There are practical problems in making such a gadget, the main one(!) being that the wormhole will collapse too quickly for an object to pass through it, unless it is held open by threading ‘exotic matter’ with negative energy through it. Nonetheless, none of this is forbidden by the current laws of physics. So what of the paradoxes? It turns out that the laws of physics forbid genuine paradoxes, although they permit many apparent paradoxes. A useful technique for understanding the difference is known as a Feynman diagram, which is a picture of the motion of an object (usually a particle) in space and time.
For example, here is an apparent time travel paradox. A man is imprisoned in a concrete cell, locked from the outside, with no food, no water and no possibility of escape. As he sits in a corner in despair, waiting for death, the door opens. The person who has opened it is … himself. He has returned in a time machine from the future. But how (the paradox) did he get to the future in the first place? Well, a kind person opened the door and set him free …
There seems to be something very odd about the causality in this story, but the corresponding Feynman diagram shows that it violates none of the laws of physics. First, the man follows a space-time path that puts him inside the cell and then removes him from it through an opened door. This time-line continues into his future until he encounters a time machine. Then the time-line reverses direction, heading into the past, until he encounters a locked cell. He opens it, and his time-line reverses again, propelling him into his own future. So the man follows a single zig-zag path through time, and at every step the laws of physics hold good. Provided his time machine violates no physical law, of course.
If you try to ‘explain’ the grandfather paradox by this method, it doesn’t work. The time-line leading from grandfather to killer is severed when the killer returns; there is no consistent scenario, even in a Feynman diagram. So some stories of time travel are consistent with the laws of physics, and have their own kind of causal logic, albeit twisted; but other equally plausible stories are inconsistent with the laws of physics. You can rescue the Grandfather Paradox by assuming that changing the past in a logically inconsistent way switches you into a different alternate universe – say a quantum-mechanical parallel world. But then it wasn’t your grandfather that you killed, but the grandfather of an alternate you. So this ‘resolution’ of the Grandfather Paradox is a cheat.
Faced with all this, the way that the wizards handle the complications of time travel seems quite reasonable!
1 The superstition is common in the Black Country, in places like Wombourne and Wednesbury. Though that’s not why it’s called the Black Country. The thing about your Black Country is, it’s black. At least, it was black, with industrial grime and pollution, when it got its name. Some bits no doubt still are.
2 Schrödinger pointed out that quantum mechanics often gives silly answers like ‘the cat is half alive and half dead’. His intention was to dramatise the gap between a quantum-level description of reality and the world we actually live in, but most physicists missed the point and derived complicated explanations of why cats really are like that. And why the universe needs conscious observers to ensure that it continues to exist. Only recently did they twig what Schrödinger was on about, and come up with the concept of ‘decoherence’, which shows that superpositions of quantum states rapidly change into single states unless they are protected from interaction with the surrounding environment. And the universe doesn’t need us to make it hold together, sorry. See The Science of Discworld, with a cameo appearance of Nanny Ogg’s cat Greebo.
3 Discworld runs this far more sensibly. Heroes will have adventures.
4 Recall that Yossarian is a pilot in Joseph Heller’s Catch-22.
5 We use this word because it’s standard in science fiction, but UK English would require ‘alternative’.
6 Named after the physicist Enrico Fermi. See Evolving the Alien by Jack Cohen and Ian Stewart.
TWENTY-NINE
ALL THE GLOBE’S A THEATRE
THE ELVES DID NOT SPEND A LOT OF TIME in serious thought. They could control people who could do the thinking for them. They didn’t play music, they did not paint, they never carved stone or wood. Control was the talent, and it was the only one they had ever needed.
Nevertheless, there were ones who had survived for many thousands of years, and while they had no great intelligence they had accumulated that mass of observations, experience, cynicism and memory that can pass for wisdom among people who don’t know any better. One of the wisest things they did was not read.
They had found some clerks to read the play.
They listened.
Then, when it was over, the Queen said: ‘And the wizards have been showing great interest in this man?’
‘Yes, your majesty,’ said one of the old ones.
The Queen frowned. ‘This … play is … good. It treats us … kindly. We are firm but fair with mortals. We offer rewards to those who deal well with us. Our beauty is satisfactorily referred to. Our … issues with our husband are treated more romantically than I would like, but, nevertheless … it is positive, it enhances us, it places us yet more firmly in the human world. One of the wizards was actually carrying this.’
One of the senior elves cleared its throat. ‘Our grip is loosening, your majesty. Humanity is becoming more, shall we say, questioning?’
The Queen shot it a glance. But it was older than many Queens, and did not step back.
‘You think it will do us harm? Is it a plot against us?’
The senior elves looked at one another. The main reason that they thought it was a plot was that they were predisposed to see plots. In the court of Faerie, an inability to see it coming meant that it took you by the throat.
‘We think it may be,’ one said at last.
‘How? In what way?’
‘We know the wizards have been seen in the company of the author,’ said the elf.
‘Then perhaps they are endeavouring to stop him writing the play, have you thought of that?’ snapped the Queen. ‘Can you see any way in which those words harm us?’
‘We are agreed that we cannot … nevertheless, we have a sense that in some way—’
‘It is so simple! At last we are done some real honour and the wizards will try to stop it! Are you so stupid that you cannot see that?’
Her long dress swirled as she turned on her heel. ‘It will happen,’ she said. ‘I will see to it!’
The senior elves filed out, not looking at her face. They knew those moods.
On the stairs one said to the others: ‘Purely out of interest … can any of us put a girdle around the Earth in three minutes?’
‘That would be a very big girdle,’ said an elf.
‘And would you wish to be called Peaseblossom?’
The eyes of the old elf were grey, flecked with silver. They had seen horrible things under many suns, and in most cases had enjoyed them. Humans were a valuable crop, the elf conceded. There had never been a species like it for depth of awe, terror and superstition. No other species could create such monsters in its heads. But sometimes, it considered, they were not worth the effort.
‘I think not,’ it said.
‘Well, now, Will – do you mind if I call you Will? Oh, Dean, fetch Will another pint of this really unpleasant ale, will you? Now … where was I … oh yes, I really enjoyed that play of yours. Magnificent, I thought!’ Ridcully beamed. Around him, the inn hummed with life.
Will tried to focus. ‘Which one was that, good sir?’ he said.
Ridcully’s smile remained fixed, but began to unravel around the edges. He was never one for unnecessary reading.
‘The one with the king in it,’ he said, aiming for safety.
On the other side of the table Rincewind did some desperate pantomime.
‘The rabbit,’ said Ridcully. ‘The rat. The ferret. Sounds like … hat. Rat. Rodent. Thing with teeth.’
Rincewind gave up, leaned across and whispered.
/> ‘Something about the shrew,’ said Ridcully. Rincewind whispered a little harder.
‘The one about the tame shrew. The man married a shrew. A shrewish woman. Not a real shrew, obviously, haha. No one would marry a real shrew. It would be a completely foolish idea.’
Will blinked. He was not, as an actor and a writer, averse to alcohol bought by other people, and these people were being very good hosts. It was just that they seemed to be completely deranged.
‘Er … I thank you,’ he said. He was aware of being stared at, and also of a strange but not unpleasant animal smell. He turned on the bench and was rewarded with a grin. It occupied all the space between a deep hood and a jerkin. There were a couple of brown eyes, too, but it was the grin his gaze kept coming back to.
The Librarian raised his tankard and gave Will a friendly nod. This caused the grin to get bigger.
‘Now I’m sure you hear this all the time,’ said Ridcully, slapping Will so hard on the back that his drink slopped, ‘but we’ve got an idea for you. Dean, more ale all round, eh? It really is very weak stuff. Yes, an idea.’ He poked Will in the chest. ‘Too many kings, that’s the trouble. What the public wants now, what puts bums on seats—’
‘Feet,’ said Rincewind.
‘What?’
‘Bums on feet, Archchancellor. It’s mostly standing room in the theatre.’
‘Feet, then. Bums, anyway. Thank you, Dean. Cheers.’ Ridcully wiped his mouth delicately and turned his attention again to Will, who tried to avoid the prodding finger.
‘Bums on, haha, feets,’ he said, and blinked. ‘Funny thing, funny thing, something similar happened to us, ’smatterofact, few years ago, Midsummer’s Eve, these chaps were going to put on a play thingy for the king, next thing, elves all over the place, haha. Why, yes, Runes, I’ll have another if you’re paying, it’s far too sweet to be a serious drink. Where was I? Ah. Elves. What you’ve got to do, what you’ve gotta do … is … why aren’t you writing this down?’
In the morning Rincewind opened his eyes at the fourth attempt and with the assistance of both hands. There was a moment of brain lag, where the little wheels spun happily with no work to do, and then big horrible machinery cut in.
‘Whg d’hl der …’ he said, and then got control of his mouth as well.
Bits of last night crept out of hiding to do their treacherous dance before his eyes. He groaned.
‘We couldn’t have done that, could we?’ he muttered.
And memory said: that was only the start …
Rincewind sat up and waited until the world stopped moving.
He’d been on the floor in the library. The other wizards lay scattered around the room or sprawled across piles of books. The air smelled of beer.
A veil will be drawn over the following half an hour, and lifted to find the wizards sitting around the table.
‘It must’ve been the pork scratchings,’ said the Dean.
‘I don’t remember any pork scratchings,’ muttered Ponder.
‘Something crunchy, anyway. They may have been moving about.’
‘There’s no doubt in my mind that it was caused by all this travelling we’ve been doing,’ said Ridcully. ‘That sort of thing must take a terrible toll on the system. We’ve been concentrating so hard, d’yer see, that the moment we relaxed the strain we just unwound, like a big spring.’
The wizards brightened up. Rascally drunkenness was too much of an embarrassment to men who could sit through an entire meal at the UU high table, but time sickness … yes, that had a certain cachet. They could live with time sickness although, at the moment, they were wishing they didn’t have to.
‘That’s right!’ said the Lecturer in Recent Runes. ‘It wasn’t the fight!’
‘And it couldn’t possibly have been the carousing, which was really quite moderate by our standards,’ said the Dean.
‘In fact we didn’t get drunk at all!’ said the Chair of Indefinite Studies, brightly.
Unfortunately, Rincewind’s memory was literally treacherous. It worked perfectly.
‘So, then,’ he said, wishing that he didn’t have to, ‘we didn’t tell Will all that stuff?’
‘What stuff?’ said Ridcully.
‘All about our magical library, for one thing. And you kept saying “Here’s a good one, I bet you can use this” and you told him about those witches up in Lancre and how they got the new king on the throne, and that time the elves broke through, and how the Selachii and the Venturi families are always fighting—’
‘We did?’ said Ridcully.
‘Yes. And about the countries we’ve visited. Lots of things.’
‘Why didn’t someone stop me?’
‘The Dean did try. That’s when you hit him with the Chair of Indefinite Studies, I think.’
The wizards sat in ale-smelling gloom.
‘Should we have another try?’ said the Lecturer in Recent Runes.
‘What, and tell him to forget it all?’ said Ridcully. ‘Talk sense, man.’
‘Perhaps we could go back in time and stop ourselves telling—’
‘Don’t say that! No more of that!’ snapped the Archchancellor.
Rincewind pulled a copy of the play towards him. The wizards froze.
‘Go on,’ said Ridcully. ‘Tell us the worst. What did he write?’
Rincewind opened the book and read a couple of lines at random:
‘You spotted snakes, with double tongue;
Thorny hedgehogs, be not—’
‘No, no, no,’ muttered the Dean, his head in his hands. ‘Please tell me no one sang him the Hedgehog Song …’
Rincewind’s lips moved as he read on. He turned over a few pages. He flicked back to the beginning.
‘It’s all here,’ he said. ‘Same rather bad jokes, same unbelievable confusions, everything! Just as it was before! But it’s going to happen here!’
The wizards looked at one another and dared to share a smug expression.
‘Ah well, there we are then,’ said Ridcully, sitting back. ‘Job done.’
Rincewind turned some more pages. His recollections of the night were not coherent, but even a genius couldn’t have made sense out of a bunch of drunken wizards all talking at once.
‘Hex?’ he said.
The crystal ball said: ‘Yes?’
‘Will this play be performed in this world?’
‘That is the intention,’ said the voice of Hex.
‘And then what will happen?’
Hex told them, and added: ‘That is one outcome.’
‘Just a moment,’ said Ponder Stibbons. ‘There’s more than one outcome?’
‘Certainly. The play may not take place. Phase space contains a broadsheet account of a disruption of the first performance, followed by a fire in which a number of people died. Subsequently the theatres were closed and the playwright died during a riot. He was struck by a pike.’
‘You mean a halberd, of course,’ said Ridcully.
‘A pike,’ Hex repeated. ‘A fishmonger was involved.’
‘What happened to civilisation?’
Hex was silent for a moment, and then said: ‘Humanity failed by three years to leave the planet.’
THIRTY
LIES TO HUMANS
PLEASE TELL ME NO ONE SANG him the Hedgehog Song …
The Hedgehog Song, a Discworld ditty in the general tradition of Eskimo Nell, first made its appearance in Wyrd Sisters with its haunting refrain ‘The hedgehog can never be buggered at all’. The wizards have wielded the power of story with a vengeance. They have used it to prime their secret weapon, Shakespeare, and are convinced that he will prove more effective than a MIRVed ICBM. But before he’s launched, they’ve very properly started to worry about collateral damage: possible cultural contamination by the Hedgehog Song.
It is a consequence only marginally less dire than eternal elf-infestation, but on the whole, preferable.
In the real Roundworld, the power of story is just as great
as it is in the fictional counterpart. Stories have power because we have minds, and we have minds because stories have power. It’s a complicity, and all that remains is to unwrap it.
As we do so, bear in mind that Discworld and Roundworld are not so much different as complementary. Each, in its own estimation at least, gave birth to the other. On Roundworld, the Disc is seen as fantasy, the invention of an agile mind; Discworld is a series of stories (amazingly successful) along with ceramic models, computer games and cassette tapes. Discworld runs on magic, and on narrative imperative. Things happen on Discworld because people assume they will, and because some things have to happen to complete the story. From the standpoint of Roundworld, Discworld is a Roundworld invention.
The Discworld view is similar, but inverted. The wizards of Unseen University know that Roundworld is merely a Discworld creation, an unanticipated spin-off from an all-too-successful attempt to split the thaum and create the first self-sustaining magical chain reaction. They know this because they were there when it happened. Roundworld was deliberately created to keep magic out. Surprisingly, the magic-free vacuum acquired its own regulatory principle. Rules. Things happen on Roundworld because they are consequences of the rules. However, it is astonishingly difficult to look at the rules and understand what their consequences will be. Those consequences are emergent. The wizards discovered this to their cost, as every attempt to do something straightforward in Roundworld – like creating life or jump-starting extelligence – went seriously awry.
The Science of Discworld II Page 35