Source: The New York review of Books

Almost as soon as World War II ended in Europe, and with redoubled intensity after the bombing of Hiroshima, physicists all over the world began to ask how close the Germans had come to making an atomic bomb. But it was not clear whom to ask. Everything to do with development of the bomb was cloaked in secrecy and ten of the leading scientists involved in German atomic research had gone missing. One of them, Otto Hahn, the first to explain the fission process that made bombs possible, was on November 15, 1945, awarded the Nobel Prize in chemistry for his discovery, but the prize committee, it turned out, had no idea where Hahn was.

Among the few who did know were leading scientists who had developed the American bomb at Los Alamos in New Mexico. Many of them were Jews by Nazi standards who had fled Hitler’s Germany, including the physicists Hans Bethe and Victor Weisskopf, who had feared at the beginning of the war that the great German theoretical physicist Werner Heisenberg would build a bomb for Hitler. In 1942, learning that Heisenberg was going to give a scientific talk in Zurich, Bethe and Weisskopf had proposed an American operation to kidnap Heisenberg in Switzerland and even offered to take part themselves. This episode, improbable as it sounds, has been well documented elsewhere¹ and after many twists and turns the original proposal led to Heisenberg’s detention in southern Germany in May 1945.

By November, Heisenberg, Hahn, and the other German scientists were being secretly held and closely monitored at a British country house called Farm Hall. The man who had the most to do with putting them there was the Dutch-born physicist Samuel Goudsmit, scientific director of an intelligence group called the Alsos mission. Goudsmit’s task was to track down the Germans who had been working on nuclear fission during the war and to answer the basic question—how close did the Germans get?

For the first year or two after the war pretty much everything Bethe and Weisskopf knew about the answer to the basic question came from information supplied by Goudsmit, a colleague in the Manhattan Project. The answer was not close at all. The Alsos mission found nothing that ever posed a threat to the Allies—instead there was a scattered program of small-scale, poorly funded research efforts that centered on an experimental reactor hidden in a cave in southern Germany that Heisenberg mistakenly hoped would soon be successful. When he first talked to Heisenberg in May 1945, Goudsmit had been privately scornful of German efforts that had achieved so little, and he dismissed Heisenberg’s attempts to explain the history of that little as the excuse-making of a scientist guilty of crude errors about the physics and technical construction of bombs. Freed by the British in early 1946, Heisenberg insisted for a time that it was all more complicated than that—the Germans, he said, had been spared the moral dilemma of whether to build a bomb because the job was just too big for Germany in wartime.

American officials discouraged talk of moral dilemmas, and lost interest in the basic question once Goudsmit and the Alsos mission had established that the Germans had no bombs or prototypes, no working reactors or stockpiles of plutonium and uranium-235, no community of scientists with bomb-making expertise who might work for the Russians. But Bethe and Weisskopf were different. As scientists, as pre-war friends of Heisenberg, and even as fellow bomb-makers, Bethe and Weisskopf might have been expected to ask more questions of Heisenberg, but as soon as the basic question was answered—not close at all!—their curiosity died.

In 1948, Bethe visited Heisenberg in Göttingen, in the British zone, where Heisenberg and his colleagues were again doing physics. Their talk was friendly enough, Bethe told me, but he held his own curiosity in check and let the moment pass without asking any of the questions that might have helped explain the German “failure.”

Weisskopf did likewise. In the fall of 1948 he exchanged many letters with Goudsmit, who was still trying to sort out why Heisenberg “failed,” but Weisskopf had tired of the whole discussion. “Let’s stop this useless prying into the past,” he wrote Goudsmit, adding that he wanted to tell Heisenberg the same thing. “I would make only one point, but this very strongly: stop prying into the past.”

Heisenberg was certainly the man to ask but his death in 1976 closed that door for good. The mystery of Heisenberg’s “failure” was deepened by the fact that surviving German war records provided no explanation why the program to build a bomb had been radically scaled back—essentially shut down—in 1942. Germany had begun with many advantages—first-rate scientists, the technical expertise and big economy needed for a huge industrial project, access to uranium ore in Czechoslovakia, and above all the enthusiasm of the Heereswaffenamt, the German army’s division for weapons development, which had a bomb project underway on the first day of the war, three years before the Americans got moving. The best explanation—indeed the only explanation—for the about-face in 1942 came from Hitler’s economics czar, Albert Speer, who told the German magazine Der Spiegel in 1967 that Heisenberg had convinced him that building a bomb was too big a project for Germany in wartime:

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