Michael Frayn - Copenhagen

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 … 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 beautiful 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 the 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 Zürich — 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 mathematics.

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 the 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 skiing 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.