《哥本哈根》英文剧本：第二幕

Copenhagen
by
Michael Frayn
Act Two

Heisenberg It was the very beginning of spring. The first time I came to Copenhagen, in 1924. March: raw, blustery northern weather. But every now and then the sun would come out and leave that first marvellous warmth of the year on your skin. That first breath of returning life.

Bohr You were twenty-two. So I must have been...Thirty-eight.

Bohr Almost the same age as you were when you came in 1941.

Heisenberg So what do we do?

Bohr Put on our boots and rucksacks.

Heisenberg Take the tram to the end of the line

Bohr And start walking!

Heisenberg Northwards to Elsinore.

Bohr If you walk you talk.

Heisenberg Then westwards to Tisvilde.

Bohr And back by way of Hillered.

Heisenberg Walking, talking, for a hundred miles.

Bohr After which we talked more or less non-stop for the next three years.

Heisenberg We'd split a bottle of wine over dinner in your flat at the Institute.

Bohr Then I'd come up to your room.

Heisenberg That terrible little room in the servants' quarters in the attic.

Bohr And we'd talk on into the small hours.

Heisenberg How, though?

Bohr How?

Heisenberg How did we talk? In Danish?

Bohr In German, surely.

Heisenberg I lectured in Danish. I had to give my first colloquium when I'd only been here for ten weeks.

Bohr I remember it. Your Danish was already excellent.

Heisenberg No. You did a terrible thing to me. Half-an-hour before it started you said casually, Oh, I think we'll speak English today.

Bohr But when you explained. . . ?

Heisenberg Explain to the Pope? I didn't dare. That excellent Danish you heard was my first attempt at English.

Bohr My dear Heisenberg! On our own together, though? My love, do you recall?

Margrethe What language you spoke when I wasn't there? You think I had microphones hidden?

Bohr No, no - but patience, my love, patience!

Margrethe Patience?

Bohr You sounded a little sharp.

Margrethe Not at all.

Bohr We have to follow the threads right back to the beginning of the maze.

Margrethe I'm watching every step.

Bohr You didn't mind? I hope.

Margrethe Mind?

Bohr Being left at home?

Margrethe While you went off on your hike? Of course not. Why should I have minded? You had to get out of the house. Two new sons arriving on top of each other would be rather a lot for any man to put up with.

Bohr Two new sons?

Margrethe Heisenberg.

Bohr Yes, yes.

Margrethe And our own son.

Bohr Aage?

Margrethe Ernest!

Bohr 1924 - of course - Ernest.

Margrethe Number five. Yes?

Bohr Yes, yes, yes. And if it was March, you're right - he couldn't have been much more than. ..

Margrethe One week.

Bohr One week? One week, yes. And you really didn't mind?

Margrethe Not at all. I was pleased you had an excuse to get away. And you always went off hiking with your new assistants. You went off with Kramers, when he arrived in 1916.

Bohr Yes, when I suppose Christian was still only. . .

Margrethe One week.

Bohr Yes.... Yes.... I almost killed Kramers, you know.

Heisenberg Not with a cap-pistol?

Bohr With a mine. On our walk.

Heisenberg Oh, the mine. Yes, you told me, on ours. Never mind Kramers - you almost killed yourself!

Bohr A mine washed up in the shallows. . .

Heisenberg And of course at once they compete to throw stones at it. What were you thinking of?

Bohr I've no idea.

Heisenberg A touch of Elsinore there, perhaps.

Bohr Elsinore?

Heisenberg The darkness inside the human soul.

Bohr You did something just as idiotic.

Heisenberg I did?

Bohr With Dirac in Japan. You climbed a pagoda.

Heisenberg Oh, the pagoda.

Bohr Then balanced on the pinnacle. According to Dirac. On one foot. In a high wind. I'm glad I wasn't there.

Heisenberg Elsinore, I confess.

Bohr Elsinore, certainly.

Heisenberg I was jealous of Kramers, you know.

Bohr His Eminence. Isn't that what you called him?

Heisenberg Because that's what he was. Your leading cardinal. Your favourite son. Till I arrived on the scene.

Margrethe He was a wonderful cellist.

Bohr He was a wonderful everything.

Heisenberg Far too wonderful.

Margrethe I liked him.

Heisenberg I was terrified of him. When I first started at the Institute. I was terrified of all of them. All the boy wonders you had here - they were all so brilliant and accomplished. But Kramers was the heir apparent. All the rest of us had to work in the general study hall. Kramers had the private office next to yours, like the electron on the inmost orbit around the nucleus. And he didn't think much of my physics. He insisted you could explain everything about the atom by classical mechanics.

Bohr Well, he was wrong.

Margrethe And very soon the private office was vacant.

Bohr And there was another electron on the inmost orbit.

Heisenberg Yes, and for three years we lived inside the atom.

Bohr With other electrons on the outer orbits around us all over Europe.

Heisenberg Mostly Germans.

Bohr Yes, but Schrödinger in Zurich, Fermi in Rome.

Heisenberg Chadwick and Dirac in England.

Bohr Joliot and de Broglie in Paris.

Heisenberg Gamow and Landers in Russia.

Bohr Everyone in and out of each other's departments.

Heisenberg Papers and drafts of papers on every international mail-train.

Bohr You remember when Goudsmit and Uhlenbeck did spin?

Heisenberg There's this one last variable in the quantum state of the atom that no one can make sense of. The last hurdle...

Bohr And these two crazy Dutchmen go back to a ridiculous idea that electrons can spin in different ways.

Heisenberg And of course the first thing that everyone wants to know is, What line is Copenhagen going to take?

Bohr I'm on my way to Leiden, as it happens.

Heisenberg And it turns into a papal progress! The train stops on the way at Hamburg

Bohr Pauli and Stern are waiting on the platform to ask me what I think about spin.

Heisenberg You tell them it's wrong.

Bohr No, I tell them it's very...

Heisenberg Interesting.

Bohr I think that is precisely the word I choose.

Heisenberg Then the train pulls into Leiden.

Bohr And I'm met at the barrier by Einstein and Ehrenfest. And I change my mind because Einstein - Einstein, you see? - I'm the Pope - he's God - because Einstein has made a relativistic analysis, and it resolves all my doubts.

Heisenberg Meanwhile I'm standing in for Born at Göttingen, so you make a detour there on your way home.

Bohr And you and Jordan meet me at the station.

Heisenberg Same question: what do you think of spin?

Bohr And when the train stops at Berlin there's Pauli on the platform.

Heisenberg Wolfgang Pauli, who never gets out of bed if he can possibly avoid it. . .

Bohr And who's already met me once at Hamburg on the journey out. . .

Heisenberg He's travelled all the way from Hamburg to Berlin purely in order to see you for the second time round . . .

Bohr And find out how my ideas on spin have developed en route.

Heisenberg Oh, those years! Those amazing years! Those three short years!

Bohr From 1924 to 1927.

Heisenberg From when I arrived in Copenhagen to become your assistant

Bohr To when you departed, to take up your chair at Leipzig.

Heisenberg Three years of raw, bracing northern springtime.

Bohr At the end of which we had quantum mechanics, we had uncertainty...

Heisenberg We had complementarity...

Bohr We had the whole Copenhagen Interpretation.

Heisenberg Europe in all its glory again. A new Enlightenment, with Germany back in her rightful place at the heart of it. And who led the way for everyone else?

Margrethe You and Niels.

Heisenberg Well, we did.

Bohr We did.

Margrethe And that's what you were trying to get back to in 1941?

Heisenberg To something we did in those three years...Something we said, something we thought...I keep almost seeing it out of the corner of my eye as we talk! Something about the way we worked. Something about the way we did all those things. . .

Bohr Together.

Heisenberg Together. Yes, together.

Margrethe No.

Bohr No? What do you mean, no?

Margrethe Not together. You didn't do any of those things together.

Bohr Yes, we did. Of course we did.

Margrethe No, you didn't. Every single one of them you did when you were apart. You first worked out quantum mechanics on Heligoland. You said you couldn't think in Copenhagen.

Heisenberg No, well, it was summer by then. I had my hay fever.

Margrethe on Heligoland, on your own, on a rocky bare island in the middle of the North Sea. . .

Heisenberg My head began to clear, and I had this very sharp picture of what atomic physics ought to be like. I suddenly realised that we had to limit it to the measurements we could actually make, to what we could actually observe. We can't see the electrons inside the atom . . .

Margrethe Any more than Niels can see the thoughts in your head, or you the thoughts in Niels's.

Heisenberg All we can see are the effects that the electrons produce, on the light that they reflect.. .

Bohr But the difficulties you were trying to resolve were the ones we'd explored together, over dinner in the flat, on the beach at Tisvilde.

Heisenberg Of course. But I remember the evening when the mathematics first began to chime with the principle.

Margrethe On Heligoland.

Heisenberg On Heligoland.

Margrethe On your own.

Heisenberg It was terribly laborious - I didn't understand matrix calculus then - no one did - it was a very obscure backwater of arithmetic . . . I get so excited I keep making mistakes. But by three in the morning I've got it. I seem to be looking through the surface of atomic phenomena into a strangely beautifill interior world. A world of pure mathematical structures. I'm too excited to sleep. I go down to the southern end of the island. There's a rock jutting out into the sea that I've been longing to climb. I get up it in the half-light before the dawn, and lie on top, gazing out to sea.

Margrethe On your own.

Heisenberg On my own. And yes - I was happy.

Margrethe Happier than you were back here with us all in Copenhagen the following winter.

Heisenberg What, with all the Schrödinger nonsense?

Bohr Nonsense? Come, come. Schrödinger's wave formulation?

Margrethe Yes, suddenly everyone's turned their backs on your wonderful new matrix mechanics.

Heisenberg No one can understand it.

Margrethe And they can understand Schrödinger's wave mechanics.

Heisenberg Because they'd learnt it in school! We're going backwards to classical physics! And when I'm a little cautious about accepting it. . .

Bohr A little cautious? Not to criticise, but. . .

Margrethe . . . You described it as repulsive!

Heisenberg I said the physical implications were repulsive. Schrödinger said my mathematics were repulsive.

Bohr I seem to recall you used the word... well, I won't repeat it in mixed company.

Heisenberg In private. But by that time people had gone crazy.

Margrethe They thought you were simply jealous.

Heisenberg Someone even suggested some bizarre kind of intellectual snobbery. You got extremely excited.

Bohr On your behalf.

Heisenberg You invited Schrödinger here. . .

Bohr To have a calm debate about our differences.

Heisenberg And you fell on him like a madman. You meet him at the station - of course - and you pitch into him before he's even got his bags off the train. Then you go on at him from first thing in the morning until last thing at night.

Bohr I go on? He goes on!

Heisenberg Because you won't make dhe least concession!

Bohr Nor will he!

Heisenberg You made him ill! He had to retire to bed to get away from you!

Bohr He had a slight feverish cold.

Heisenberg Margrethe had to nurse him!

Margrethe I dosed him with tea and cake to keep his strength up.

Heisenberg Yes, while you pursued him even into the sickroom! Sat on his bed and hammered away at him!

Bohr Perfectly politely.

Heisenberg You were the Pope and the Holy Office and the Inquisition all rolled into one! And then, and then, after Schrödinger had fled back to Zurich - and this I will never forget, Bohr, this I will never let you forget - you started to take his side! You turned on me!

Bohr Because you'd gone mad by this time! You'd become fanatical! You were refusing to allow wave theory any place in quantum mechanics at all!

Heisenberg You'd completely turned your coat!

Bohr I said wave mechanics and matrix mechanics were simply alternative tools.

Heisenberg Something you're always accusing me of. 'If it works it works.' Never mind what it means.

Bohr Of course I mind what it means.

Heisenberg What it means in language. Bohr In plain language, yes.

Heisenberg What something means is what it means in madhematics.
Bohr You think that so long as the mathematics works out, the sense doesn't matter.

Heisenberg Mathematics is sense! That's what sense is!

Bohr But in the end, in the end, remember, we have to be able to explain it all to Margrethe!

Margrethe Explain it to me? You couldn't even explain it to each other! You went on arguing into the small hours every night! You both got so angry!

Bohr We also both got completely exhausted.
Margrethe It was the cloud chamber that finished you.

Bohr Yes, because if you detach an electron from an atom, and send it through a cloud chamber, you can see the track it leaves.

Heisenberg And it's a scandal. There shouldn't be a track!

Margrethe According to your quantum mechanics.

Heisenberg There isn't a track! No orbits! No tracks or trajectories! Only external effects!

Margrethe Only there the track is. I've seen it myself, as clear as the wake left by a passing ship.
Bohr It was a fascinating paradox.

Heisenberg You actually loved the paradoxes, that's your problem. You revelled in dhe contradictions.

Bohr Yes, and you've never been able to understand the suggestiveness of paradox and contradiction. That's your problem. You live and breathe paradox and contradiction, but you can no more see the beauty of them than the fish can see the beauty of the water.

Heisenberg I sometimes felt as if I was trapped in a kind of windowless hell. You don't realise how aggressive you are. Prowling up and down the room as if you're going to eat someone - and I can guess who it's going to be.
Bohr That's the way we did the physics, though.

Margrethe No. No! In the end you did it on your own again! Even you! You went off ski-ing in Norway.

Bohr I had to get away from it all!

Margrethe And you worked out complementarity in Norway, on your own.

Heisenberg The speed he skis at he had to do something to keep the blood going round. It was either physics or frostbite.

Bohr Yes, and you stayed behind in Copenhagen. ..

Heisenberg And started to think at last.

Margrethe You're a lot better off apart, you two.

Heisenberg Having him out of town was as liberating as getting away from my hay fever on Heligoland.

Margrethe I shouldn't let you sit anywhere near each other, if I were the teacher.

Heisenberg And that's when I did uncertainty. Walking round Faelled Park on my own one horrible raw February night. It's very late, and as soon as I've turned off into the park I'm completely alone in the darkness. I start to think about what you'd see, if you could train a telescope on me from the mountains of Norway. You'd see me by the street lamps on the Blegdamsvej, then nothing as I vanished into the darkness, then another glimpse of me as I passed the lamp-post in front of the bandstand. And that's what we see in the cloud chamber. Not a continuous track but a series of glimpses - a series of collisions between the passing electron and various atoms of water vapour.... Or think of you, on your great papal progress to Leiden in 1925. What did Margrethe see of that, at home here in Copenhagen? A picture postcard from Hamburg, perhaps. Then one from Leiden. One from Gottingen. One from Berlin. Because what we see in the cloud chamber are not even the collisions themselves, but the water-droplets that condense around them, as big as cities around a traveller - no, vastly bigger still, relatively - complete countries - Germany... Holland... Germany again. There is no track, there are no precise addresses; only a vague list of countries visited. I don't know why we hadn't thought of it before, except that we were too busy arguing to think at all.

Bohr You seem to have given up on all forms of discussion. By the time I get back from Norway I find you've done a draft of your uncertainty paper and you've already sent it for publication!

Margrethe And an even worse battle begins.

Bohr My dear good Heisenberg, it's not open behaviour to rush a first draft into print before we've discussed it together! It's not the way we work!

Heisenberg No, the way we work is that you hound me from first thing in the morning till last thing at night! The way we work is that you drive me mad!

Bohr Yes, because the paper contains a fundamental error.

Margrethe And here we go again.

Heisenberg No, but I show him the strangest truth about the universe that any of us has stumbled on since relativity - that you can never know everything about the whereabouts of a particle, or anything else, even Bohr now, as he prowls up and down the room in that maddening way of his, because we can't observe it without introducing some new element into the situation, an atom of water vapour for it to hit, or a piece of light - things which have an energy of their own, and which therefore have an effect on what they hit. A small one, admittedly, in the case of Bohr . . .

Bohr Yes, if you know where I am with the kind of accuracy we're talking about when we're dealing with particles, you can still measure my velocity to within - what . . .?

Heisenberg Something like a billionth of a billionth of a kilometre per second. The theoretical point remains, though, that you have no absolutely determinate situation in the world, which among other things lays waste to the idea of causality, the whole foundation of science - because if you don't know how things are today you certainly can't know how they're going to be tomorrow. I shatter the objective universe around you - and all you can say is that there's an error in the formulation!

Bohr There is!

Margrethe Tea, anyone? Cake?

Heisenberg Listen, in my paper what we're trying to locate is not a free electron off on its travels through a cloud chamber, but an electron when it's at home, moving around inside an atom...

Bohr And the uncertainty arises not, as you claim, through its indeterminate recoil when it's hit by an incoming photon. . .

Heisenberg Plain language, plain language!

Bohr This is plain language.

Heisenberg Listen...

Bohr The language of classical mechanics.

Heisenberg Listen! Copenhagen is an atom. Margrethe is its nucleus. About right, the scale? Ten thousand to one?

Bohr Yes, yes.

Heisenberg Now, Bohr's an electron. He's wandering about the city somewhere in the darkness, no one knows where. He's here, he's there, he's everywhere and nowhere. Up in Faelled Park, down at Carlsberg. Passing City Hall, out by the harbour. I'm a photon. A quantum of light. I'm despatched into the darkness to find Bohr. And I succeed, because I manage to collide with him.... But what's happened? Look - he's been slowed down, he's been deflected! He's no longer doing exactly what he was so maddeningly doing when I walked into him!

Bohr But, Heisenberg, Heisenberg! You also have been deflected! If people can see what's happened to you, to their piece of light, then they can work out what must have happened to me! The trouble is knowing what's happened to you! Because to understand how people see you we have to treat you not just as a particle, but as a wave. I have to use not only your particle mechanics, I have to use the< Schrödinger wave function.

Heisenberg I know - I put it in a postscript to my paper.

Bohr Everyone remembers the paper - no one remembers the postscript. But the question is fundamental. Particles are things, complete in themselves. Waves are disturbances in something else.

Heisenberg I know. Complementarity. It's in the postscript.

Bohr They're either one thing or the other. They can't be both. We have to choose one way of seeing them or the other. But as soon as we do we can't know everytlung about them.

Heisenberg And off he goes into orbit again. Incidentally exemplifying another application of complementarily. Exactly where you go as you ramble around is of course completely determined by your genes and the various physical forces acting on you. But it's also completely determined by your own entirely inscrutable whims from one moment to the next. So we can't completely understand your behaviour without seeing it both ways at once, and that's impossible. Which means that your extraordinary peregrinations are not fully objective aspects of the universe. They exist only partially, through the efforts of me or Margrethe, as our minds shift endlessly back and forth between the two approaches.

Bohr You've never absolutely and totally accepted complementarity, have you?

Heisenberg Yes! Absolutely and totally! I defended it at the Como Conference in 1927! I have adhered to it ever afterwards with religious fervour! You convinced me. I humbly accepted your criticisms.

Bohr Not before you'd said some deeply wounding things.

Heisenberg Good God, at one point you literally reduced me to tears!

Bohr Forgive me, but I diagnosed them as tears of frustration and rage.

Heisenberg I was having a tantrum?

Bohr I have brought up children of my own.

Heisenberg And what about Margrethe? Was she having a tantrum? Klein told me you reduced her to tears after I'd gone, making her type out your endless redraftings of dhe complementarity paper.

Bohr I don't recall that.

Margrethe I do.

Heisenberg We had to drag Pauli out of bed in Hamburg once again to come to Copenhagen and negotiate peace.

Bohr He succeeded. We ended up with a treaty. Uncertainty and complementarity became the two central tenets of the Copenhagen Interpretation of Quantum Mechanics.

Heisenberg A political compromise, of course, like most treaties.

Bohr You see? Somewhere inside you There are still secret reservations.

Heisenberg Not at all - it works. That's what matters. It works, it works, it works!

Bohr It works, yes. But it's more important than that. Because you see what we did in those three years, Heisenberg? Not to exaggerate, but we turned the world inside out! Yes, listen, now it comes, now it comes.... We put man back at the centre of the universe. Throughout history we keep finding ourselves displaced. We keep exiling ourselves to the periphery of things. First we turn ourselves into a mere adjunct of God's unknowable purposes, tiny figures kneeling in the great cathedral of creation. And no sooner have we recovered ourselves in the Renaissance, no sooner has man become, as Protagoras proclaimed him, the measure of all things, than we're pushed aside again by the products of our own reasoning!- We're dwarfed again as physicists build the great new cathedrals for us to wonder at - the laws of classical mechanics that predate us from the beginning of eternity, that will survive us to eternity's end, that exist whether we exist or not. Until we come to the beginning of the twentieth century, and we're suddenly forced to rise from our knees again.

Heisenberg It starts with Einstein.

Bohr It starts with Einstein. He shows that measurement - measurement, on which the whole possibility of science depends - measurement is not an impersonal event that occurs with impartial universality. It's a human act, carried out from a specific point of view in time and space, from the one particular viewpoint of a possible observer. Then, here in Copenhagen in those three years in the mid twenties we discover that there is no precisely determinable objective universe. That the universe exists only-as a series of approximations. Only within the limits determined by our relationship with it. Only through the understanding lodged inside the human head

Margrethe So this man you've put at the centre of the universe - is it you, or is it Heisenberg?

Bohr Now, now, my love.

Margrethe Yes, but it makes a difference.

Bohr Either of us. Both of us. Yourself. All of us.

Margrethe If it's Heisenberg at the centre of the universe, then the one bit of the universe that he can't see is Heisenberg.

Heisenberg So...

Margrethe So it's no good asking him why he came to Copenhagen in 1941. He doesn't know!

Heisenberg I thought for a moment just then I caught a glimpse of it.

Margrethe Then you turned to look.

Heisenberg And away it went.

Margrethe Complementarity again. Yes?

Bohr Yes, yes.

Margrethe I've typed it out often enough. If you're doing something you have to concentrate on you can't also be thinking about doing it, and if you're thinking about doing it then you can't actually be doing it. Yes?

Heisenberg Swerve left, swerve right, or think about it and die.

Bohr But after you've done it. . .

Margrethe You look back and make a guess, just like the rest of us. Only a worse guess, because you didn't see yourself doing it, and we did. Forgive me, but you don't even know why you did uncertainty in the first place.

Bohr Whereas if you're the one at the centre of the universe . . .

Margrethe Then I can tell you that it was because you wanted to drop a bomb on Schrödinger.

Heisenberg I wanted to show he was wrong, certainly.

Margrethe And Schrödinger was winning the war. When the Leipzig chair first became vacant that autumn he was short-listed for it and you weren't. You needed a wonderful new weapon.

Bohr Not to criticise, Margrethe, but you have a tendency to make everything personal.

Margrethe Because everything is personal! You've just read us all a lecture about it! You know how much Heisenberg wanted a chair. You know the pressure he was under from his family. I'm sorry, but you want to make everything seem heroically abstract and logical. And when you tell the story, yes, it all falls into place, it all has a beginning and a middle and an end. But I was there, and when I remember what it was like I'm there still, and I look around me and what I see isn't a story! It's confusion and rage and jealousy and tears and no one knowing what things mean or which way they're going to go.

Heisenberg All the same, it works, it works.

Margrethe Yes, it works wonderfully. Within three months of publishing your uncertainty paper you're offered Leipzig.

Heisenberg I didn't mean that.

Margrethe Not to mention somewhere else and somewhere else.

Heisenberg Halle and Munich and Zürich.

Bohr And various American universities.

Heisenberg But I didn't mean that.

Margrethe And when you take up your chair at Leipzig you're how old?

Heisenberg Twenty-six.

Bohr The youngest full professor in Germany.

Heisenberg I mean the Copenhagen Interpretation. The Copenhagen Interpretation works. However we got there, by whatever combination of high principles and low calculation, of most painfully hard thought and most painfully childish tears, it works. It goes on working.

Margrethe Yes, and why did you both accept the Interpretation in the end? Was it really because you wanted to re-establish humanism?

Bohr Of course not. It was because it was the only way to explain what the experimenters had observed.

Margrethe Or was it because now you were becoming a professor you wanted a solidly established doctrine to teach? Because you wanted to have your new ideas publicly endorsed by the head of the church in Copenhagen? And perhaps Niels agreed to endorse them in return for your accepting his doctrines. For recognising him as head of the church. And if you want to know why you came to Copenhagen in 1941 I'll tell you that as well. You're right - there's no great mystery about it. You came to show yourself off to us.

Bohr Margrethe!

Margrethe No! When he first came in 1924 he was a humble assistant lecturer from a humiliated nation, grateful to have a job. Now here you are, back in triumph - the leading scientist in a nation that's conquered most of Europe. You've come to show us how well you've done in life.

Bohr This is so unlike you!

Margrethe I'm sorry, but isn't that really why he's here? Because he's burning to let us know that he's in charge of some vital piece of secret research. And that even so he's preserved a lofty moral independence. Preserved it so famously that he's being watched by the Gestapo. Preserved it so successfully that he's now also got a wonderfully important moral dilemma to face.

Bohr Yes, well, now you're simply working yourself up.

Margrethe A chain reaction. You tell one painful truth and it leads to two more. And as you frankly admit, you're going to go back and continue doing precisely what you were doing before, whatever Niels tells you.

Heisenberg Yes.

Margrethe Because you wouldn't dream of giving up such a wonderful opportunity for research.

Heisenberg Not if I can possibly help it.

Margrethe Also you want to demonstrate to the Nazis how useful theoretical physics can be. You want to save the honour of German science. You want to be there to re establish it in all its glory as soon as the war's over.

Heisenberg All the same, I don't tell Speer that the reactor . . .

Margrethe . . . will produce plutonium, no, because you're afraid of what will happen if the Nazis commit huge resources, and you fail to deliver the bombs. Please don't try to tell us that you're a hero of the resistance

Heisenberg I've never claimed to be a hero.

Margrethe Your talent is for ski-ing too fast for anyone to see where you are. For always being in more than one position at a time, like one of your particles.

Heisenberg I can only say that it worked. Unlike most of the gestures made by heroes of the resistance. It worked! I know what you think. You think I should have joined the plot against Hitler, and got myself hanged like the others.

Bohr Of course not.

Heisenberg You don't say it, because there are some things that can't be said. But you think it.

Bohr No.

Heisenberg What would it have achieved? What would it have achieved if you'd dived in after Christian, and drowned as well? But that's another thing that can't be said.

Bohr Only thought.

Heisenberg Yes. I'm sorry.

Bohr And rethought. Every day.

Heisenberg You had to be held back, I know.

Margrethe Whereas you held yourself back.

Heisenberg Better to stay on the boat, though, and fetch it about. Better to remain alive, and throw the lifebuoy. Surely!

Bohr Perhaps. Perhaps not.

Heisenberg Better. Better.

Margrethe Really it is ridiculous. You reasoned your way, both of you, with such astonishing delicacy and precision into the tiny world of the atom. Now it turns out that everything depends upon these really rather large objects on our shoulders. And what's going on in there is . .

Heisenberg Elsinore.

Margrethe Elsinore, yes.

Heisenberg And you may be right. I was afraid of what would happen. I was conscious of being on the winning side. .. So many explanations for everything I did! So many of them sitting round the lunch-table! Somewhere at the head of the table, I think, is the real reason I came to Copenhagen. Again I turn to look.... And for a moment I almost see its face. Then next time I look the chair at the head of the table is completely empty. There's no reason at all. I didn't tell Speer simply because I didn't think of it. I came to Copenhagen simply because I did think of it. A million things we might do or might not do every day. A million decisions that make themselves.

Bohr Why didn't I . . . ?

Heisenberg Kill me. Murder me. That evening in 1941. Here we are, walking back towards the house, and you've just leapt to the conclusion that I'm going to arm Hitler with nuclear weapons. You'll surely take any reasonable steps to prevent