Absence of A-bomb
Were the Nazis duped–or simply dumb?

BY WARREN P. STROBEL

'But why?... Why did he come to Copenhagen?" With that pregnant question, Michael Frayn's Tony Award-winning play opens. Copenhagen has revived a mystery so raw it still moves historians and physicists to flights of rage. Why did Hitler's Germany fail, utterly, to develop nuclear weapons? And why did brilliant physicist Werner Heisenberg, a central figure in Germany's nuclear research, visit Nobel laureate Niels Bohr in occupied Denmark in September 1941? Did he go as a loyal German, to learn how much Bohr (and the Allies) knew about atom bombs? Or as a scientist-hero, trying to stall Nazi research and naively hoping to persuade Bohr to restrain the Allies?

After a German and an Austrian discovered fission in 1938, almost everyone thought Germany would be the first to build nuclear weapons. In August 1939, Albert Einstein warned President Roosevelt of the threat. Dread of a Nazi A-bomb drove the Manhattan Project. Yet an Allied mission code-named Alsos, following on the heels of troops liberating Europe, found only a primitive program. No working nuclear reactor. No large quantities of separated Uranium-235, a basic bomb ingredient. No credible bomb design. "Sometimes we wondered if our government had not spent more money on our intelligence mission than the Germans spent on their whole project," wrote Alsos scientific director Samuel Goudsmit.

Uncertain man. To understand Germany's failure, historians (and playwright Frayn) focus on the enigma that is Heisenberg. The brash German patriot was just 32 when he won the Nobel Prize for the uncertainty principle, which states that it is possible to know a subatomic particle's position or momentum, but not both. In simplified form, the principle means that the very act of observing something changes its behavior.

"Uncertainty" is the leitmotif of Heisenberg's life. Touring the United States in the summer of 1939, he had offers of refuge but returned home. He regarded Hitler as a thug and transitional figure, and said he stayed to salvage German science for later. After the war, most physicists in America reviled his attempts to justify himself–and the mysterious wartime trip to Copenhagen to talk about fission with Bohr. He died in 1976. "Time and time again I've explained it," Frayn's Heisenberg laments from beyond the grave. "To interrogators and intelligence officers, to journalists and historians. The more I've explained, the deeper the uncertainty has become."

Frayn's play reignites the animosities. "It has to do with Nazis and atomic bombs, so emotions are dredged up," says Heisenberg biographer David Cassidy. After all, if Heisenberg and the Germans never got close to the bomb, what does that say about those who did build–and use–it?

There are many possible explanations of the German failure, and Heisenberg's actions. But then the questions cascade like neutrons in a chain reaction. If Heisenberg wanted to build a bomb, say his sympathizers, he would have sold the powerful Nazi armaments minister Albert Speer on the idea at a key June 1942 briefing. By then, German physicists realized that if they constructed a nuclear reactor, it would make plutonium, a substitute bomb fuel for U-235, which was hellishly hard to separate from natural uranium. Yet Heisenberg downplayed hopes of making a bomb and asked Speer for a paltry few million marks for research. His bomb program coasted. Overseeing nuclear research was merely a means for Heisenberg to rehabilitate himself, Cassidy says. Nazi fanatics had called him a "white Jew" because of his links with Einstein's physics.

Mind reader. Copenhagen is based on the 1993 book Heisenberg's War. Author Thomas Powers argues that the physicist heroically hid key calculations proving a bomb was possible. Frayn, whose play is largely sympathetic to Heisenberg, won't go as far: "It's a question of what was going on in Heisenberg's mind."

Or perhaps the German didn't want to promise a bomb he couldn't deliver. A brilliant theorist, Heisenberg was a lousy engineer who often had trouble with basic calculations. After Germany's defeat, Heisenberg and nine colleagues were interned at Farm Hall, a British country house. Hidden microphones recorded their stunned reaction to the U.S. atomic bombing of Hiroshima. The tapes, released in 1992, reveal a Heisenberg who did not understand bomb physics and vastly overestimated how much U-235 was needed for "critical mass." "You're just second-raters and you might as well pack up," a colleague gibed on the tapes.

So why did Heisenberg come to Copenhagen? By September 1941, he knew nuclear weapons were a theoretical possibility for Germany–and its enemies. He raised the subject with Bohr, who was horrified at Heisenberg's hint. Their pre-war friendship was shattered. In a postwar letter to journalist Robert Jungk, Heisenberg wrote that he merely wanted to discuss physicists' ethical responsibilities. Jungk later concluded he had been duped by Heisenberg and other German scientists trying to justify their actions.

The visit was "an intelligence mission, nothing more or less," agrees Manhattan Project physicist Arnold Kramish. Two weeks before, a Swedish newspaper had published news of U.S. bomb research. Heisenberg wanted to learn more from his former teacher. Bohr himself disputed Heisenberg's account of the meeting in a letter so angry he never mailed it. Gerald Holton, a Harvard University historian of science who has seen the letter, says it takes "serious issue" with Heisenberg's claims. It will be made public in 2012, the 50th anniversary of Bohr's death.