Is the space elevator anything other than a wild fantasy? Could one really be built in the near future? In 2001 two NASA teams carried out feasibility studies, and both concluded that the space elevator is technologically possible. Just. David Smitherman, who led one team, reckons it could be in place by 2100.
The main problem is the cable. The tension in the cable is lowest near the ground, and highest at the top, because each section of cable has to support only the weight of cable below it. So the cable should be made thin at the bottom, and thicker towards the top. The big question is: which material has enough tensile strength? Steel won’t do: a steel cable 4 inches (10 cm) wide at the bottom would have to be 2.5 trillion miles (4 trillion km) across at the top. (This is an engineer’s way of saying ‘don’t use steel’: it’s too heavy and the stress goes up extremely fast as the cable gets longer.) Kevlar would be more practical: the top would then need to be only 1600 metres across – just over a mile wide. But even this is not practical enough.
For the size to be acceptable, the cables tensile strength needs to be at least 62.5 gigapascals – 30 times stronger than steel and 17 times stronger than Kevlar. Such materials do exist: the best known is the carbon nanotube, a molecule of carbon shaped like a hollow cylinder and related to the famous molecule buckminsterfullerene, which is made from 60 atoms of carbon and is shaped like a soccer ball. The tensile strength of a carbon nanotube is at least 130 gigapascals, more than twice as strong as necessary. The only snag is, that right now the longest carbon nanotubes we can make extend for only a few millionths of a metre. But if that could be increased to 4 millimetres, then the nanotubes could be embedded in a composite material with the necessary strength.
A second problem is the base. The higher the bottom of the cable is off the ground, the more material is saved at the top, where most of the mass is. This is why the cable in our story has a huge ‘etiolated whelk’ at its base. The NASA study concluded that a tower at least 6 miles (10 km) high would be best. It could be built on a mountaintop, to reduce the height needed, but if the cable were to snap, the main debris would then fall on land. So a tower in the ocean at the equator would make more sense. Current construction methods could, in principle, build a 12-mile (20-km) tower.
The final design problem is how to transport capsules up and down the cable. Whatever method is used, it has to be low on maintenance and high on speed. Magnetic levitation looks good.
After that, it’s mostly a question of protecting the cable against meteor-strikes and incoming high-energy particles. A piece of cake.
Having built your space elevator, you’re now in a position to colonize other worlds. The obvious first destination is Mars. You get there in a cloud of small, mass-produced ships, and once you’ve got there one of the first things you do is drop down a cable and build a Martian space elevator. You’re up in orbit anyway, so why not take advantage of the fact? Again, this is the metaphorical aspect of the space elevator: as soon as just one exists, it opens up a vast range of new possibilities. However, you’ll probably need to land a team by some other method in order to construct the complex at the bottom to which the cable will be tethered.
Mars isn’t a great place to live, so the next step is to terraform it – to make it more earthlike. There are reasonably plausible methods for doing that, detailed at length in Kim Stanley Robinson’s series Red Mars, Green Mars, Blue Mars. Mars is no improvement when it comes to meteor-strikes, but at least the colony on Mars is unlikely to get wiped out at the same time as the main population on Earth. Because life is reproductive, if one of them does get wiped out, it can quickly be re-colonized from the other. After a few centuries, you’d hardly notice any difference. Still, it may be better to be more ambitious and go to the stars. By the time we’re ready for that, we’ll have interferometer telescopes good enough to spot which stars have suitable planets. The only problem, then, will be to get there.
There are plenty of suggestions, and we won’t add to them. Think of mid-Victorians predicting life in the 1990s. The dynamic of extelligence is emergent or, to put it another way, we haven’t the faintest idea what we’ll think of next but it’ll probably surprise us.
One way, if all else fails, is the Generation Ship – a huge vessel that can hold an entire city of people, who live, breed, educate, and die throughout the centuries-long journey. Make it big and interesting enough, and they may even lose interest in the destination. The Discworld almost counts as one of these; it’s on a journey, the inhabitants don’t know where they’re going, the designers have given it a small controllable sun (thus doing away with all those nasty fluctuations) and no less than five bio-engineered creatures positively delight in clearing local space of intrusive debris …
Back on our world, you could take a really long-term view and seed the galaxy with genetically engineered bacteria, carefully tailored so that whenever they find a suitable planet they eventually evolve into humanoid life (or life, at least). We would die out, but maybe our fleet of cheap, slow ships might seed a few new Earths somewhere.
There’s no shortage of ideas. Some might even be practical. The galaxy beckons. We might die trying – but since we’re going to die anyway, why not try?
And what will we find out there? Will we find a radically different kind of ‘space elevator’, for instance? Well, if there are aliens that live on neutron stars, as Robert L. Forward describes in Dragon’s Egg, then they might escape by tilting their world’s magnetic axis, turning it into a pulsar, and surfing its plasma jet. Perhaps all those pulsars were formed in this way. Like any ‘space elevator’, if you can manage the trick once, the rest is easy. The inhabitants of one neutron star managed it, and colonized all the others, founding the Pulsar Empire …
And since we can envisage new kinds of physical space elevator, there must surely also be new kinds of metaphorical space elevator. Not just aliens a bit like us, but radically different new kinds of life.
What else could live on a neutron star?
They’re waiting.
FORTY-SEVEN
YOU NEED CHELONIUM
‘THAT,’ SAID THE Dean, ‘was a very unpleasant business. Good thing we weren’t really there.’
Rincewind was sitting at the end of the long table, his chin on his hand.
‘Really?’ he said. ‘You thought that was bad? Try having a comet land on you. That really makes your day.’
‘It was the music that really got on my nerves,’ said the Senior Wrangler.
‘Oh, well, good job the planet’s a snowball, then,’ said Rincewind.
‘I call this meeting to order,’ said Ridcully, thumping the table. ‘Where’s the Bursar?’
The wizards looked around the main hall of the High Energy Magic building.
‘I saw him half an hour ago,’ the Dean volunteered.
‘We are quorate, nevertheless,’ said Ridcully. ‘Now … the magic flux is almost run down, although HEX reports that the model universe appears to be continuing on internal power. Amazing the way the whole place seems to strive to keep existing. However … gentlemen, the project is at an end. All it is has taught us is that you can’t make a world out of bits and pieces. You need chelonium for a proper world. And you certainly need narrativium, otherwise the life you get is a lot of opening chapters. A comet is no way to end a story. Ice and fire … that’s very primitive.’
‘Poor old crabs,’ said the Senior Wrangler.
‘Goodbye, lizards,’ said the Dean.
‘Farewell, my limpet,’ said the Lecturer in Recent Runes.
‘What were the ones that left?’ said Ponder.
‘Er …’ said Rincewind.
‘Yes?’ said the Archchancellor.
‘Oh, nothing. I had a thought … but it couldn’t possibly work.’
‘Some of the bears seemed quite bright,’ said Ridcully, who had naturally sided with a lifeform that resembled him in several particulars.
‘Yes, yes, it was probably the bears,’ said Rincewind quickly.
&
nbsp; ‘We couldn’t watch the whole world all the time,’ said Ponder. ‘Something could have evolved quickly, I suppose.’
‘Yes, that’s right, something probably evolved quickly,’ said Rincewind. ‘I shouldn’t think there was any unauthorized interference in any way.’
‘Good luck to them, whatever shape they’re in,’ said Ridcully. He assembled his papers. ‘That’s it, then. I won’t say it hasn’t been an interesting few days, but reality calls. Yes, Rincewind?’
‘What are we going to do with the snow globe – I mean, the world?’ said Rincewind.
As one wizard, they looked across at the world spinning gently in its dome.
‘Is it any use to us, Mister Stibbons?’ said Ridcully.
‘As a curiosity, sir.’
‘This university is stuffed with curiosities, young man.’
‘Well, then … only as very large paperweight.’
‘Ah. Rincewind … you are the Professor of Cruel and Usual Geography, so I suppose this is right up your street –’
There was a rattle from HEX’s tray. Ponder pulled out the paper.
It said: +++ The Project Must Be Kept Safe +++
‘Fine. Rincewind can put it on a high shelf so that it doesn’t get knocked,’ said Ridcully, rubbing his hands together.
+++ Recursion Is Occurring +++
Ridcully blinked at the writing.
‘Is that a problem?’
HEX creaked. There was a flurry of activity in the ant tubes. Eventually the write-out clattered for some time.
Ponder picked up the message.
‘Er … it’s addressed to Mrs Whitlow,’ he said. Er … it’s rather odd …’
Ridcully looked over his shoulder.
‘“Don’t Dust It”,’ he read.
‘She’s a devil with a duster,’ said the Senior Wrangler. ‘The Dean nails his door shut when he leaves his study.’
The write-out clattered again.
‘“This Is Important”,’ Ponder read.
‘Not a problem, not a problem,’ said Ridcully. ‘So on to the next item. Ah, yes. We have to shut down the reacting engine. No, don’t get up, Rincewind, I’ve had the door locked. The interior of the squash court is still just a tiny bit not entirely completely safe, is that right, Mr Stibbons?’
‘Very definitely!’
‘And therefore the area within it quite clearly counts as –’
‘Let me guess,’ said Rincewind. ‘It’s cruel and unusual geography, yes?’
‘Well, done, that man! And all you have to do –’
A sound that had been on the limit of hearing suddenly descended through the scales. And there was silence.
‘What’s that?’ said Ridcully.
‘Nothing,’ said Rincewind, with unusual accuracy.
‘The reacting engine has shut down,’ said Ponder.
‘By itself?’
‘Not unless it can pull its own levers, no …’
The wizards clustered around the door to the old squash court. Ponder held up his thaumometer.
‘There’s hardly any flux now,’ he said. ‘It’s practically background … Stand back …’
He opened the door.
A couple of white pigeons flew out, followed by a billiard ball. Ponder pulled aside a cluster of flags of all nations.
‘Just natural fallout,’ he called out. ‘Oh …’
The Bursar ambled around the side of the reacting engine, waving a squash racket.
‘Ah, Ponder,’ he said. ‘Have you wondered if Time isn’t simply Space rotated through a right angle?’
‘Er … no …’ said Ponder, watching the man carefully for signs of thaumic breakdown.
‘It would certainly make pretzels very interesting, don’t you think?’
‘Er … have you been playing squash, sir?’ said Ponder.
‘You know, I’m really coming to believe that a closed contour is a boundary, up to parametrization, if and only if it is homotopic to zero,’ said the Bursar. ‘And, for preference, coloured green.’
‘Did you touch any switches, sir?’ said Ponder, maintaining a careful distance.
‘This thingy here does make some shots very difficult,’ said the Bursar, hitting the reacting engine. ‘I was trying to hit the rear wall around last Wednesday.’
‘I think perhaps we should leave,’ said Ponder in a clear, firm tone. ‘It will soon be teatime. There will be jelly,’ he added.
‘Ah, the fifth form of matter,’ said the Bursar brightly, following Ponder.
The other wizards were waiting just outside the door.
‘Is he all right?’ said Ridcully. ‘I mean by general bursarial standards, of course.’
‘It’s hard to tell,’ said Ponder, as the Bursar beamed at them. ‘I think so. But the reacting engine must had been putting out quite a high flux when he went in.’
‘Perhaps none of the thaumic particles hit him?’ said the Senior Wrangler.
‘But there’s millions of them, sir, and they can pass through anything!’
Ridcully slapped the Bursar on the back.
‘Bit of luck for you, eh, Bursar?’
The Bursar looked puzzled for a moment, and then vanished.
FORTY-EIGHT
EDEN AND CAMELOT
THIS BOOK WASN’T called The Religion of Discworld for a reason, although – Heaven knows – there is plenty of raw material.1 All religions are true, for a given value of ‘truth’.
The disciplines of science, however, tell us that we live on a world formed from interstellar debris some four billion years ago in a universe which itself is about 15 billion years old (which is science-speak for ‘a very long time’); that in the ensuing years it has been pummelled and frozen and re-arranged on a regular basis; that despite or rather because of this, life turned up very quickly and seems to spring back renewed and re-formed from every blow; and that we ourselves evolved on this planet and, with the suddenness of a bursting dam, became Top Species in a very short period of time.
Actually, science tells us that many cockroaches, bacteria, beetles, and even small mammals might argue that last statement, but since they are not good at debate and can’t speak, who cares what they think? Especially since they can’t, eh? A key thing about big brains is this: they know big brains are good.
Most of us don’t think like scientists. We think like the wizards of Discworld. Everything in the past was leading inevitably to Now, which is the important time.
While the news that the Earth is a small planet in a dull part of the universe has caught on in recent centuries, it’s only in the last few decades that the words ‘the Earth’ have come to mean, for a significant proportion of any society, ‘the planet’ rather than ‘the soil’.
It was probably those photographs of the Earth seen from the Moon that did it. We saw the whole planet as a single thing, rather than just the bit of it that we were standing on. And it looked fragile, and kind of lonely …
We watch the fireworks as great balls of ice plummet into the atmosphere of a nearby planet and, although any one of them would have seriously troubled the Earth, the event was just that: a firework display. As one old lady told a news reporter, ‘that sort of thing happens in Outer Space’. But we’re in Outer Space, too, and it might pay us to get good at it.
The dinosaurs were not, as suggested in Jurassic Park, ‘selected for extinction’ – they were clobbered by a very large rock, and/or its after-effects. Rocks don’t think.
The dinosaurs were in fact doing very well, and had merely neglected to develop three-mile thick armour plating. They may even have evolved something that we’d recognize as ‘early civilization’; we shouldn’t underestimate how much the surface of the planet can change in 65 million years. But rocks don’t care, either.
But even if the rock had missed, there were other rocks. And if they had missed too, then we should be aware that the planet has other, home-grown means of disposal.
Evidence is emerging that suggests
that other extinctions were caused by ‘natural’ but catastrophic changes in the planet’s atmosphere. A case is being made that indicates that the very existence of life on Earth will, periodically, trip a catastrophe.
Rocks don’t mind.
This will probably not happen tomorrow. But, one day, it will. And then Rincewind’s kaleidoscope is shaken up for a new pretty pattern.
Eden and Camelot, the wondrous garden-worlds of myth and legend, are here now. This is about as good as it ever gets. Mostly, it’s a lot worse. And it won’t stay like this for very long.
There are, perhaps, choices. We could leave. We’ve dealt with that. Considerable optimism is required. But there might be other small blue planets out there … By definition, though, Earthlike worlds will have life on them. That’s why they’ll be Earthlike. And the trouble is that the more Earthlike it is, the more troublesome it would be. Don’t worry about the laser-wielding monsters – you can talk to them, if only about lasers. The real problem is more likely to be something very, very small. In the morning you get a rash. In the afternoon, your legs explode.2
The other ‘choice’ is to stay. We may be lucky – we tend to be. But we won’t be lucky forever. The average life of a species is about five million years. Depending on how you define humanity, we may already be close to the average.
A useful project, and one that’s much cheaper to achieve, is to leave a note to the next occupiers, even if it is only to say ‘We Were Here’. It may be of interest to a future species that even if they are alone in space, they’re not alone in Time.
We may already have left our marker. It depends on how long things will really last on the Moon, and if, in a hundred million years, anyone else feels it necessary to go there. If they do, they may find the abandoned descent stages of the Apollo Moon landers. And they’ll wonder what a ‘Richard M. Nixon’ was.
How much luckier are the inhabitants of Discworld. They know they live on a world made for people. With a large hungry turtle, not to mention the four elephants, interstellar debris becomes lunch rather than catastrophe. Large-scale extinction has more to do with magical interference than random rocks or built-in fluctuations; it may have the same effect, but at least there is someone to blame.
The Science of Discworld Revised Edition Page 40