Re-"Creating Copenhagen" at CUNY Symposium

Hans Bethe (right) picks up some acting tips from Michael Blakemore. Photo by Gerald Cyrus

Why did Werner Heisenberg make the risky journey to Copenhagen in 1941 to visit his former mentor, Niels Bohr? What did the two discuss, and why did it end their friendship? Was Heisenberg trying to learn about Allied progress on the atomic bomb? Was he seeking Bohr's input on the ethics of applying physics to construct a weapon of mass destruction? And should history view Heisenberg as a hero for purposely slowing or sabotaging the German bomb effort, or an incompetent engineer who failed to understand the key design principles involved?

These unsolved mysteries provided the thematic framework for a special symposium in March, sponsored by the City University of New York Graduate Center, entitled "Creating Copenhagen." Both the American Physical Society and the American Institute of Physics were co-sponsors of this event. Physicists, historians, theater professionals, and members of the general public alike crowded into the new Proshansky Auditorium for the free, day-long series of events, which included lectures on the science and history of the so-called "Copenhagen Interpretation" of quantum mechanics and the subsequent development of the atomic bomb.

The CUNY symposium was timed to coincide with the Broadway opening of "Copenhagen," an award-winning drama by British playwright Michael Frayn that won the prestigious Evening Standard Award for Best Play in 1998. The play is inspired by actual events that have intrigued and baffled historians for more than 50 years - a 1941 meeting between Bohr and Heisenberg, both brilliant physicists and longtime friends whose work together had paved the way for the atom, but who were now on opposite sides of World War II. Heisenberg, then chief scientist on the German atom-bomb project, made a covert journey at great personal risk to see his former Danish mentor and his wife Margrethe in Copenhagen, but the meeting ended in acrimony. Nothing is known of why Heisenberg made the visit, or what the two men said to each other, yet it remains a defining moment of the modern nuclear age.

Frayn's play extends the concept of quantum uncertainty to the realm of human motivations through a series of cyclic re-tellings of the same event from differing perspectives, and in Blakemore's staging the actors move about the stage as if they are particles in a quantum system. Michael Cumpsty, the actor who plays Heisenberg in the Broadway play, was on hand for the symposium, along with actress Blair Brown, who plays Margrethe Bohr. A sold-out evening session featured a panel discussion with Frayn and the play's Broadway director, Michael Blakemore.

The first session on science offered a technical exploration presenting the basics of quantum mechanics and of the contributions of Bohr, Heisenberg and others. Speakers discussed specifics of the Copenhagen Interpretation of quantum mechanics and of present views of how the wave function yields definite states. They included former APS president Eugen Merzbacher, Faye Ajzenberg-Selove of the University of Pennsylvania, Anton Zeilinger (University of Vienna), and Brian Greene, a physicist at Columbia University and author of The Elegant Universe, a discussion of superstring theory geared for a general audience. Speakers at the second session offered broad-based analyses of the scientific and historical events of the era in which the play takes place, including the reasons why the Germans did not achieve the atomic bomb, and included David Cassidy, author of the seminal Heisenberg biography, Uncertainty.

Perhaps the most poignant presentations were made by Hans Bethe and John Wheeler, both eminent physicists who themselves worked on the Allied bomb project and knew both Bohr and Heisenberg personally. Bethe declared that "Heisenberg had no interest in atomic bombs," citing as evidence the famous "Farm Hall" tapes: secretly recorded conversations of Heisenberg and the other German atomic scientists while in British custody after the war. News of the Hiroshima bombing was a great shock to the Germans who, while not very far along in the development of a genuine atomic bomb, had nevertheless felt they had gone further than the Allies. Bethe also said that Heisenberg had told him his main intention for remaining in Germany had been to save a few young physicists from going to war by employing them in the uranium project, adding, "I believe that motive."

Heisenberg's initial attempt to account for the Allied success in an impromptu tutorial for his colleagues seems to indicate that he was very far from understanding how a bomb would work, although Bethe believes such scientific mistakes demonstrate that Heisenberg was not primarily interested in building a bomb, rather than merely incompetent, as less charitable sources have maintained. Wheeler spoke of several meetings with Heisenberg, including one at the University of Michigan in 1939 from which Heisenberg left early in order to return to Germany for military training. Not surprisingly, the reception of Heisenberg among physicists in the postwar years was often chilly, he reported.

As the play makes clear, and speakers confirmed, Heisenberg tried in later years to defend his honor, and on several occasions hazarded to explain the purpose of his 1941 visit. In one such explanation, he maintained that he had come to Bohr to suggest that an atomic bomb would be too unmanageable to produce, that the German effort would not succeed, and that (by implication) the Allies should also give up the attempt. On this crucial point, historian Gerald Holton referred to a recently discovered letter written by Bohr to Heisenberg, but never posted. Holton has read the letter but it is otherwise sealed for another 12 years at the request of the Bohr estate. Without revealing the exact contents of the letter, Holton hinted that Bohr (in the unsent letter) took exception to what Heisenberg had been saying in public about their 1941 meeting.

A highlight of the day's events was the evening discussion by Frayn and Blakemore about the process of creating the play. Frayn's research included reading Heisenberg's original 1927 paper on uncertainty, and although he has no formal training in science, he says he was impressed by the clarity of the paper. He was particularly struck by the concept of irreducible quantum fuzziness which makes it impossible to know simultaneously both a particle's position and its momentum, which he extrapolated to form the thematic underpinning of his play. "Human intentions have their own irreducible fuzziness," he said. Frayn also weighed in with his own views on Heisenberg's motives for the 1941 visit; specifically, he believes the physicist had at least some intention of alerting Bohr of the unlikelihood that Germany would succeed in building a bomb. The ambiguity, he says, resulted from the need for Heisenberg to be extremely guarded in his words to avoid arrest for treason.

According to Blakemore, the staging of "Copenhagen" is similar to a scientific experiment in uncertainty, and in fact, the act of attending such a performance supports many of the play's propositions. He compared the actors to busy particles, circling around the nucleus during rehearsals until they feel ready to be seen. The audience acts as photons, shining the light of their attention onto the actors, and something that has been rehearsed a hundred times is magically altered by the impact. "The energy an audience brings to (the performance), the energy of their laughter, and rapt attention, changes what is there," he said. "Throughout 'Copenhagen,' it was extraordinary the way the act of theatergoing supports the various concepts in the play."

Philip F. Schewe of AIP's Public Information Division contributed to this coverage of the "Creating Copenhagen" symposium.