg's intent—but he is only partially successful. Like many writers before him, Sweet is misled by Robert Jungk's exaggerated interpretation of his interviews with Heisenberg and von Weizsäcker, and by Jungk's selective reproduction of Heisenberg's critical letters to him. Heisenberg wrote more than eight pages, of which Jungk reproduced only a small part in the English and Danish editions of his book, Brighter Than a Thousand Suns.
When all the evidence is taken into account, Bohr's letters and Heisen-berg's and von Weizsäcker's descriptions of the famous meeting are not incompatible. They are complementary. Heisenberg realized right after the meeting (which was abruptly ended by Bohr) that Bohr had completely misunderstood him. This is now confirmed. Bohr thought that Heisenberg was trying to involve him in a German atomic bomb project. But Heisenberg was not given the chance to correct this erroneous impression.
In his letter to Jungk, only a fraction of which is quoted by Sweet, Heisenberg explains how he failed to correct Bohr's misunderstanding, particularly because he spoke only by allusions (which, Heisenberg admitted, was a mistake). He feared that if the German secret police overheard or found out about the conversation they would pin him down about what he had said. He was, after all, talking with a foreigner about a secret German project.
Heisenberg also told Jungk that he could not in good conscience write down all that was said at the meeting because after so many years he would not be able to recall precisely the individual remarks, which were extremely nuanced. Heisenberg's intention had been to tell Bohr, in very cautious hints, that although in principle it was possible to make atomic bombs, it would be very difficult. Heisenberg did not go into technical details, but by September 1941 he knew that both uranium 235 and another as yet unnamed element (plutonium) could be used as explosives. Although Heisenberg saw “an open road to the bomb,” he thought that it would not be technically feasible to produce it for many years.
Mordechai Vanunu's letter to the Bulletin was heavily edited by the censors at Ashkelon prison, Israel.
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,” which was another way of saying that, in the long run, atomic weapons were possible. Heisenberg realized, however, that this long time span could provide physicists the opportunity to come to an international agreement not to work on the weapons. It was on this issue that Heisenberg had hoped to get Bohr's opinion.
The tragic fact is that Bohr misunderstood. The atmosphere was not favorable for understanding. Bohr was disturbed by Heisenberg's participation in an astrophysics conference organized by the German Culture Institute in Copenhagen, a German Foreign Ministry propaganda organization, which Bohr boycotted. Heisenberg, on the other hand, saw the conference as the only way he could obtain permission to travel to occupied Denmark. Bohr also resented remarks by Heisenberg and von Weizsäcker to members of Bohr's institute that Germany was about to win the war.
That Germany would finally lose was Heisen-berg's conviction at the beginning of the war in 1939 and, of course, after Stalingrad. But in the autumn of 1941 Heisenberg shared the widely held view that Germany seemed to be winning. The United States was neutral; most of Europe was occupied; and German forces were closing in on Moscow. To have expressed regret about a potential German victory—as Sweet suggests Heisenberg should have done—when the subject of the war came up during lunch conversations at the cafeteria in Bohr's institute would have been suicidal.
After the Copenhagen visit, Heisenberg returned to his work on a nuclear power reactor. He never tried to build bombs and did not study the technical details necessary for their construction. Thus, he had no reason to “white wash” his activities after the war. Sweet's statement that “there is no evidence [that Heisenberg] formally recommend[ed] to higher authorities in the crucial 1941–42 period that they not proceed with a crash weaponization program” is rather astonishing. German authorities, having learned from Heisenberg about the difficulties of bomb production, had no intention of launching a crash weaponization program. It was not necessary to recommend against it. On the contrary, the mere mention of the possibility of a crash program, even if only in the context of recommending against one, might have had the opposite effect.
Update
In the January/February 2001 Bulletin, Aluf Benn reported on growing U.S. and Israeli concerns over the transfer of missile and nuclear technology from Russia to Iran, where Moscow has an $800 million contract to build a nuclear reactor. An Israeli official asked Benn, “Why would Iran, one of the world's largest oil producers, need a nuclear power station?”
Now that official might be wondering why Iran needs multiple nuclear power plants. In late July, Russia announced that it has plans to build five other reactors in Iran—three more at Bushehr, and two at Akhvaz.
“It's fair to say the White House was infuriated by that and extremely surprised,” a Bush official told the Washington Post (July 29). The Post also reported that some unnamed defense officials are pushing for the destruction of the plant before it receives any fuel.
Both the United States and Israel worry that Iran could be using the reactor as a cover for a nuclear weapons program. The CIA says Iran is about seven years from having a bomb; Israel says five. (Iran's Shihab-3 has a range of 1,300 kilometers, and Iran is thought to be developing a longer-range missile.) Iran, which is a Nuclear Non-Prolifer-ation Treaty signatory, denies its nuclear program is for anything other than peaceful purposes.
For its part, Russia, perhaps the only country that claims to believe Teheran, has said that it will not allow Iran to reprocess the spent fuel, which will be returned to Russia for storage.
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There was no conspiracy at Farm Hall to explain that Germany failed to develop atomic weapons because of moral qualms. Von Weizsäcker 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 an unhurried, academic way. Although von Weizsäcker tentatively suggested that German scientists had not wanted to build a bomb for Hitler, Otto Hahn immediately replied that he did not believe this explanation. Von Weizsäcker himself later corrected his assumption by conceding that, in any case, the construction of an atomic bomb in Germany under war-time conditions would have been impossible. However, he stood by his story that he and Heisenberg were happy about this impossibility and that both of them considered Hitler a criminal from the beginning.
We are left with the paradox that plagued many non-Nazi and antiNazi Germans, including Heisenberg, during the war: Although they did not want Hitler to win the war, they did not want Germany to lose. Their hope was that Germany could somehow avoid defeat and that the army would finally get rid of Hitler. In hindsight we know that this was an illusion.
Max-Planck-Institut für Physik, Munich, Germany
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Michael Schaaf is correct, I con-fused Hans Jensen with Peter Jensen. I apologize for the mistake. Jeremy Bernstein argues it was Hans (not Peter) who brought a German reactor diagram to Bohr. Bernstein's key point, which I regret obscuring, is that the reactor design described in the diagram did not yet exist in 1941. Therefore, Bohr must have gotten the drawing, or at least the idea, from someone else. Bernstein stands by his statement that it was Hans Jensen who told Bohr about the reactor design, which he would have known about because of related work he was doing with Harteck.
I appreciate Klaus Gottstein's careful and reasonable comments. I'd like to emphasize, however, that while I do not attach great importance to any of the Jungk material as such, I cannot agree that Heisenberg's and Bohr's accounts of the Copenhagen meeting are complementary. They are radically different, especially with regard to the moral issues that are of decisive importance, including Heisenberg's evident inability to understand Bohr's rage over his satisfaction with the progress of Germany's war effort; his associating himself with that effort; and his inability to understand the profound dubiousness of working to develop a technology that could end up giving an atomic bomb to Hitler.
These same issues are decisive in evaluating the issue of a crash weap-onization program. As historian Mark Walker has spelled out, several months after the Copenhagen meeting the German scientists were informed by the leadership that continuation of the nuclear program could be justified “only if military applications of nuclear fission could be expected in the foreseeable future” (Walker's words). Army Ordnance submitted a report to the leadership, based on input from Heisenberg and others, in which it was recommended they “take the considerable and consequential step from laboratory to industrial-scale research and development.” It is true that Heisenberg—mindful of his position as a top science policy adviser and wishing to provide strictly objective counsel—did not oversell the prospects of developing a bomb in time to influence the outcome of the war. But in a number of reports to the top leadership, Heisenberg made clear that successful development of a reactor would provide the means of making fissionable material for a bomb—the “open road” to the bomb the German scientists had discovered during the summer before the Copenhagen visit, and which was the main impulse for the visit.
Regarding my discussion of Farm Hall, I hope that it is not misread as implying that all scientists in detention in England equally conspired in developing the Farm Hall alibi. On the contrary, von Weizsäcker played the main role, with Heisenberg acting as friendly critic and editor. Max von Laue was entirely hostile to the project and later dubbed it the “Farm Hall Lesart” in a letter to Paul Rosbaud, which Arnold Kram-ish first publicized in his book, The Griffin.
As to Heisenberg's attitude toward the war, I am grateful for Gottstein's admirable formulation—that Heisenberg did not want Hitler to win and did not want Germany to lose. It was precisely this attitude, in conjunction with his mention of the bomb possibility at Copenhagen, that made Bohr go ballistic.