Science of Discworld

These discussions and experiments are lies-to-children: their aim is to convince the next generation of physicists that quantum-level systems do actually behave in the bizarre way that they do. Fine ... but it's got nothing to do with cats. The wizards of Unseen University, who know nothing about electrons but have an intimate familiarity with cats, wouldn't be fooled for an instant. Neither would the witch Gytha Ogg, whose cat Greebo is shut in a box in Lords and Ladies. Greebo is the sort of cat that would take on a ferocious wolf and eat it. In Witches Abroad he eats a vampire by accident, and the witches can't understand why the local villagers are so ecstatic.

Greebo has his own way of handling quantum paradoxes: 'Greebo had spent an irritating two minutes in that box. Technically, a cat locked in a box may be alive or it may be dead. You never know until you look. In fact, the mere act of opening the box will determine the state of the cat, although in this case there were three determinate states the cat could be in: these being Alive, Dead, and Bloody Furious.'

Schrodinger would have applauded. He wasn't talking about quantum states: he wanted to know how they led to ordinary, classical physics in the large, and he could see that the Copenhagen interpretation didn't have anything to say about that. So how do classical yes/no answers emerge from quantum Ant Country? The closest we have to an answer is something called 'decoherence', which has been studied by a number of physicists, among them Anthony Leggett, Roland Omnes, Serge Haroche and Luis Davidovich. If you have a big collection of quantum waves and you leave it to its own devices, then the component waves get out of step and fuzz out. This is what a classical object is 'really' like from the quantum standpoint, and it means that cats do, in fact, behave like cats. Experiments show that the same is true even when the role of the detector is played by a microscopic quantum object: a photon's wave function can collapse without any observers being aware, at the time, that it has done so. Even with a quantum cat, death occurs at the instant that the detector notices that the atom has decayed. It doesn't require a mind.

In short, Archchancellor, the universe always notices the cat. And a tree in a forest does make a sound when it falls, even if no one is around. The forest is always there.

NO, IT CAN'T DO THAT

ARCHCHANCELLOR RIDCULLY LOOKED AROUND at his colleagues. They'd chosen the long table in the Great Hall for the meeting, since the HEM was getting too crowded.

'All here? Good,' he said. 'Carry on, Mister Stibbons.'

Ponder sifted through his papers.

'I've, er, asked for this meeting,' he said, 'because I'm afraid we're doing things wrong.'

'How can that be?' said the Dean. 'It's our universe!'

'Yes, Dean. And, er, no. It's made up its own rules.'

'No, no, it can't do that,' said the Archchancellor. 'We're intelligent creatures. We make the rules. Lumps of rock don't make rules,'

'Not exactly', sir,' said Ponder, employing the phrase in its traditional sense of 'absolutely wrong'. 'There are some rules in the Project.'

'How? Is someone else meddling with it?' the Dean demanded. 'Has a Creator turned up?'

'An interesting thought, sir. I'm not qualified to answer that one. The point I'm trying to make is that if we want to do anything constructive, we've got to obey the rules.'

The Lecturer in Recent Runes looked down at the table in front of him. It had been laid for lunch.

'I don't see why,' he said. 'This knife and fork don't tell me how to eat.'

'Er ... in fact, sir, they do. In a roundabout way.'

'Are you trying to tell us that the rules are built in?' said Ridcully.

'Yes, sir. Like: big rocks are heavier than small rocks.'

'That's not a rule, man, that's just common sense!'

'Yes, sir It's just that the more I look into the Project, the more I'm not sure any more what common sense is. Sir, if we're going to build a world it has to be a ball. A big ball'

'That's a lot of outmoded religious nonsense, Mister Stibbons.'

'Yes, sir. But in the Project universe, it's real. Some of the ba ... the spheres the students have made are huge.'

'Yes, I've seen them. Showy, to my mind,'

'I was thinking of something smaller, sir. And ... and I'm pretty sure things will stay on it. I've been experimenting.'

'Experimenting?' said the Dean. 'What good does that do?'

The doors were flung open. Turnipseed, Ponder's assistant, hurried across to the table in a state of some agitation.

'Mister Stibbons! HEX has found something!'

The wizards turned to stare at him. He shrugged.

'It's gold,' he said.

'The Guild of Alchemists is not going to be happy about this,' said the Senior Wrangler, as the entire faculty clustered around the project. 'You know what they are for demarcation.'

'Fair enough,' said Ridcully, steering the omniscope. 'We'll just give them a few minutes to turn up, otherwise we'll go on as we are, all right?'

'How can we get it out?' said the Dean.

Ponder looked horrified. 'Sir! This is a universe! It is not a piggy-bank! You can't just turn it upside down, stick a knife in the slot and rattle it around!'

'I don't see why not,' said Ridcully, without looking up. 'It's what people do all the time.' He adjusted the focus. 'Personally I'm glad nothing can get out of the thing, though. Call me old fashioned, but I don't intend to occupy the same room as a million miles of exploding gas. What happened?'

'HEX says one of the new stars exploded.'

'They're too big to be stars, Ponder, We've been into this.'

'Yes, sir,' Ponder disagreed.

'They've only been around for five minutes.'

'A few days, sir. But millions of years in Project time. People have been dumping rubbish into it, and I think some just drifted in and ... I don't think it was a very well-made st, furnace in the first place.'

The exploding star was shrinking now, but flinging out a great halo of brilliant gases that even lit up one side of the rocky lumps the wizards had been making. Things want to come together and get big, Ponder thought. But when they're big enough, they want to explode. Another law.

'There's lead and copper here, too,' said Ridcully. 'We're in the money now, gentlemen. Except that in this universe there's nothing to spend it on. Even so, it seems we're making progress. You're looking peaky, Mister Stibbons. You ought to get some sleep.'

Progress, thought Ponder. Was that what they were making? But without narrativium, how did anything know?

It was day four. Ponder had been awake all night. He wasn't sure, but he thought he'd probably been awake the previous night, too. He may have nodded off for a while, pillowing his head on the growing pile of screwed-up pieces of paper, with the Project winking and twinkling in front of him. If so, he'd dreamed of nothing.

But he'd decided that Progress was what you made it.

After breakfast, the wizards looked at the ball which currently occupied the centre of the omniscope.