Copenhagen - Michael Frayn [28]
Bohr And you didn’t?
Heisenberg I didn’t.
Bohr And that’s why you were so confident you couldn’t do it until you had the plutonium. Because you spent the entire war believing that it would take not a few kilograms of 235, but a ton or more. And to make a ton of 235 in any plausible time …
Heisenberg Would have needed something like two hundred million separator units. It was plainly unimaginable.
Bohr If you’d realised you had to produce only a few kilograms …
Heisenberg Even to make a single kilogram would need something like two hundred thousand units.
Bohr But two hundred million is one thing; two hundred thousand is another. You might just possibly have imagined setting up two hundred thousand.
Heisenberg Just possibly.
Bohr The Americans did imagine it.
Heisenberg Because Otto Frisch and Rudolf Peierls actually did the calculation. They solved the diffusion equation.
Bohr Frisch was my old assistant.
Heisenberg Peierls was my old pupil.
Bohr An Austrian and a German.
Heisenberg So they should have been making their calculation for us, at the Kaiser Wilhelm Institute in Berlin. But instead they made it at the University of Birmingham, in England.
Margrethe Because they were Jews.
Heisenberg There’s something almost mathematically elegant about that.
Bohr They also started with Perrin and Flügge.
Heisenberg They also thought it would take tons. They also thought it was unimaginable.
Bohr Until one day …
Heisenberg They did the calculation.
Bohr They discovered just how fast the chain reaction would go.
Heisenberg And therefore how little material you’d need.
Bohr They said slightly over half a kilogram.
Heisenberg About the size of a tennis ball.
Bohr They were wrong, of course.
Heisenberg They were a hundred times under.
Bohr Which made it seem a hundred times more imaginable than it actually was.
Heisenberg Whereas I left it seeming twenty times less imaginable.
Bohr So all your agonising in Copenhagen about plutonium was beside the point. You could have done it without ever building the reactor. You could have done it with 235 all the time.
Heisenberg Almost certainly not.
Bohr Just possibly, though.
Heisenberg Just possibly.
Bohr And that question you’d settled long before you arrived in Copenhagen. Simply by failing to try the diffusion equation.
Heisenberg Such a tiny failure.
Bohr But the consequences went branching out over the years, doubling and redoubling.
Heisenberg Until they were large enough to save a city. Which city? Any of the cities that we never dropped our bomb on.
Bohr London, presumably, if you’d had it in time. If the Americans had already entered the war, and the Allies had begun to liberate Europe, then …
Heisenberg Who knows? Paris as well. Amsterdam. Perhaps Copenhagen.
Bohr So, Heisenberg, tell us this one simple thing: why didn’t you do the calculation?
Heisenberg The question is why Frisch and Peierls did do it. It was a stupid waste of time. However much 235 it turned out to be, it was obviously going to be more than anyone could imagine producing.
Bohr Except that it wasn’t!
Heisenberg Except that it wasn’t.
Bohr So why …?
Heisenberg I don’t know! I don’t know why I didn’t do it! Because I never thought of it! Because it didn’t occur to me! Because I assumed it wasn’t worth doing!
Bohr Assumed? Assumed? You never assumed things! That’s how you got uncertainty, because you rejected our assumptions! You calculated, Heisenberg! You calculated everything! The first thing you did with a problem was the mathematics!
Heisenberg You should have been there to slow me down.
Bohr Yes, you wouldn’t have got away with it if I’d been standing over you.
Heisenberg Though in fact you made exactly the same assumption! You thought there was no danger for exactly the same reason as I did! Why didn’t you calculate it?
Bohr Why didn’t I calculate it?
Heisenberg Tell us why you didn’t calculate it and we’ll know why I didn’t!
Bohr It’s obvious why I didn’t!
Heisenberg Go on.
Margrethe Because he wasn’t trying to build a bomb!
Heisenberg Yes. Thank