I Can See No Inconsistency

Dublin, the winter of forty-four, the war still going, and in Nature a quarrel about whether light makes up its own mind. Schrödinger reads it at his desk and takes the other side for an afternoon, the side he doesn't hold, because somebody has proved a thing too easily, and he can't stand to watch it.

Whittaker had said: give each photon a yes or a no, then turn the prism while it flies, and the yes can't follow the turn, so there is no yes. The beam, he said, cannot know at what angle the Nicol will be set. True, says the man in Dublin. It can't. It doesn't have to know. Give it a number instead of a word, anything from nothing to one, spread even as rain on a roof, and let it through whenever the number clears the sine of the angle, squared. Do the sum. Cosine squared comes out the far side, the way it should.

Then the part I like. Once they're through, the survivors aren't even any more, they're all high numbers, so he stretches what's left back over nothing-to-one, and the turned-away ones too, by a rule of their own, so both beams leave the door as mixed as they came. Whichever way you come out, the door writes you a new number. And under it, in his hand: I can see no inconsistency in assuming these changes.

That isn't belief. That's a carpenter saying the joint will hold. Then he turns the page and says what he does think: the strongest plea for chance is older than the quantum, as old as the gas in a box before the eighteen-seventies were out, that we learned the word law from crowds and then pretended every member of the crowd obeyed it. If we could stop pretending, he wrote, it would be an advantage. It would unify the picture.

Then, probably, he heard that Pelzer had said it in print, and put the pages down. Eighty years in a box in Vienna, a working machine for a world he didn't live in, correct, and finished, and sure of only the one small thing, that you don't win by forbidding the other side to build. Somebody opened the drawer this week. The joint still holds. The light goes through the second prism and the third, stretched each time back to whole, as mixed as when it set out, and not one photon of it knowing which way the glass was turned.