Review -- Heisenberg’s War: The Secret History of the German Atomic Bomb

Heisenberg’s War: The Secret History of the German Atomic Bomb

by Thomas Powers

A Founder of Modern Physics

By the late 1930s Werner Heisenberg’s fame as one of the founders of modern physics was firmly established. His paper on the “uncertainty principle,” published when he was 26, revealed an amazing, fundamental feature of the subatomic world. Our knowledge of the physical world, he announced, would never be complete, because in principle it is not possible to know both the position and momentum of a particle (or better, that the more precisely we know its position, the less precisely we can know its momentum, and vice versa). In 1932 he was awarded the Nobel Prize for Physics "for the creation of quantum mechanics." His work, combined with that of his mentor and friend, the towering figure of Niels Bohr, formed the background to a series of historic debates Bohr held with Einstein about how to make sense of the bizarre findings of modern quantum mechanics. While Einstein argued powerfully for the idea that fundamentally the physical universe is comprehensible, governed by causality and predictability, that “God does not play dice with the universe,” Bohr, to the satisfaction of most physicists, refuted him, arguing for the “Copenhagen interpretation” of quantum mechanics, an idea he shared with Heisenberg, the view that the physical world is indeterminate, governed not by certainties and traditional causality but ultimately by probabilities.

On a tour of America in the summer of 1939 Heisenberg was repeatedly invited by various scientists he met there to emigrate, as many of them had done, and make a clean break from Hitler’s Germany. While despising Nazism, Heisenberg felt bound by a deep loyalty to his native country and replied rather optimistically that he was needed at home to offer a voice of reason, to “create islands of decency,” to protect young German scientists from conscription, and to keep German science on the right path in the face of appalling nonsense about “Jewish science.”

The Most Dangerous Man in Germany

A month after his return home hostilities broke out, and soon thereafter Heisenberg was made leader of atomic research in Germany. Although scientists outside Germany struggled to maintain contacts, friendships, and a semblance of internationalism, their efforts wobbled under the pressures of war. To some, Heisenberg, who they feared might put an atomic bomb in the hands of Hitler, became “the most dangerous man in Germany because of his brain power.” Ever since, suspicion has hung over his name. How morally compromised was he by working under the Nazis? How committed was he to developing a German atomic bomb? How far did the project get? And even—was the failure of Germany to produce an atom bomb the result of his scientific incompetence?

In Heisenberg’s War: The Secret History of the German Atomic Bomb, a work of extraordinarily detailed research, Thomas Powers sorts through a vast range of sources to answer those key questions. The weighing of evidence is subtle and complex, but the conclusions Powers comes to are clear.

Hero or Traitor?

Powers provides evidence that Heisenberg did deliberately prevent Germany from working on an atomic bomb, although after the war he was not entirely forthcoming about his role. In the early years of fission research, soon after it was discovered in 1939 by Otto Hahn, all scientists acknowledged that, if a bomb were feasible, developing it would require a gargantuan, resource-draining effort. As the war began, German scientists agreed that such an effort would take too long to produce results before the war was over. In June 1942 Albert Speer called a crucial meeting between government officials and scientists to determine whether Germany should pursue an atomic bomb (about the same time, incidentally, that the Manhattan Project got underway). Heisenberg addressed the meeting, clearly spelling out all the difficulties. Soon afterward, all work on a German atomic bomb came to an end, with nuclear research restricted to small-scale work on an “energy machine” or reactor. Heisenberg had managed, in Powers’s words, “to guide German atomic research into a broom closet where scientists tinkered until the end of the war.” Germany’s stockpile of uranium was used to make armour-piercing shells.

Was Heisenberg simply being realistic in his assessment for Speer, or was he deliberately discouraging bomb development? After the war Heisenberg maintained that he had honestly believed a bomb to be impractical at the time, adding that German scientists were thus “spared the moral decision” of whether to work on a bomb. (On August 6, 1945 he and the other German scientists being held in detention in Britain were stunned by the news of the Hiroshima attack, shocked that American scientists had worked on the bomb and horrified that President Truman had used it to destroy a city.) Yet Powers points out that Heisenberg’s post-war account omitted important details. What he had told Speer may not have been untruthful, but it was carefully crafted to dampen interest. While outlining the extreme difficulties of separating the fissionable U-235 isotope from uranium, Heisenberg did not mention the relatively easier path to a bomb using plutonium. Asked whether a nuclear explosion might set the entire world on fire, he did not rule it out as a possibility. His talk emphasized all the difficulties and, most important of all, buried in technical language the most alarming possibility, the mere fact that there was an outside chance that someone—if not Germans, then Americans—might build a bomb for use in the war. Phrased differently, his presentation could have put Speer on high alert and ensured that Germany would set to work full bore on an atomic bomb. The crucial moral decision had, in fact, been made by Heisenberg and his colleagues, and they had chosen to block Hitler. His fudging of that fact after the war was probably an attempt to escape being branded a traitor by some of his countrymen.

During the war Heisenberg made a number of very risky efforts to let Allied scientists know that Germany was not working on a bomb. His intention—his “vague hope,” as his wife described it—was that he might inspire all scientists everywhere to refuse to work on a bomb, thus preventing the horror of a world armed with nuclear weapons. The hope, however, was as naive as it was vague. Americans, especially the émigré scientists who had fled Nazism, distrusted him for remaining behind, wondering whether his assurances were aimed at stopping Allied efforts, thus clearing the way for Germany to become the sole nuclear power. The mere mention of a bomb by Heisenberg prompted the Allies to undertake the most intense efforts to find information about a German bomb program—the American effort, under General Groves, chief of the Manhattan Project, never relaxing an iota until Germany was occupied and its last laboratory was inspected.

Kill or Kidnap?

In its 500 pages Heisenberg’s War covers a great deal of material other than Heisenberg and the moral culpability question. The SS came close to arresting him twice. There is the adventure-movie story of the attacks on the heavy water production facility in Norway (“The Heavy Water War,” a Norwegian series on Netflix gives a too-dark portrayal of Heisenberg).  Heisenberg’s famous visit to Bohr in 1941 is given close scrutiny. The visit led to such a chill in their relations that it never fully rewarmed; it has been the subject of endless comment, including in the 1998 play “Copenhagan.” Powers’s conclusion is that the break occurred, first, because Bohr was shocked to hear his old friend speaking of atomic bombs and, second, because he was deeply angered by several pro-German remarks Heisenberg made about the necessity of occupying various European countries, including Denmark, and the great good Germany was doing for Europe by attacking Russia. With supreme insensitivity he once remarked how much better off Europe would be dominated by Germany than dominated by Russia.

One thread that runs through many chapters is the deep concern the Allies had over what to do about Heisenberg. A first step was to determine the exact nature of his research projects, leading to several fascinating cloak-and-dagger operations involving more than one outlandish character. By the summer of 1943 the British reached the conclusion that there was no German atomic bomb program, mainly on information coming from their contacts with scientists in neutral countries who were still in touch with sympathetic German scientists, but also because the code breakers at Bletchley Park had never deciphered a single message referring to atomic bombs or Heisenberg. Because the Brits shared their conclusion but not their sources, they failed to convince the Americans, who remained implacable. Robert Oppenheimer’s opinion was that Heisenberg should be killed. General Groves considered recommending a bombing raid on Heisenberg’s lab in Berlin with the object of killing the scientists. More elaborate and enduring were several plans to kidnap Heisenberg as he attended a conference in Switzerland. At one point, an agent with a pistol in his pocket sat in the front row of a lecture hall as Heisenberg talked, ready to shoot him if he dropped the slightest hint about a German atomic bomb.

After Germany was occupied, the Allies were stunned to realize the primitive stage of German nuclear research, and the story was born that Heisenberg and his team had made grave scientific blunders. On the night of Hiroshima, Otto Hahn, in detention with them, called them “second-raters.” (Hahn himself was on the verge of suicide over his discovery of fission.) Power spends about ten pages considering the evidence before finally concluding that Heisenberg’s apparent mistakes were really a ruse to prevent the development of a bomb. He knew the world’s most dangerous secret, and he kept it from even his closest colleagues.