Werner Heisenberg

Werner Heisenberg was one of the leading architects of quantum mechanics and, during the Second World War, the German physicist whose work and loyalties became a focus of Allied anxiety. His story in American Prometheus turns on that stark change of setting: the young theorist whose discoveries helped reshape physics became, in wartime, a possible rival in the race toward an atomic weapon, while the meaning of his conduct remained unresolved.

A Young Architect of Quantum Mechanics

Heisenberg entered the book’s scientific story as part of a European generation remaking physics. In the early 1920s, he and Niels Bohr were among the physicists building quantum theory, a framework for understanding matter at the scale of atoms and molecules. By 1925, Heisenberg had formulated matrix mechanics, an intensely mathematical account of quantum phenomena. The work was so unfamiliar that Max Born, sending it to Albert Einstein, felt obliged to describe it as looking mystical even while asserting its depth and correctness. Einstein remained unconvinced, but the paper became one of the breakthroughs around which the new physics cohered.

The pace of change was extraordinary. Between 1925 and 1927, researchers developed a radical, more cohesive quantum theory, and Göttingen became one of its principal centers. Heisenberg was only twenty-four in 1926, among a cohort of unusually young contributors whom Wolfgang Pauli nicknamed the boys of physics. The nickname captured both the field’s youthful authorship and its break with an older scientific order. Yet the breakthroughs did not command universal assent: Einstein’s skepticism persisted, sharpened by Heisenberg’s account of uncertainty and the limits on simultaneously determining a particle’s precise position and momentum.

J. Robert Oppenheimer arrived at Cambridge initially without a grasp of quantum mechanics or electron spin; he later recalled that he learned both only after reaching Europe. In 1926, reading Heisenberg’s work alongside Erwin Schrödinger’s wave mechanics, Oppenheimer suspected that the two mathematical approaches were connected. They were, in fact, different formulations of the same theory. Heisenberg’s work thus helped draw Oppenheimer into the central intellectual problem of his early career, and Oppenheimer’s later research repeatedly built on discoveries made by Heisenberg and other European theorists.

An Encounter of Equals and Rivals

When Heisenberg passed through Göttingen in 1927, Oppenheimer made a point of meeting him. Heisenberg was three years older, articulate, charming, and tenacious in argument. The book presents the two young physicists as intellectual counterparts, each conscious of his own originality, while emphasizing that Oppenheimer admired Heisenberg and respected his science. They did not become close friends; their connection was one of mutual, somewhat reserved regard.

That regard had an immediate scientific dimension. Prompted by a remark from Heisenberg, Oppenheimer turned to the question of how quantum theory could explain why molecules held together. He quickly found a solution, showed his notes to Born, and collaborated with him on a paper. The episode places Heisenberg not merely among the famous names in Oppenheimer’s European education but in the chain of ideas that helped direct Oppenheimer’s research.

In 1927, Oppenheimer also visited Leipzig and heard Heisenberg lecture on ferromagnetism. By then, Heisenberg had studied with Wolfgang Pauli at the University of Munich and pursued postdoctoral work with both Bohr and Born. He and Oppenheimer shared a capacity for using intuition to get to the heart of a problem. The book foreshadows the distance that war would put between them: the physicist Oppenheimer admired in Göttingen would later become a figure whose wartime choices he had to scrutinize.

The German Project and the Question of Loyalty

In late October 1942, Oppenheimer received a secret letter from Victor Weisskopf reporting that Heisenberg had been appointed director of the Kaiser-Wilhelm Institute, a nuclear research facility in Berlin, and was scheduled to lecture in Switzerland. Weisskopf, after discussing the news with Hans Bethe, proposed kidnapping Heisenberg there and volunteered to take part. The proposal reflected the fear that Heisenberg’s standing and expertise might contribute to a German atomic effort; it was not evidence that the Allies knew what he intended or what Germany could actually build.

Oppenheimer replied that he had already discussed Heisenberg’s planned visit with authorities in Washington. He passed Weisskopf’s letter to Vannevar Bush and Leslie Groves, but did not endorse the kidnapping. A successful operation, he reasoned, could alert the Nazi government to the importance the Allies attached to nuclear research. At the same time, he told Bush that the visit appeared to offer an unusual opportunity. His response held strategic interest and caution together: Heisenberg mattered enough to watch, but an attempt to seize him could itself increase the danger.

The idea did not end with that exchange. In 1944, Groves pursued the possibility of kidnapping or assassinating Heisenberg and sent OSS agent Moe Berg to Switzerland. Berg, a former baseball player, stalked the German physicist in December but did not attempt an assassination. The episode shows how Heisenberg’s scientific identity had become entangled with intelligence operations and the fear of a German weapon, even though the book does not present him as knowing of these Allied plans.

Copenhagen: A Message That Could Not Be Settled

The deepest uncertainty around Heisenberg centers on his September 1941 meeting with his former teacher and friend Niels Bohr in German-occupied Copenhagen. Bohr later described the encounter to scientists at Los Alamos. Heisenberg had received special permission from the Nazi regime to attend a conference and sought Bohr out. He was a German patriot who had remained in Nazi Germany, and, as the country’s most eminent physicist, was an obvious candidate to lead any German atomic project.

Heisenberg later maintained that he had cautiously raised the uranium problem to suggest that a fission weapon was possible but would demand a tremendous technical effort, one that he hoped could not be achieved during the war. According to this account, he meant to imply that German physicists hoped to dissuade the regime from pursuing a weapon, but feared surveillance and could not say so explicitly. Bohr heard something very different: Germany’s leading physicist, he believed, had said that an atomic weapon was feasible and could decide the war. Alarmed, Bohr cut the conversation short.

Bohr’s recollections did not resolve what Heisenberg meant. In drafts of an unsent letter written years later, Bohr recalled Heisenberg saying that he was certain the war would be decided by atomic weapons if it lasted long enough, and then describing his own sustained work on the question. Bohr’s drafts made clear how shocking the mention of atomic weapons had been to him, but they could not establish Heisenberg’s intention. Oppenheimer later characterized the meeting, as Bohr understood it, as a standoff: Heisenberg and his colleague Carl Friedrich von Weizsäcker might have been trying to discover what Bohr knew rather than simply convey what they knew themselves.

From Wartime Fear to a Lasting Enigma

When Bohr arrived at Los Alamos on December 30, 1943, he warned Oppenheimer and the laboratory’s senior scientists that Heisenberg was working on a uranium reactor capable of producing a runaway chain reaction. Bohr also showed them a drawing he said Heisenberg had made of a bomb. On inspection, the drawing appeared to depict a reactor, not a bomb. Hans Bethe joked that the Germans seemed to be trying to throw a reactor at London; the scientists concluded that the design described would be militarily useless. Oppenheimer subsequently told Groves that an exploding uranium pile would not make an effective military weapon.

The distinction mattered. Bohr had come away from Copenhagen fearful that Germany might build an atomic weapon; the Los Alamos scientists, confronted with his report and drawing, found reason to think the specific design was impractical. Neither reaction settled what Heisenberg had intended in 1941, or what Germany’s broader efforts amounted to. The meeting remained controversial precisely because the accounts could not be made to coincide with confidence.

Heisenberg’s place in Oppenheimer’s life therefore changes without becoming simple. In the scientific narrative, he is a brilliant contemporary whose work helped open quantum mechanics and whose ideas Oppenheimer extended. In the wartime narrative, he is a possible adversary, a subject of proposed abduction, and the absent half of an encounter remembered through Bohr’s uncertain testimony. The book preserves that contrast rather than supplying a definitive judgment: Heisenberg’s scientific importance is clear, while his wartime purpose remains an enigma.