Copenhagen

by Michael Frayn

  Bohr My dear Heisenberg!

  Heisenberg My dear Bohr!

  Bohr Come in, come in …

  Heisenberg How difficult it is to see even what’s in front of one’s eyes. All we possess is the present, and the present endlessly dissolves into the past. Bohr has gone even as I turn to see Margrethe.

  Margrethe Niels is right. You look older.

  Bohr I believe you had some personal trouble.

  Heisenberg Margrethe slips into history even as I turn back to Bohr. And yet how much more difficult still it is to catch the slightest glimpse of what’s behind one’s eyes. Here I am at the centre of the universe, and yet all I can see are two smiles that don’t belong to me.

  Margrethe How is Elisabeth? How are the children?

  Heisenberg Very well. They send their love, of course … I can feel a third smile in the room, very close to me. Could it be the one I suddenly see for a moment in the mirror there? And is the awkward stranger wearing it in any way connected with this presence that I can feel in the room? This all-enveloping, unobserved presence?

  Margrethe I watch the two smiles in the room, one awkward and ingratiating, the other rapidly fading from incautious warmth to bare politeness. There’s also a third smile in the room, I know, unchangingly courteous, I hope, and unchangingly guarded.

  Heisenberg You’ve managed to get some skiing?

  Bohr I glance at Margrethe, and for a moment I see what she can see and I can’t—myself, and the smile vanishing from my face as poor Heisenberg blunders on.

  Heisenberg I look at the two of them looking at me, and for a moment I see the third person in the room as clearly as I see them. Their importunate guest, stumbling from one crass and unwelcome thoughtfulness to the next.

  Bohr I look at him looking at me, anxiously, pleadingly, urging me back to the old days, and I see what he sees. And yes—now it comes, now it comes—there’s someone missing from the room. He sees me. He sees Margrethe. He doesn’t see himself.

  Heisenberg Two thousand million people in the world, and the one who has to decide their fate is the only one who’s always hidden from me.

  Bohr You suggested a stroll.

  Heisenberg You remember Elsinore? The darkness inside the human soul …?

  Bohr And out we go. Out under the autumn trees. Through the blacked-out streets.

  Heisenberg Now there’s no one in the world except Bohr and the invisible other. Who is he, this all-enveloping presence in the darkness?

  Margrethe The flying particle wanders the darkness, no one knows where. It’s here, it’s there, it’s everywhere and nowhere.

  Bohr With careful casualness he begins to ask the question he’s prepared.

  Heisenberg Does one as a physicist have the moral right to work on the practical exploitation of atomic energy?

  Margrethe The great collision.

  Bohr I stop. He stops …

  Margrethe This is how they work.

  Heisenberg He gazes at me, horrified.

  Margrethe Now at last he knows where he is and what he’s doing.

  Heisenberg He turns away.

  Margrethe And even as the moment of collision begins it’s over.

  Bohr Already we’re hurrying back towards the house.

  Margrethe Already they’re both flying away from each other into the darkness again.

  Heisenberg Our conversation’s over.

  Bohr Our great partnership.

  Heisenberg All our friendship.

  Margrethe And everything about him becomes as uncertain as it was before.

  Bohr Unless … yes … a thought-experiment .… Let’s suppose for a moment that I don’t go flying off into the night. Let’s see what happens if instead I remember the paternal role I’m supposed to play. If I stop, and control my anger, and turn to him. And ask him why.

  Heisenberg Why?

  Bohr Why are you confident that it’s going to be so reassuringly difficult to build a bomb with 235? Is it because you’ve done the calculation?

  Heisenberg The calculation?

  Bohr Of the diffusion in 235. No. It’s because you haven’t calculated it. You haven’t considered calculating it. You hadn’t consciously realised there was a calculation to be made.

  Heisenberg And of course now I have realised. In fact it wouldn’t be all that difficult. Let’s see .… The scattering cross-section’s about 6 × 10−24, so the mean free path would be … Hold on …

  Bohr And suddenly a very different and very terrible new world begins to take shape …

  Margrethe That was the last and greatest demand that Heisenberg made on his friendship with you. To be understood when he couldn’t understand himself. And that was the last and greatest act of friendship for Heisenberg that you performed in return. To leave him misunderstood.

  Heisenberg Yes. Perhaps I should thank you.

  Bohr Perhaps you should.

  Margrethe Anyway, it was the end of the story.

  Bohr Though perhaps there was also something I should thank you for. That summer night in 1943, when I escaped across the Sound in the fishing-boat, and the freighters arrived from Germany …

  Margrethe What’s that to do with Heisenberg?

  Bohr When the ships arrived on the Wednesday there were eight thousand Jews in Denmark to be arrested and crammed into their holds. On the Friday evening, at the start of the Sabbath, when the SS began their round-up, there was scarcely a Jew to be found.

  Margrethe They’d all been hidden in churches and hospitals, in people’s homes and country cottages.

  Bohr But how was that possible?—Because we’d been tipped off by someone in the German Embassy.

  Heisenberg Georg Duckwitz, their shipping specialist.

  Bohr Your man?

  Heisenberg One of them.

  Bohr He was a remarkable informant. He told us the day before the freighters arrived—the very day that Hitler issued the order. He gave us the exact time that the SS would move.

  Margrethe It was the Resistance who got them out of their hiding-places and smuggled them across the Sound.

  Bohr For a handful of us in one fishing smack to get past the German patrol-boats was remarkable enough. For a whole armada to get past, with the best part of eight thousand people on board, was like the Red Sea parting.

  Margrethe I thought there were no German patrol-boats that night?

  Bohr No—the whole squadron had suddenly been reported unseaworthy.

  Heisenberg How they got away with it I can’t imagine.

  Bohr Duckwitz again?

  Heisenberg He also went to Stockholm and asked the Swedish Government to accept everyone.

  Bohr So perhaps I should thank you.

  Heisenberg For what?

  Bohr My life. All our lives.

  Heisenberg Nothing to do with me by that time. I regret to say.

  Bohr But after I’d gone you came back to Copenhagen.

  Heisenberg To make sure that our people didn’t take over the Institute in your absence.

  Bohr I’ve never thanked you for that, either.

  Heisenberg You know they offered me your cyclotron?

  Bohr You could have separated a little 235 with it.

  Heisenberg Meanwhile you were going on from Sweden to Los Alamos.

  Bohr To play my small but helpful part in the deaths of a hundred thousand people.

  Margrethe Niels, you did nothing wrong!

  Bohr Didn’t I?

  Heisenberg Of course not. You were a good man, from first to last, and no one could ever say otherwise. Whereas I …

  Bohr Whereas you, my dear Heisenberg, never managed to contribute to the death of one single solitary person in all your life.

  Margrethe Well, yes.

  Heisenberg Did I?

  Margrethe One. Or so you told us. The poor fellow you guarded overnight, when you were a boy in Munich, while he was waiting to be shot in the morning.

  Bohr All right then, one. One single soul on his conscience, to set
against all the others.

  Margrethe But that one single soul was emperor of the universe, no less than each of us. Until the morning came.

  Heisenberg No, when the morning came I persuaded them to let him go.

  Bohr Heisenberg, I have to say—if people are to be measured strictly in terms of observable quantities …

  Heisenberg Then we should need a strange new quantum ethics. There’d be a place in heaven for me. And another one for the SS man I met on my way home from Haigerloch. That was the end of my war. The Allied troops were closing in; there was nothing more we could do. Elisabeth and the children had taken refuge in a village in Bavaria, so I went to see them before I was captured. I had to go by bicycle—there were no trains or road transport by that time—and I had to travel by night and sleep under a hedge by day, because all through the daylight hours the skies were full of Allied planes, scouring the roads for anything that moved. A man on a bicycle would have been the biggest target left in Germany. Three days and three nights I travelled. Out of Württemberg, down through the Swabian Jura and the first foothills of the Alps. Across my ruined homeland. Was this what I’d chosen for it? This endless rubble? This perpetual smoke in the sky? These hungry faces? Was this my doing? And all the desperate people on the roads. The most desperate of all were the SS. Bands of fanatics with nothing left to lose, roaming around shooting deserters out of hand, hanging them from roadside trees. The second night, and suddenly there it is—the terrible familiar black tunic emerging from the twilight in front of me. On his lips as I stop—the one terrible familiar word. ‘Deserter,’ he says. He sounds as exhausted as I am. I give him the travel order I’ve written for myself. But there’s hardly enough light in the sky to read by, and he’s too weary to bother. He begins to open his holster instead. He’s going to shoot me because it’s simply less labour. And suddenly I’m thinking very quickly and clearly—it’s like skiing, or that night on Heligoland, or the one in Faelled Park. What comes into my mind this time is the pack of American cigarettes I’ve got in my pocket. And already it’s in my hand—I’m holding it out to him. The most desperate solution to a problem yet. I wait while he stands there looking at it, trying to make it out, trying to think, his left hand holding my useless piece of paper, his right on the fastening of the holster. There are two simple words in large print on the pack: Lucky Strike. He closes the holster, and takes the cigarettes instead .… It had worked, it had worked! Like all the other solutions to all the other problems. For twenty cigarettes he let me live. And on I went. Three days and three nights. Past the weeping children, the lost and hungry children, drafted to fight, then abandoned by their commanders. Past the starving slave-labourers walking home to France, to Poland, to Estonia. Through Gammertingen and Biberach and Memmingen. Mindelheim, Kaufbeuren, and Schöngau. Across my beloved homeland. My ruined and dishonoured and beloved homeland.

  Bohr My dear Heisenberg! My dear friend!

  Margrethe Silence. The silence we always in the end return to.

  Heisenberg And of course I know what they’re thinking about.

  Margrethe All those lost children on the road.

  Bohr Heisenberg wandering the world like a lost child himself.

  Margrethe Our own lost children.

  Heisenberg And over goes the tiller once again.

  Bohr So near, so near! So slight a thing!

  Margrethe He stands in the doorway, watching me, then he turns his head away …

  Heisenberg And once again away he goes, into the dark waters.

  Bohr Before we can lay our hands on anything, our life’s over.

  Heisenberg Before we can glimpse who or what we are, we’re gone and laid to dust.

  Bohr Settled among all the dust we raised.

  Margrethe And sooner or later there will come a time when all our children are laid to dust, and all our children’s children.

  Bohr When no more decisions, great or small, are ever made again. When there’s no more uncertainty, because there’s no more knowledge.

  Margrethe And when all our eyes are closed, when even the ghosts have gone, what will be left of our beloved world? Our ruined and dishonoured and beloved world?

  Heisenberg But in the meanwhile, in this most precious meanwhile, there it is. The trees in Faelled Park. Gammertingen and Biberach and Mindelheim. Our children and our children’s children. Preserved, just possibly, by that one short moment in Copenhagen. By some event that will never quite be located or defined. By that final core of uncertainty at the heart of things.

  POSTSCRIPT

  Where a work of fiction features historical characters and historical events it’s reasonable to want to know how much of it is fiction and how much of it is history. So let me make it as clear as I can in regard to this play.

  The central event in it is a real one. Heisenberg did go to Copenhagen in 1941, and there was a meeting with Bohr, in the teeth of all the difficulties encountered by my characters. He almost certainly went to dinner at the Bohrs’ house, and the two men almost certainly went for a walk to escape from any possible microphones, though there is some dispute about even these simple matters. The question of what they actually said to each other has been even more disputed, and where there’s ambiguity in the play about what happened, it’s because there is in the recollection of the participants. Much more sustained speculation still has been devoted to the question of what Heisenberg was hoping to achieve by the meeting. All the alternative and co-existing explications offered in the play, except perhaps the final one, have been aired at various times, in one form or another.

  Most anxious of all to establish some agreed version of the meeting was Heisenberg himself. He did indeed go back in 1947 with his British minder, Ronald Fraser, and attempted to find some common ground in the matter with Bohr. But it proved to be too delicate a task, and (according to Heisenberg, at any rate, in his memoirs) ‘we both came to feel that it would be better to stop disturbing the spirits of the past.’ This is where my play departs from the historical record, by supposing that at some later time, when everyone involved had become spirits of the past themselves, they argued the question out further, until they had achieved a little more understanding of what was going on, just as they had so many times when they were alive with the intractable difficulties presented by the internal workings of the atom.

  The account of these earlier discussions in the twenties reflects at any rate one or two of the key topics, and the passion with which the argument was conducted, as it emerges from the biographical and autobiographical record. I am acutely aware of how over-simplified my version is. Max Born described the real story as not so much ‘a straight staircase upwards, but a tangle of interconnected alleys,’ and I have found it impossible to follow these in any detail (even where I can begin to understand them). In particular I have grossly understated the crucial role played by Born himself and by his pupil Pascual Jordan at Göttingen in formulating quantum mechanics (it was Born who supplied the understanding of matrices that Heisenberg lacked, and the statistical interpretation of Schrödinger’s wave function), and of Wolfgang Pauli in Hamburg, whose exclusion principle filled in one of the key pieces in the puzzle.

  But the account of the German and American bomb programmes, and of the two physicists’ participation in them, is taken from the historical record; so is the fate of Danish Jewry; Heisenberg’s experiences in Germany before and during the war, his subsequent internment, and the depression that clouded his later years. I have filled out some of the details, but in general what he says happened to him—at the end of the First World War, on Heligoland, during his nocturnal walk in Faelled Park, during the Berlin air-raid and his internment, and on his ride across Germany, with its near-fatal encounter along the way—is based very closely upon the accounts he gave in life.

  The actual words spoken by my characters are of course entirely their own. If this needs any justification then I can only appeal to Heisenberg himself. In his memoirs dialogue plays an importa
nt part, he says, because he hopes ‘to demonstrate that science is rooted in conversations.’ But, as he explains, conversations, even real conversations, cannot be reconstructed literally several decades later. So he freely reinvents them, and appeals in his turn to Thucydides. (Heisenberg’s father was a professor of classics, and he was an accomplished classicist himself, on top of all his other distinctions.) Thucydides explains in his preface to the History of the Peloponnesian War that, although he had avoided all ‘storytelling’, when it came to the speeches, ‘I have found it impossible to remember their exact wording. Hence I have made each orator speak as, in my opinion, he would have done in the circumstances, but keeping as close as I could to the train of thought that guided his actual speech.’ Thucydides was trying to give an account of speeches that had actually been made, many of which he had himself heard. Some of the dialogue in my play represents speeches that must have been made in one form or another; some of it speeches that were certainly never made at all. I hope, though, that in some sense it respects the Thucydidean principle, and that speeches (and indeed actions) follow in so far as possible the original protagonists’ train of thought.

  But how far is it possible to know what their train of thought was? This is where I have departed from the established historical record—from any possible historical record. The great challenge facing the storyteller and the historian alike is to get inside people’s heads, to stand where they stood and see the world as they saw it, to make some informed estimate of their motives and intentions—and this is precisely where recorded and recordable history cannot reach. Even when all the external evidence has been mastered, the only way into the protagonists’ heads is through the imagination. This indeed is the substance of the play.

  *

  I can’t claim to be the first person to notice the parallels between Heisenberg’s science and his life. They provide David Cassidy with the tide (Uncertainty) for his excellent biography (the standard work in English). ‘Especially difficult and controversial,’ says Cassidy in his introduction, ‘is a retrospective evaluation of Heisenberg’s activities during the Third Reich and particularly during World War II. Since the end of the war, an enormous range of views about this man and his behaviour have been expressed, views that have been fervently, even passionately, held by a variety of individuals. It is as if, for some, the intense emotions unleashed by the unspeakable horrors of that war and regime have combined with the many ambiguities, dualities, and compromises of Heisenberg’s life and actions to make Heisenberg himself subject to a type of uncertainty principle …’ Thomas Powers makes a similar point in his extraordinary and encyclopaedic book Heisenberg’s War, which first aroused my interest in the trip to Copenhagen; he says that Heisenberg’s later reticence on his role in the failure of the German bomb programme ‘introduces an element of irreducible uncertainty.’