Copenhagen - Michael Frayn [47]
After the war, certainly, Heisenberg was not just passively reluctant about any military application of nuclear power, but very actively so. In the 1950s, when there was a proposal to arm Federal Germany with nuclear weapons, he joined forces with Weizsäcker and others to fight a vigorous campaign that entirely and permanently defeated it.
There is also one small piece of evidence about his attitude during the war that Powers rather curiously doesn’t comment on: the question of the cyclotron.
At the crucial meeting between Heisenberg and Speer in 1942, which seems finally to have scuppered all possibility of a German bomb, Heisenberg is reported to have emphasised the need to build a cyclotron. A cyclotron could have been used, as the cyclotrons in America were, for isotope separation, the great sticking-point in the German programme. In the account of this meeting in his memoirs Speer says: ‘Difficulties were compounded, Heisenberg explained, by the fact that Europe possessed only one cyclotron, and that of minimal capacity. Moreover, it was located in Paris and because of the need for secrecy could not be used to full advantage.’ Powers mentions this, but does not go on to the obvious corollary: that if Speer’s recollection is accurate, then Heisenberg was plainly lying, because he knew perfectly well that there was a second cyclotron to hand—at Bohr’s institute in Copenhagen. This would suggest that his apparent anxiety to lay his hands on a machine that might actually separate some U235 was not quite what it seemed. Or, at the very least, that he placed Germany’s war aims below his desire to protect Bohr’s institute.
Perhaps Speer is simply wrong. It seems uncharacteristic of Heisenberg to have risked such a blatant falsehood, and he makes no mention of it in his own accounts of the meeting. All the same, when he went back to Copenhagen in 1944, after Bohr had fled, to adjudicate a German proposal to strip the institute of all its equipment, presumably including the cyclotron, he seems to have contrived to leave it even then still in Danish hands.
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One of the forms of indeterminacy touched upon in the play is the indeterminacy of human memory, or at any rate the indeterminability of the historical record. There are various examples which I left out, for fear of making the play even more tangled than it is. Some, such as the difficulties about the amazingly realistic figure for the critical mass that von Ardernne recollected being given by Heisenberg and Hahn in 1941, I have already mentioned in this Postscript. There were others. A minor one concerns whether there were two ships sent to load the Jews of Copenhagen for deportation, as some witnesses recall, or a single one (named as the Wartheland). A more significant point of dispute is the drawing which Heisenberg did or didn’t make for Bohr during their meeting in 1941.
According to Hans Bethe, who was one of the team at Los Alamos, Heisenberg drew a rough sketch to show Bohr the work that was being done in Germany. Bohr evidently took it to Los Alamos with him when he went, because Bethe (and others) recall it being passed around at a meeting there. Bethe told Powers that Bohr believed it represented a bomb; but the consensus of opinion at the meeting was that it was a reactor. However, Aage Bohr, Niels’s son, a physicist himself (and another Nobel prizewinner), who was with his father in Copenhagen during Heisenberg