Uncertainty and the Bomb

Posted on August 9, 2002

I’ve just finished reading Michael Frayn’s outstanding play Copenhagen, and I can’t recommend it highly enough. It’s the story of two men, Niels Bohr and Werner Heisenberg — both eminent physicists whose work formed the basis for our modern understanding of atomic physics — and a meeting they had in 1941, after their collaboration had been torn asunder when World War II put their countries on opposite sides (Heisenberg was a proud German, Bohr a half-Jewish Dane). They never revealed what went on at that meeting.

Why should we care? Because Heisenberg had just been made the head of the Nazi program to develop an atomic bomb. That program ultimately failed. But why Heisenberg would choose that moment to meet with his old mentor, a sworn enemy of the Nazi regime, has interested historians and scientists alike ever since. Was he trying to enlist his help in the German atomic program? Or was he trying to warn the Allies — he knew Bohr had contacts in the Danish Resistance — of its existence?

We’ll never know for certain. But Frayn takes us inside that meeting, looking at it from every angle, until we know the two men — and the terrible dilemmas they faced that day.

For Bohr, the danger was immediate and real — he was being watched by the Gestapo (by the time of their meeting, Denmark had been overrun by the Nazis, and Bohr was only allowed to continue his work in physics — regarded by Hitler as the “Jewish science” — by the tolerance of the local German officials). To be given such knowledge by Heisenberg could mean death. Even in 1941, every Jew in Europe knew that the Nazis could truck them off to extermination at the slightest excuse, and this was far more than a slight excuse.

For Heisenberg, the threat was more intricate. The Nazi high command trusted him, and he knew that, so his life was not generally in danger. However, if it was thought that he’d spilled the beans on Hitler’s atomic secret, that trust would evaporate like morning mist. Moreover, he wanted more than anything to be able to continue working on atomic physics — and in Hitler’s Germany, that meant working on the bomb.

That neither he nor Bohr wanted such a weapon to ever be built is disputed by no one. But Bohr did not have to confront the moral dilemma that Heisenberg did. Heisenberg was no Nazi — his friendship and collaboration with the Jewish Bohr proves that. But he did love Germany, and he wanted to see Germany grow strong again after the humiliation of World War I. And he loved atomic physics, a field which he and Bohr had revolutionized with their discoveries of the uncertainty and complementarity principles, keystones of what became the orthodox understanding of modern physics.

So how could Heisenberg reconcile these desires? This was the paradox that gives meaning to their meeting. Did Heisenberg want to build a bomb but found himself stuck, hoping his mentor could resolve a knotty problem? Did he not want to build a bomb, and hold back key information from the rest of his team to ensure that they would not succeed? The motives of Heisenberg are the x-factor in this story, and they are what gives Frayn’s play its teeth. It’s no accident, suggests Frayn, that a man like Heisenberg, a man who could live with such contradictions, would be the one to discover the uncertainty principle, which posits that the more precisely you observe the precision of a particle, the less precisely you can ever know its momentum.

Whole books can, and have, been written about Heisenberg alone. But the thorny relationship between he and Bohr is a subject that makes for compelling drama. Did Heisenberg save the world by sabotaging the Nazi bomb? Did Bohr save the world by not showing Heisenberg the errors that were perhaps preventing him from building such a bomb? Whatever really happened that night in Copenhagen, it’s clear that it was a momentous meeting, and we have Frayn to thank for giving us the chance to sit in.