Two cultures? Nuclear explosions hit the stage

Next Friday, nuclear fission comes to the West End stage. The play, mainly set in 1941 Denmark, concerns a mysterious meeting between two physicists at which they discussed whether it might be possible to split uranium atoms and set off a nuclear chain reaction. A singularly unpromising subject for a theatrical spectacle, you might think.

But you'd be wrong. The leading humourist Michael Frayn took this material and fashioned it into Copenhagen, one of the biggest hits at the National Theatre last year. Frayn is still surprised by his play's success. "I've never had the slightest idea of whether any of my plays would be popular."

So why did the nuclear meeting have the ingredients of a successful drama? Well, it took place in Nazi-occupied Copenhagen between the great Danish physicist Niels Bohr and his friend Werner Heisenberg, who was working for the Germans. Both were working on nuclear fission, which had been unexpectedly discovered shortly before the outbreak of the war, and both knew that if the energy released in these reactions could be harnessed, the result would be the most devastating weapon ever seen. They knew, too, it could be catastrophic if such a weapon were in the wrong hands.

Frayn, still in command of the research he did before he wrote the play, lists some of the perplexing questions about the meeting. Why did Heisenberg ask to see his friend? Was he trying to screw information out of Bohr about the allies' plans? Or was he trying discreetly to pass on to the allies information about German progress? And why couldn't the men subsequently agree on anything about the meeting? The play addresses these and other questions through a series of invented (but plausible) scenes between the patriarchal Bohr, the competitive Heisenberg and Bohr's plain-speaking wife Margrethe, who exposes the scientists' evasions.

"We shall probably never know the answers to the questions the play addresses", Frayn says, "because the more we study the evidence, the less it becomes clear." This historical fuzziness is reminiscent of the uncertainty principle, one of the cornerstones of quantum theory, discovered by Heisenberg 14 years before the meeting. This principle gives limits to what we can know about the world and says, for example, that the more we know about where an electron is, the less we can know about its momentum. The very act of observing something unavoidably limits what we can know about it.

"Our director Michael Blakemore ingeniously draws attention to the play's theme of observation," Frayn enthuses, "by surrounding the players with the audience." Here, the audience members are the observers, the play is the apparatus and the evening is the two-hour experiment. Frayn is delighted that they have been able to transfer the play to the cosy Duchess Theatre, which enables the National production's staging to be preserved in almost every detail. The "absolutely marvellous" cast is, happily, also unchanged.

Frayn is surprised that audiences are so eager to engage with his scientific and philosophical themes. "The theatre has always relied heavily on audiences respecting conventions that we've come to take for granted. But I've been gratified and touched by the concentration of Copenhagen's audiences and by their willingness to engage with difficult ideas."

To see Copenhagen is to be part of Frayn's probing of the subtleties of nuclear physics and human motivation. The result at each performance is the most successful science-art fusion seen on the stage for years.

Graham Farmelo is Head of Exhibitions at the Science Museum, London.