'Give the man a small cigar!' said Sweeper jubilantly. That's the big problem, Mister Vimes. And the answer, our Abbot tells us, is that it is in lots of places at once. Ah, here's the tea. And in order for it to be in lots of places at once, the multiverse is made up of a vast number of alternative universes. An oodleplex of oodleplexes. That's like the biggest number anyone can think of, ever. Just so's it can accommodate all the quantum. Am I going too fast for you?'
'Oh, that,' said Vimes. 'I know about that. Like, you make a decision in this universe and you made a different decision in another one. I heard the wizards talking about that at a posh reception once. They were . . . arguing about the Glorious Twenty-fifth of May.'
'And what were they saying?'
'Oh, all the old stuff. . . that it would have turned out different if the rebels had properly guarded the gates and the bridges, that you can't break a siege by a frontal attack. But they were saying that, in a way, everything happens somewhere 'And you believed them?'
'It sounds like complete thungas. But sometimes you can't help wondering: what would have happened if I'd done something different-'
'Like when you killed your wife?' Sweeper was impressed at Vimes's lack of reaction. 'This is a test, right?'
'You're a quick study, Mister Vimes.'
'But in some other universe, believe me, I hauled off and punched you one.' Again, Sweeper smiled the annoying little smile that suggested he didn't believe him. 'You haven't killed your wife,' he said. 'Anywhere. There is nowhere, however huge the multiverse is, where Sam Vimes as he is now has murdered Lady Sybil. But the theory is quite clear. It says that if anything could happen without breaking any physical laws, it must happen. But it hasn't. And yet the “many universes” theory works. Without it, no one would ever be able to make a decision at all.'
'So?'
'So what people do matters!' said Sweeper. 'People invent other laws. What they do is important. The Abbot's very excited about this. He nearly swallowed his rusk. It means the multiverse isn't infinite and people's choices are far more vital than they think. They can, by what they do, change the universe.' Sweeper gave Vimes a long look. 'Mister Vimes, you're thinking: I'm back in time, and damn me, I'm probably going to end up being the sergeant that teaches me all I know, right?'
'I've been wondering. The Watch would offer any gutter trash a job in those days, because of the curfew and all the spying. But look, I remember Keel and, yes, he did have a scar and an eye-patch but I'm sure as hell that he wasn't me.'
'Right. The universe doesn't work like that. You were indeed taken under the wing of one John Keel, a watchman from Pseudopolis who came to Ankh- Morpork because the pay was better. He was a real person. He was not you. But do you remember if he ever mentioned to you that he was attacked by two men not long after he got off the coach?'
'Hell, yes,' said Vimes. 'The muggers. He got this- he got his scar that way. A good old Ankh-Morpork welcome. But he was a tough man. Took 'em both down, no problem.'
'This time, there were three,' said Sweeper. 'Well, three's trickier, of course, but-'
'You're the policeman. You guess the name of the third man, Mister Vimes.' Vimes hardly had to think. The answer erupted from the depths of darkest suspicion. 'Carcer?'
'He soon settled in, yes.'
'The bastard was in the next cell! He even told me he'd grabbed some money.'
'And you're both stuck here, Mister Vimes. This isn't your past, any more. Not exactly. It's a past. And up there is a future. It might be your future. But it might not be. You want to go home now, leaving Carcer here and the real John Keel dead? But there'll be no home to go to, if you could do that. Because young Sam Vimes wouldn't get a swift course in basic policing from a decent man if you did. He'll learn it from people like Sergeant Knock and Corporal Quirke and Lance-Corporal Colon. And that might not be the worst of it, by a long way.' Vimes shut his eyes. He remembered how wet behind the ears he'd been. And Fred . . . well, Fred Colon hadn't been too bad, under the half-hearted timorousness and lack of imagination, but Quirke had been an evil little sod in his way and as for Knock, well. Knock had been Fred's teacher and the pupil wasn't a patch on the master. What had Sam Vimes learned from Keel? To stay alert, to think for himself, to keep a place in his head
free from the Quirkes and Knocks of the world, and not to hesitate about fighting dirty today if that was what it took to fight again tomorrow. He'd often thought he'd have been dead long ago if it wasn't for- He looked up sharply at the monk. 'Can't tell you that, Mister Vim.es,' said Lu-Tze. 'Nothing's certain, 'cos of quantum.'
'But, look, I know my future happened, because I was there!'
'No. What we've got here, friend, is quantum interference. Mean anything? No. Well... let me put it this way. There's one past, and one future. But there are two presents. One where you and your evil friend turned up, and one where you didn't. We can keep these two presents going side by side for a few days. It takes a lot of run time, but we can do it. And then they'll snap back together. The future that happens depends on you. We want the future where Vimes is a good copper. Not the other one.'
'But it must've happened!' snapped Vimes. 'I told you, I can remember it! I was there yesterday!'
'Nice try, but that doesn't mean anything any more,' said the monk. Trust me. Yes, it's happened to you, but even though it has, it might not, 'cos of quantum. Right now, there isn't a Commander Vimes-shaped hole in the future to drop you into. It's officially Uncertain. But might not be, if you do it right. You owe it to yourself, commander. Right now, out there, Sam Vimes is learning to be a very bad copper indeed. And he learns fast.' The little monk stood up. 'I'll let you think about that,' he said. Vimes nodded, staring at the gravel garden. Sweeper crept away quietly and went back into the temple. He walked to the other side of the office. He removed a strange-shaped key from around his neck and inserted it into a small door. The door opened. Brilliant sunlight burst ahead of him. He walked on, his sandals leaving the cold flagstones and walking on to well-trodden earth in broad, hot daylight. The river had a different course this far back in the past, and present- day residents of Ankh-Morpork would have been surprised at how pleasant it looked, seven hundred thousand years ago. Hippos sunbathed on a sandbank out in mid-stream and, according to Qu, were getting troublesome lately - he'd had to set up a little temporal fence around the camp at nights, so that any hippo trying to wander in among the tents found themselves back in the water with a headache. Qu himself, his straw hat protecting his head from the hot sun, was supervising his assistants in a vined-off area. Lu-Tze sighed as he walked towards it. There were going to be explosions, he knew it. It wasn't that he disliked Qu, the order's Master of Devices. The man was a sort of engineering equivalent of the Abbot. The Abbot had taken thousand-year-old ideas and put them through his mind in a new way, and
as a result the multiverse had opened for him like a flower. Qu, on the other hand, had taken the ancient technology of the Procrastinators, that could save and restore time, and had harnessed it to practical, everyday purposes, such as, yes, blowing people's heads off. It was something that Lu-Tze tried to avoid. There were better things to do with people's heads. As Lu-Tze approached, a line of joyful, dancing monks wove their way along a bamboo replica of a street, letting off firecrackers and banging gongs. As they reached a corner the last monk turned and lightly tossed a little drum into the outstretched arms of a straw dummy. The air shimmered, and the figure disappeared with a small thunderclap. 'Nice to see something not blowing anyone's head off,' said Lu-Tze, leaning on the vine rope. 'Oh, hello, Sweeper,' said Qu. 'Yes. I wonder what went wrong. You see, the body should have moved forward by a microsecond and left the head where it was.' He picked up a megaphone. Thank you, everyone! Places for another run! Soto, take over, please!' He turned to Lu-Tze. 'Well?'
'He's thinking about it,' said Sweeper. 'Oh, for heavens' sake, Lu-Tze! This is completely unauthorized, you know! We're supposed to prune out rogue history loops, not expend vast amounts of time keeping them going!'
'This one's important. We owe it to the man. It wasn't his fault we had the major temporal shattering just as he fell through the dome.'
'Two timelines running side by side,' moaned Qu. That's quite unacceptable, you know. I'm having to use techniques that are completely untried.'
'Yes, but it's only a few days.'
'What about Vimes? Is he strong enough? He's got no training for this!'
'He defaults to being a copper. A copper's a copper, wherever he is.'