To the Editors:

While taking up the invitation to make a few comments on the extensive articles by Thomas Powers and Michael Frayn published in the March 28, 2002, issue, I can’t suppress the thought that it might have been instructive to balance those pieces with others in the same issue by historians familiar with the matter they discuss.

As to Mr. Powers’s piece, it is his attempt to show that the newly released Niels Bohr documents, despite their explicit contradictions to his thesis (see, essentially “leave the rest pretty much where it was.” The implication throughout is that Mr. Powers’s widely read book, Heisenberg’s War (1993), and his many articles—in which the central theme was always that Heisenberg understood all along what had to be done to build a bomb, but kept it secret from everyone—also remain pretty much valid. Nowhere does Mr. Powers indicate where the new documents and other earlier critiques require any modification, even though, as Michael Frayn himself has remarked in one of his early postscripts, Mr. Powers has not found any historian to credit his basic idea.

Mr. Powers’s defense is not unexpected. He is burdened with his published assessment that “something about Heisenberg’s visit to Copenhagen in 1941 deeply angered …Bohr,” whereas Heisenberg, “in comparison to Bohr…was a fount of candor and detail” [NYR, September 20, 2001]. But some of the details he offers now in the new article might mislead readers. One or two examples here must suffice. Thus he quotes Carl Friedrich von Weizsäcker introducing a new idea, immediately after hearing that the Allies had succeeded in making an atomic bomb: “I believe the reason we didn’t do it was because all the physicists didn’t want to do it, on principle….” But Mr. Powers does not go on to cite the response, immediately following that remark, from Otto Hahn, one of the ten nuclear scientists present: “I don’t believe that”—which nobody there contradicted. Mr. Powers also does not refer to Max von Laue’s exposé that this new formulation was intended as a face-saving device. Nor does he cite Heisenberg’s remark on that same evening, during the discussion of how a bomb might be made, that in the spring 1942 meeting with the minister for research, “we convinced him that we had absolutely definite proof that it could be done.” (For context and explanatory details, see the authoritative book on the subject, Jeremy Bernstein’s Hitler’s Uranium Club: The Secret Recordings at Farm Hall, Copernicus Books, 2001, especially pages 115–140—whose author Mr. Frayn, in Postscript II to his published play Copenhagen, calls “the best informed and most fair-minded.”)

We know from various documents, including the new ones from Bohr, that at least as late as 1941 Heisenberg was not the only German scientist who predicted Germany’s victory, and tried to persuade audiences in other countries to join in the pursuit of that victory. Mr. Powers, however, prefers to concentrate on Heisenberg’s disillusionment with Hitler’s war at its end. That misses an opportunity to help us understand the change. I feel sure that Werner Heisenberg, as shown through his many books and through several pleasant meetings I had with him after the war, was a highly cultured person imbued with German patriotism of the old sort. While, like many Germans, he was willing to give priority to the state regardless of its leadership, he quietly despised the Nazi authorities at least as much as they, in turn, were suspicious of him. Heisenberg seems to have kept his eye on an eventual resurrection of Germany after having somehow overcome Hitler, and regaining not least, with Heisenberg’s own help, its place in science. So Powers, using his space to reassert the credibility of his old, published thesis of Heisenberg as saboteur, might instead have helped us to explain the trajectory of Heisenberg’s change of mind and mood in those years, from the confident weaponeer and propagandist Bohr understood him to be in September 1941, to his disillusion as the final tragedy unfolded.

Unlike Mr. Powers, Mr. Frayn began his essay with some gracious acknowledgments that some of the criticisms of his plays have substance and could be accepted. He is alert to the fact that when new materials come to light, historical assessments, in which he shows great interest, may have to be reconsidered. In the first postscript (1998) to his published playscript, he explained that what first aroused his interest in the Copenhagen encounter was Thomas Powers’s book, which he called “extraordinary and encyclopedic.” Later, in Postscript II in the edition of 2000, he tells that he came across the Farm Hall Papers in the book published by Bernstein, mentioned above. It opened his eyes to facts he had not known before, and he takes back half of his belief in Powers’s thesis. And now the ever-pregnant muse of history has brought forth yet more documents, and it resulted in his newly published, third postscript.


But Mr. Frayn, while citing passages from Bohr’s documents, as did Mr. Powers, avoided using the extensive space made available to put the two crucial documents in the case side by side for comparison, namely at least the first and longest of Bohr’s drafts on one hand, and on the other hand Heisenberg’s letter to Robert Jungk (in Jungk’s book Brighter than a Thousand Suns, 1958, pp. 102–104), the letter (and book) that informed much of Powers’s ideas. These two documents, in which the two protagonists describe their respective recollections of their 1941 meeting, are fundamentally at odds, Bohr contradicting every major point in Heisenberg’s account.

Instead of providing that service, Mr. Frayn takes umbrage (as he has done elsewhere) with my perception that his play, and especially his first postscript published with it, was closely patterned on the ideas of Mr. Powers. He allows I may have been “misled because in my postscript I speak warmly and gratefully about Powers’s book.” But in his heart of hearts, he avers he does not and never did believe Powers’s thesis about Heisenberg having sabotaged the bomb project.

The vehemence of this attack has puzzled me. But the answer to the puzzle may be that, in pointing out the parallelism I mentioned, I have unwittingly bumped into an old, painful sore from another fight. At any rate, I have no trouble acknowledging that Mr. Frayn’s early, warm embrace of Mr. Powers may have misled me about his true feelings, as it might mislead anyone reading that first postscript. Still, what to do about such lines in his play as “Heisenberg’s” dramatic remarks: “I understood very clearly. I simply didn’t tell the others”? And later: “I wasn’t trying to build a bomb. Thank you.” Perhaps should the actor now deliver the lines with heavy irony?

More problematic still is the second swipe at my previously published remarks that I was a bit startled (as were others in the audience during the play’s performance) to hear Frayn’s Heisenberg exult that his actions or inactions secured him a place in heaven, whereas Niels Bohr by implication seems to be assigned to the other place. A grotesque oversimplification and perversion of the actual moral balance, but all well and good—so long as we remember we are watching a gripping play, which is by definition a piece of fiction in which a good author induces the suspension of disbelief.

But just here we come finally to the tragic flaw with Mr. Frayn’s own perception of his play. As the unusual succession of Mr. Frayn’s postscripts makes clear, he is not satisfied to have Copenhagen be and remain a work of fiction, along the lines of others in the genre such as Bertold Brecht’s Galileo or, for that matter, Shakespeare’s historical dramas—plays that retain their authenticity regardless of how far they diverge from the actual events on which they drew initially for inspiration. On the contrary, Mr. Frayn evidently has an agenda—to make a moral judgment about the actual persons, Heisenberg and Bohr. He speaks now of the audience drawing “its own moral conclusions.” And a recent interview with Mr. Frayn, published in The New York Times (February 9, 2002), goes further. He concludes with his relative moral assessment of the actual, not the fictional persons—one who had in fact been working with varying degrees of enthusiasm for Germany’s war machine, the other who had to flee for his life and came too late to Los Alamos to have a significant technical effect there. Frayn said: “Heisenberg didn’t, in fact, kill anyone…,” whereas Bohr “did actually contribute to the death of many people….”

In short, unlike almost all dramatists, Mr. Frayn wants to have it both ways—a work of fiction and, interspersed with it, a factual documentary with a moral message. But that entails a fundamental conflict. The ever-living volcano of those historic times will continue to emit newly found documents that will keep historians busy, and will also require Mr. Frayn to issue yet more exculpatory postscripts. While I have no standing in Mr. Frayn’s profession, perhaps I may offer him a personal suggestion: the thing’s a play, a fine, award-winning piece of fiction for the theater, a work of great dramatic power. That should be enough. As John Keats wrote in 1817 so memorably, great authors should be “capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason.”

Gerald Holton

Mallinckrodt Professor of Physics and Professor of History of Science Emeritus


Harvard University

Cambridge, Massachusetts

To the Editors:

When, in Michael Frayn’s Copenhagen, Bohr avers that Heisenberg was “ahead of Fermi” in June 1942, the statement is designed to mislead. The implication is that even this late the Germans still had prospects for an atomic bomb. Absent this, Frayn’s Heisenberg could not in good faith have proposed a nuclear “truce” to Bohr. Nor could the necessary illusion be maintained that matters of great consequence teetered anxiously in the balance. In reality, Germany had fallen far behind the Allies by then, with no U-235 or plutonium isolated; a failed isotope separation technology; and a hopelessly discouraging critical mass estimate. Neither the military officials of the Heereswaffenamt nor any informed scientist still believed a bomb was a realistic possibility. One of Heisenberg’s exploratory experiments did yield a higher neutron multiplication factor than Fermi’s; but Fermi, long past such improvisation, was already methodically scaling up the graphite reactor design that, a few months later, produced the world’s first chain reaction.

A more elaborate casuistry underlies the play’s pivotal trope, the fantasy that Heisenberg, checked by unconscious scruple, withheld himself from the critical mass calculation that would have put a bomb in Hitler’s hands. German wartime reports leave no doubt that Heisenberg did do such a calculation, first in a December 1939 technical report and again after realizing that fast neutrons were essential. Like Bohr, Peierls, Flügge, and others who had considered the problem, Heisenberg mistakenly concluded that tons of U-235 would be required. We know the details because the real Heisenberg recapitulated them three times in the Farm Hall reports, in passages Frayn carefully avoids in the thirty-five speeches he devotes to misdirecting us. Before this discouraging result, Heisenberg displayed no detectable reluctance to proceed toward a bomb. The “mysterious” lack of zeal endowed by Frayn and Powers with such significance is no mystery at all.

As to Heisenberg’s hypothetical ascent to heaven, any irony might be easier to detect if so much in the play had not been turned to improving Heisenberg’s chances. Frayn’s Nazis are evil, but offstage, while the suffering of Germany and Heisenberg’s elevated moral agonies are vividly present. Heisenberg’s willing propaganda visits to Nazi-occupied Hungary, Poland, and Holland go unmentioned. The suppression of “Jewish physics” is cited; but only to display Heisenberg as an embattled victim. There is a Gestapo; but Werner Heisenberg is its principal victim. Auschwitz is also invoked; but as an occasion to sow doubt about Goudsmit’s critique of Heisenberg’s easy rationales. The plight of Denmark’s Jews is described; but only to insinuate a (wholly invented) connection for Heisenberg with the anti-Nazi resistance. Strategically supplied just before the elegy of Heisenberg’s perilous journey home through the smoking ruins, this treacly dose of disinformation seems intended to forestall the queasiness a historically informed audience might reasonably feel at this point.

Just before Heisenberg places into heaven himself and the SS man (whom I take to have been inserted to provide “ironic” cover), he has willingly assented to Bohr’s observation that while he himself never contributed to the death of a solitary person, Bohr is complicit “in the deaths of a hundred thousand people.” Any doubt of Frayn’s own, un-ironic investment in this moral inversion was dispelled in a February 9 New York Times interview where Frayn offered up the observation as a reasonable judgment, this time in his own voice.

Jonothan Logan

New York City

Thomas Powers replies:

Before replying to Gerald Holton’s comments in detail I think it would be useful to remind him and interested readers why we are debating Heisenberg’s role in the German bomb program more than fifty years after the end of the war. At the core of the controversy is a problem—facts which do not sit easily together and require explanation. Put briefly, the problem in this case is comprised of the following facts:

The German army was quick to understand that the discovery of fission in early 1939 meant it might be possible to build extremely powerful bombs of a new type. Heisenberg and other scientists were drafted in the first weeks of the war to investigate this possibility and by the turn of the year 1941–1942 had completed the most difficult theoretical work, concluding that the critical mass of fissionable material required for a bomb would be on the order of ten to one hundred kilograms. But despite the success of this early work the German army canceled its program of atomic research in February 1942. Diehard supporters of the program tried to revive it by appealing to Hitler’s newly appointed czar of the economy, Albert Speer, but at a meeting of several score leading military and scientific figures in Berlin in June 1942 Heisenberg argued persuasively, as he had earlier, that building a bomb would be too big, expensive, and uncertain a project for Germany in wartime. Research continued until war’s end on building a reactor, but Germany’s efforts to build an atomic bomb, never large, came to a complete halt in June 1942—the very month, ironically, that the American Manhattan Project got underway.

The argument now is focused not so much on what Heisenberg did as it is on why he did it. It is my belief that Heisenberg and several other scientists stressed the difficulties of a bomb program because they did not want to build a bomb for Hitler. This is not a complicated idea but I can assure readers it has proved to be a controversial one.

In his comments, Gerald Holton misrepresents what I think in two ways. I have never argued that Heisenberg “sabotaged” the German bomb project—a word which suggests skulking at midnight, hiding the blueprints, and putting sugar in gas tanks. Instead, I think he found a way of leading it into a closet where it languished for the remainder of the war as a low-level research effort with the useful side effect of keeping a number of promising young physicists out of the army. Heisenberg did this, in my opinion, by using his authority as a Nobel Prize winner to stress the magnitude of the project, an argument which both the German military and Albert Speer had to take seriously, not least because Heisenberg was its source.

One significant aspect of Heisenberg’s meeting with Bohr in 1941 is what it reveals about his thinking nine months before the meeting with Speer. That Bohr was angry, and that Heisenberg told him about the German bomb program, we have long known. The new Bohr documents confirm and enrich our knowledge of both, but, brief as they are, they certainly cannot “contradict” Heisenberg’s account. If Bohr remembered that Heisenberg had arrived wearing a hat, would that “contradict” Heisenberg’s memory that he was also carrying an umbrella? It was news of the bomb that Bohr remembered, and why Heisenberg told him about it is what historians need to explain.

Holton also suggests wrongly that my book’s “central theme was always that Heisenberg understood all along what had to be done to build a bomb, but kept it secret from everyone….” I do believe that Heisenberg understood how to calculate critical mass—the one relatively difficult theoretical question on the way to building fission bombs—but he certainly did not keep it secret from everyone. He gave a correct figure to both Otto Hahn and Manfred von Ardenne in late 1941, and a February 1942 paper by the German Ordnance Office, summing up research since the beginning of the war, gave a roughly correct figure for critical mass of ten to one hundred kilograms—Heisenberg certainly had not kept the all-important figure secret from the authors of that paper. Nevertheless, some scientists running the atomic research effort at the end of the war did believe the critical mass figure was two tons, and it appears that they got the figure from Heisenberg. For some reason Heisenberg was giving a different estimate for critical mass to different people—“a few kilograms” to Otto Hahn, two tons to Walter Gerlach, titular head of the German research effort in 1945. To me it seems natural to wonder why he did this.

Jonothan Logan, however, is not in a wondering mood. The tenor of his letter—“designed to mislead,” “elaborate casuistry,” “insinuate,” “treacly dose of disinformation,” “queasiness”—hardly seems intended to invite conversation. It is evident he doesn’t like Michael Frayn’s play; but his only substantive point is the claim that Heisenberg came up with a figure of tons in a December 1939 technical report on reactor design. I do not think Logan is right about this, but even if he were it would not negate the evidence already cited above that Heisenberg had calculated an accurate figure in 1941. It would only show that Heisenberg was giving a different figure to different people at the beginning of the war, as well as at the end.

Finally, Michael Frayn did indeed, as Holton says, remark in an earlier essay that I had not persuaded any historian to agree with my conclusions about Heisenberg—something I had told him. What I meant was simple enough: none of the eight or ten historians who have worked on this question abandoned previous positions to adopt mine. David Cassidy, Heisenberg’s biographer, warned me at an early stage that opinions about Heisenberg were set in concrete and nothing I wrote would be likely to change them. I blush to admit I hoped otherwise because I felt I had found so much new evidence. But Cassidy was right. As a result, when I debate Holton or others I try but do not expect to bring them around on a point or two, but at the same time I am trying just as hard, with more hope, simply to arouse the curiosity of those listening in.

Curiosity is the essential ingredient. If I have a quarrel with Holton it is that he appears to lack curiosity. He tells us that he had “several pleasant meetings” with Heisenberg after the war but apparently never asked him about the already famous meeting with Bohr in Copenhagen in 1941. In fairness, Holton isn’t the only one; many scientists were too shy to ask either Heisenberg or Bohr about the exchange. But in his comments now Holton does not even appear to share the curiosity of Bohr, expressed in the last versions of his unsent letters, where he wonders “what authorization might have been given to you by the German government to touch upon such a dangerous question….” Holton is a historian of science, and I hope Bohr’s question will not only arouse Holton’s curiosity, but that he will even make an effort to find out the answer.

Michael Frayn replies:

I’m pleased that Jonothan Logan now accepts that Heisenberg in June 1942 was ahead of Fermi in terms of neutron multiplication, but I’m baffled by his suggestion that the play is in any way trying to obscure or detract from Fermi’s overall success. I’m even more baffled by his suggestion that I’m using this brief lead to support Heisenberg’s claim that he hoped to propose some kind of physicists’ understanding to Bohr. The meeting with Bohr had already occurred nine months earlier, and Bohr agrees that Heisenberg indicated to him the point at issue—the existence of a nuclear weapons program in Germany.

Jonothan Logan and Professor Holton are of course entitled to their idiosyncratic perceptions of my play. I’ve already commented on the specific objections raised once again by Holton, and I’ve already offered in the postscript to the text a brief but I hope fair summary of the conflicting evidence for whether Heisenberg had ever made a serious attempt at calculating the critical mass, and if so with what result. Logan, though, seems to be suggesting that Heisenberg’s encounter with the SS man is my invention. Not so; it’s based on what Heisenberg told his wife.

Holton and Logan both seem to have objections to my mentioning that Bohr was involved in the production of the bombs that succeeded in killing 100,000 people. I’m not clear, though, whether they are disputing the fact of his involvement (peripheral but not nugatory, as the play makes clear), or the (very conservative) estimate of the casualties, or simply my referring to the matter at all.

This Issue

April 11, 2002