“Ah, but not in this universe-”
The Librarian opened one eye.
“You suggestin' I nipped into some other universe to get married?” said Ridcully.
“No! I mean, you got married in that universe and not in this universe,” said Ponder.
“Did I? What? A proper ceremony and everything?”
“Yes!”
“Hmm.” Ridcully stroked his beard. “You sure?”
“Certain, Archchancellor.”
“My word! I never knew that.”
Ponder felt he was getting somewhere.
“So-”
“Yes?”
“Why don't I remember it?”
Ponder had been ready for this.
“Because the you in the other universe is different from the you here,” he said. “It was a different you that got married. He's probably settled down somewhere. He's probably a great-grandad by now.”
“He never writes, I know that,” said Ridcully “And the bastard never invited me to the wedding.”
“Who?”
“Him.”
“But he's you!”
“Is he? Huh! You'd think I'd think of me, wouldn't you? What a bastard!”
It wasn't that Ridcully was stupid. Truly stupid wizards have the life expectancy of a glass hammer. He had quite a powerful intellect, but it was powerful like a locomotive, and ran on rails and was therefore almost impossible to steer.
There are indeed such things as parallel universes, although parallel is hardly the right word - universes swoop and spiral around one another like some mad weaving machine or a squadron of Yossarians with middle-ear trouble.
And they branch. But, and this is important, not all the time. The universe doesn't much care if you tread on a butterfly. There are plenty more butterflies. Gods might note the fall of a sparrow but they don't make any effort to catch them.
Shoot the dictator and prevent the war? But the dictator is merely the tip of the whole festering boil of social pus from which dictators emerge; shoot one, and there'll be another one along in a minute. Shoot him too? Why not shoot everyone and invade Poland? In fifty years', thirty years', ten years' time the world will be very nearly back on its old course. History always has a great weight of inertia.
Almost always . . .
At circle time, when the walls between this and that are thinner, when there are all sorts of strange leakages
. . . Ah, then choices are made, then the universe can be sent careening down a different leg of the well-known Trousers of Time.
But there are also stagnant pools, universes cut off from past and future. They have to steal pasts and futures from other universes; their only hope is to batten on to the dynamic universes as they pass through the fragile period, as remora fish hang on to a passing shark. These are the parasite universes and, when the crop circles burst like raindrops, they have their chance . . .
* * *
Lancre castle was far bigger than it needed to be. It wasn't as if Lancre could have been bigger at one time; inhospitable mountains crowded it on three sides, and a more or less sheer drop occupied where the fourth side would have been if a sheer drop hadn't been there. As far as anyone knew, the mountains didn't belong to anyone. They were just mountains. The castle rambled everywhere. No one even knew how far the cellars went.