• Michael Frayn's dazzling play about quantum physics, moral responsibility, and the uncertainties of human motivation. Copenhagen focuses on one of the most mysterious incidents in modern scientific history: the clandestine visit that Werner Heisenberg, the German physicist charged with developing an atom bomb for the Nazis, paid to his former mentor, the half-Jewish Niels Bohr, in occupied Denmark in 1941. Over the years, many reasons have been suggested for this inconclusive visit: did Heisenberg mean to warn Bohr about the Nazis' atomic weapons programme, recruit him to it, or fish for information about developments on the Allied side? In Frayn's play Bohr and Heisenberg re-enact several possible versions of the meeting in what appears to be some kind of post-death limbo. The presence of a third character, Bohr's wife Margrethe, ensures that the technical points of their discussionare explained in terms that are just about intelligible to a lay audience. Gradually, the conceptsof 'uncertainty' and 'complementarity' devised by the two men in their work on quantumtheory emerge as radical metaphors for human experience.

    Copenhagen was first staged at the National Theatre's intimate Cottesloe Theatre in 1998, in a starkly effective production by Michael Blakemore: Heisenberg was played by Matthew Marsh, Bohr by David Burke, and Margrethe by Sara Kestleman. Perhaps surprisingly for a play on such an abstruse topic, it played to full houses for eight months before transferring to the West End, where it ran for another two years. Copenhagen enjoyed a comparable triumph on Broadway, where it won the Tony Awards for Best Play and Best director.

    The play has a curious (if oddly fitting) sequel. While Copenhagen was still running at the National, Frayn received a parcel of yellowing papers from a woman named Celia Pryce-Jones. These had supposedly been found at the house in which Heisenberg was interned at the end of the war and seemed to shed new light on his actions and motives. Hugely excited, Frayn threw himself into months of speculation and research only to discover, eventually, that he had been duped. The documents were an elaborate practical joke by David Burke, the actor who played Bohr in the original production. Burke and Frayn later collaborated on a book about the deception, Celia's Secret.