POSTSCRIPT

In 1954, the year before he died, Einstein was visited in Princeton by Heisenberg, just for a few hours. The old man was clearly sinking. He was seventy-five, and had known for some years that an abdominal aneurysm was swelling slowly within him. Surgery would have been risky, and Einstein saw no point in trying to stave off the inevitable. He had suffered through a bout of anemia but recovered. When Heisenberg came by, they spoke politely of small matters. Not about the war, and not much about quantum mechanics. “I don’t like your kind of physics,” Einstein told his visitor. “There’s consistency, but I don’t like it.”

The war had further strained an already distant relationship. Einstein, of course, signed the famous letter to President Roosevelt outlining the possibility of an atomic bomb, but took no part

in designing or building it. Bohr had stayed in German-occupied Copenhagen as long as he could before being spirited away, almost fatally, by the Royal Air Force. Although he had written about the physics of fission, Bohr played only an indirect role in the Manhattan Project.

Heisenberg, meanwhile, remained in Germany. His disastrous visit to Bohr in 1941, which broke any remaining friendship between the two men, is the pivot of Michael Frayn’s sharp and melancholy play Copenhagen. There was some sort of German project to make use of nuclear power; Heisenberg was involved; he sounded out Bohr—perhaps—on some aspects of the relevant physics.

Bohr’s wife said that there was always an aloofness, a distance, to Heisenberg’s relationships. Her husband had had awkward moments with Heisenberg, she said, but “in between he was a pleasant man...He was what you call well-bred. I mean he had nice manners and was pleasant in that way. But there were difficulties with Heisenberg.” He had always been a shy, reserved, formal man and never warmed up fully to others. Dirac, hardly the most sociable type himself, found Bohr easy to get on with, thought the waspish Pauli positively amiable, but remained a little uncomfortable around Heisenberg.

What Germany’s wartime nuclear program accomplished, or what it tried to, has never become entirely clear. The country was depleted of resources, including intellectual resources, as so many of the physicists nurtured there had been hounded out. Heisenberg, undoubtedly one of the great innovators and conceptualizers in theoretical physics, was not the man to do practical nuclear physics or engineering. It appears he never figured out correctly how a bomb would work and thought a ton of uranium would be needed. Later, in ugly fashion, this failure transmuted into a story that the Germans, meaning in particular

Heisenberg, had turned away from the moral repugnance of building atomic weapons, or had even deliberately misled their political superiors about the feasibility of doing so. Heisenberg never exactly said this. He never exactly denied it.

Many physicists shunned Heisenberg after the war. Bohr tried to be at least cordial. Slowly, Heisenberg worked his way back into the scientific community, eventually becoming director of the Max Planck Institute in Munich. Einstein was long gone by then. Pauli died suddenly in 1958, Bohr in 1962. Heisenberg died in Munich in 1976.