Uncertainty of truth and memory

MICHELE HEWITSON explores the mysteries of a play about a crucial argument between two nuclear physicists whose positions cannot be determined.

Sometimes history can be made by something which never happened. That is one of the conundrums at the heart of Copenhagen, the theatrical intellectual thriller by Michael Frayn which opens at the Herald Theatre on Wednesday.

At the core of that which never happened - Germany's ability to develop and use an atomic bomb before the end of the Second World War - is a mysterious visit.

On a September day in 1941 the German physicist Werner Heisenberg visited his great friend, the Danish physicist Niels Bohr, in German-occupied Copenhagen. They had been friends for years, had an intimate working relationship and the measured Bohr (played by Stuart Devenie) was father-figure to the impetuous Heisenberg. The mystery was not that they argued: they had fought before, and fiercely, on matters of physics.

On this occasion, however, they had a terrible row, a conversation which went wildly astray.

There is no great mystery attached to the fact that great friends can, and do, fall out irreparably. And for all their intimacy, they approached the subject at the heart of their relationship (they are together in the reference books as the inventors of modern quantum physics) quite differently.

Bohr's wife, Margrethe (played by Ilona Rodgers), is known to have been cool on the topic of Heisenberg (David Aston), who approached science in the same way that he approached life.

In Frayn's play, says Elric Hooper, director of the Auckland Theatre Company season, we see Heisenberg as "a mathematical genius who wants to solve problems and will do whatever [it takes].

"The image is of skiing downhill and if you go fast enough you can leap the crevasses. But if you go as slow as Bohr, you have to go down the crevasses and look into them."

On that day in 1941 both physicists looked into a crevasse at the bottom of which lay the wreck of their friendship and their working collaboration. They did not see each other again until 1947 when Heisenberg again came to Denmark. There they attempted to work out what exactly had happened six years earlier.

They were unable to agree even on where they had the conversation. Heisenberg remembered it taking place on an evening walk. Bohr was sure it took place in his study. Heisenberg later wrote in his memoirs that they eventually agreed that it would be better to leave the ghosts of the encounter to rest. There were plenty of other interested parties who disagreed.

The conversation was analysed by intelligence authorities after the part-Jewish Bohr's flight to Sweden in 1941 and has been argued about by scientists and historians for decades afterwards. It has been the topic of books and papers. But nobody has been able to agree on what really happened.

This is what is known: Heisenberg made a risky journey to tell Bohr that Germany was involved in a research effort to develop an atomic bomb.

What is not known is why he came, or what made Bohr so furious. That is the great mystery. These questions are important because they lead to the big question: what if Hitler had had the bomb?

As Hooper points out, "Something didn't happen there. It's a non-event which this is about. It's really one of the great omissions. If something happened there the history of the world may have been changed."

Speculation on whether Heisenberg bungled the maths - and, if he did, whether he did so deliberately because of moral misgivings - will likely never end. That speculation leads to another related question: how did that conversation begin?

Frayn has Heisenberg saying to Bohr, "I simply asked you if, as a physicist, one had the moral right to work on the practical exploitation of atomic energy. Yes?" It is the question Heisenberg says he posed.

Frayn has Bohr responding that he doesn't remember. (And he appears to have left no recollection.) Frayn has Margrethe answering the question with one of her own: "You're not suggesting Niels did anything wrong working at Los Alamos?" (After his escape to Sweden, Bohr worked in the secret American laboratory.)

Frayn assembles his players, the ghosts of Bohr, Heisenberg and Margrethe, in a sort of limbo where they replay that conversation four times - without ever agreeing on what actually happened.

"It's reassuring," says Hooper, "to find that the dead are just as confused as the living." Which is the sort of observation you might expect from a director: in the afterlife you can redirect the scene for all eternity. "You have," says Hooper, "to relive the thing in order to get to some sort of truth."

That confusion, or at least the idea of eternal uncertainty, is attractive, dramatically. Frayn explores Heisenberg's "uncertainty principle", the principle that in the subatomic world you can never know both the position and velocity of a particle, as metaphor: that you can never know what is happening in people's minds. Or our motivations, when memory has added its twists.

Margrethe says of Heisenberg: "So it's no good asking him why he came to Copenhagen in 1941. He doesn't know."

Copenhagen is not about getting to the truth. The questions the story poses remain up for retelling. For now at least. There is a letter, from Bohr, written in response to Heisenberg's published version of the 1941 meeting, and found after his death. His family have embargoed its contents until 2012.