Science of Discworld

WAYS TO LEAVE OUR PLANET

RINCEWIND'S IMPASSIONED SPEECH HAS A POINT. If you think he's overstating his case, and that the Earth is really an idyllic place to live, bear in mind that he's been on our planet a lot longer than we have, and he's seen a lot that we've missed, because we experience the world on a much shorter timescale than the wizards have done. We think the planet's a great place. We grew up here. We were made for it, and it's just right for us ... at the moment. Tell that to the dinosaurs. You can't, can you. That's the point.

We're not suggesting that you sell up everything and start build­ing a lifeboat. But even the United States congress is beginning to wonder just how safe our planet really is, and politicians are not usually known for taking long-term views. The sight of Shoemaker-Levy 9 smashing into Jupiter raised a few political eyebrows. Tentative schemes are afoot to set up a defence system against incoming comets and asteroids. Spotting them early enough is the trick. Find them quickly, and a modest little rocket motor can save our planetary bacon.

It is in many ways amazing that life on Earth has survived every­thing that the universe has so far thrown at it. Evolution runs on Deep Time, less than a hundred million years hardly counts. Life is extremely resilient, but individual species are not. They last a few million years and then they become obsolete. Life persists by changing, by being a series of opening chapters. But, being human, we'd like to see our own story turn into at least a block­buster dekalogy.

We can take small comfort in one thing. Although right now we don't worry enough about incoming disaster from Up There, we do worry a lot about home-grown disaster Down Here: nuclear warfare, biological warfare, global warming, pollution, overpopulation, destruction of habitat, burning of the rainforests, and so on. However, there's no danger that human actions will wipe out the planet. Compared to what nature has already done, and will do again, our activities barely show up. One large meteorite packs more explosive power than all human wars put together, a hypothetical World War III included. One Ice Age changes the climate more than a civilization's worth of carbon dioxide from car exhausts. As for something like the Deccan Traps ... you wouldn't want to know how nasty the atmosphere could become.

No, we can't destroy the Earth. We can destroy ourselves.

No one would care. The cockroaches and the rats will come back, or if the worst comes to the worst the bacteria miles below ground will start to write a new opening chapter in the Book of Life. Someone else will read it.

If we really deserve the name Homo Sapiens, then we can do at least two things to improve our chances. First, we can learn to man­age our impact on the environment. The fact that nature deals the occasional death blow doesn't hand us an excuse to imitate it. We invented ethics. Our environment is sufficiently buffeted by various forces that the last thing it needs is humanity throwing extra span­ners in the works. At the most selfish level, we might be buying ourselves some time.

We could use that time to put some of our eggs in another bas­ket.

One of the great dreams of humanity has been to visit other worlds. It's starting to look as though this might be a very good idea, not just for fun and profit, but for survival.

We'd better say right now that none of this is science fiction. Or, rather, yes, it is science fiction, it's the very stuff of science fiction, because some of the best science-fiction writers (you don't see their stuff on TV) have been dealing with it for many decades. But that does not mean it's not real. Ices Ages happen. Big, big rocks come screaming out of the sky, and you need rather more than Bruce Willis flying the Space Shuttle as if it was the Millennium Falcon to stop them.

Our urge to explore the universe may be just another case of monkey curiosity, but there seems to be a deep impulse that urges us to find new lands to map and new worlds to conquer. Maybe there's an inbuilt urge to spread out, one leopard can't eat all of you if you spread out.

It is an urge that has driven us into every corner and crevice of our own planet, from the ice-floes of the Arctic to the deserts of Namibia, from the depths of the Mariana Trench to the peak of Everest. Most of us incline to Rincewind's view of a comfortable lifestyle and much prefer to stay at home, but a few are too restless to be happy anywhere for very long. The combination is a powerful one, and it has shaped our species into something very unusual, with collective capabilities beyond the understanding of any indi­vidual. We may not always use that combination wisely, but without it we would be greatly diminished. And it's offering a real opportu­nity.

Even a dream can work miracles. When Columbus (re-)discov-ered America, and Europe found out that it existed, he was looking for a new route to the Indies. He had convinced himself, on grounds that most scholars at the time found totally spurious, that the Earth was considerably smaller than was generally thought. He calculated that a relatively short voyage westward, from Africa, would lead to Japan and India. The scholars were right, Columbus was wrong, but it is Columbus that we remember, because he made the world smaller. He had the courage to set sail into an empty sea, sustained only by the belief that there was something important on the other side.

At least we can see where we ought to go. Columbus had to back a hunch.

Apollo-11 was the first practical method for getting out of the Earth's gravity well altogether. By this we don't mean that the Earth's gravitational pull becomes zero if you go far enough away, which is a common misconception: we mean that if you go fast enough, then the Earth's gravity can never pull you back down. Celestial mechanics operates in the phase space of distance and velocity, its 'landscape' involves speeds as well as lengths. Only when we understood enough about gravity and dynamics to appre­ciate this point did we stand any chance of making technology like Apollo work.

You can see this clearly from earlier suggestions, which were imaginative, in an earthbound sort of way, but fantastic and impractical, at least on Roundworld. In 1648 Bishop John Wilkins listed four possible ways to leave the ground: enlist the aid of spir­its or angels, get a lift from birds, fasten wings to your body, or build a flying chariot. If we wanted to be charitable, we could interpret the last two as aircraft and rockets, but Wilkins was clearly unaware that the Earth's atmosphere doesn't extend all the way to the Moon. A sixteenth-century engraving by Hans Schauffelein depicts Alexander the Great carried into space by two griffins, no notice­able improvement. Bernard Zamagna conceived of an aerial boat, and others suggested the use of balloons.

Every age fantasized about technology that already existed. In Jules Verne's From the Earth to the Moon of 1865 the journey was accomplished by firing a space capsule from a huge gun in Florida; its 1870 sequel Around the Moon involved a series of such capsules, forming a space train. Verne got Florida right, he knew that the Earth's spin produces centrifugal force, which helps the capsule to leave the planet more easily, and he knew that this force was great­est at the equator. Since the protagonists in his book were American, Florida was the best bet. When NASA started launching rockets, it came to the same conclusion, and the space facility at Cape Canaveral was born.

Big guns have deficiencies, such as a tendency to laminate pas­sengers to the floor because of rapid acceleration, but modern technology does make it possible to avoid this by applying the accel­eration gradually. Rockets are more practical from the engineering point of view. In 1926 Robert Goddard invented the liquid fuel rocket. The first one rose to the dizzy height of 40 feet (12.5 m). Rockets have come a long way since then, taking men to the Moon and instruments to the edge of the solar system. And they are much better rockets. Even so, there's something ... inelegant about heading off the planet on a giant disposable firework.

Until recently, there has been a general assumption that the energy to get into space has to be carried with the craft. However, we already have the beginnings of one way to get off the Earth that keeps the power source firmly on the ground. This is laser propul­sion, in which a powerful beam of coherent light is aimed at a solid object and literally pushes it along. It takes a lot of power, but pro­totypes invented by Leik Myrabo have already been tested at the High Energy Laser System Test Facility at White Sands. In November 1997 a small projectile reached a height of 50 feet (15m) in 5.5 seconds; by December this had been improved to 60 feet (20 m) in 4.9 seconds. This may not sound impressive, but compare with Goddard's first rocket. The method involves spinning the pro­jectile at 6000 revolutions per minute to achieve gyroscopic stability. Then 20 laser pulses per second are directed towards a specially shaped cavity, heating the air beneath the craft and creat­ing a pressure wave of thousands of atmospheres with temperatures up to 30,000° Kelvin, and that's what propels the projectile. At higher altitudes the air becomes very thin, and a similar craft would need an onboard fuel source. Fuel would be pumped into the cav­ity to be vapourized by the laser A megawatt laser could lift a 2-pound (1 kg) craft into orbit.

It is also a very powerful weapon…

Another possibility is power beaming. It is possible to 'beam' electromagnetic power from the ground in the form of microwaves. This isn't just fantasy: in 1975 Dick Dickinson and William Brown beamed 30 kilowatts of power, enough for thirty electric fires -over a distance of one mile. James Benford and Myrabo have sug­gested launching a spacecraft using millimetre range microwaves which are not attenuated by the atmosphere. This is a variation on the laser method and would use the same kind of projectile.

Both of these methods rely on a lot of raw power, betraying traces of the basic engineering assumption that getting into space needs a lot of energy to overcome the Earth's gravity. They do have the advantage that the raw power is just sitting on the planet; the 1,000 megawatt power station your laser launcher would require could generate for the National Grid when a launch wasn't going on.

A method of greater subtlety is the bolas, first proposed in the 1950s. Traditionally, a bolas is a hunting device made by tying three weights to strings and then tying the ends of the strings together. When thrown, it spins, pulling the weights apart, until the strings hit the target, at which point the weights spiral rapidly inwards and deal a killing blow. The same sort of device could be set up in a ver­tical plane above the equator, a bit like a giant ferris wheel with only three spokes. On the ends of the spokes would be pressurized cab­ins. The lowest part of the bolas's swing would be somewhere in the lower atmosphere, the top part way out in space. You would fly up in an aircraft, transfer to the first passing cabin, and be whisked skywards. The biggest obstacle to making such a machine is the cable, which has to be stronger than any known material, but car­bon fibre is well on the way to combining enough strength with enough lightness. Friction with the atmosphere would gradually slow the bolas's rotation down, but that could be compensated for using solar power arrays up in space.

The most celebrated device of this type, however, is the space elevator. We discussed this in the opening chapter, both as a serious technological idea and as a metaphor: here we give a few more details. In essence, the space elevator starts out as a satellite in geo­synchronous orbit. Then you drop a cable from it to the ground, and the rest is a matter of building a suitable cabin and, again, find­ing suitable material for the cable. You get the material up there using rockets or a whole cascade of bolases (and once you've got a small cable you can haul up the stuff for the bigger one). You only need to do all this once, so the cost is irrelevant over the longer term.

As we emphasized at the start of the book, once there is as much traffic is coming down as is going up, getting off the ground is essentially free and requires zero energy. At that point you build your interplanetary spacecraft up in space, using raw materials from the Moon or the asteroid belt. So the space elevator gives you a new place to start from, which is why we've used it as a metaphor for processes like life.

The idea of a space elevator was originated by the Leningrad engineer Y.N. Artsutanov in 1960, in an article in Pravda. He called it a 'heavenly funicular' and calculated that it could lift 12,000 tons per day into orbit. The idea came to the attention of Western scien­tists in 1966, thanks to John Isaacs, Hugh Bradner, and George Backus. These scientists weren't interested in getting into space: they were oceanographers, the only people seriously interested in hanging things on long cables. Except that they wanted to hang them down into the ocean bottoms, not up into space. The oceanog­raphers were unaware of the earlier Russian work, but Artsutanov's anticipation quickly became known to Western scientists too. The astronaut and artist Alexei Leonov published a painting of a space elevator in action in 1967.

Such a simple but mostly impractical idea is likely to occur to lots of people, but wouldn't become widely known because it's not practical with current or near-future technology, and that means that it will be re-invented independently by many people. In 1963 the science-fiction author Arthur C. Clarke considered suspending a lower satellite by cable from a geosynchronous one, as a way to increase the number of effectively geo- synchronous satellites for communication purposes. Later he realized that the same method would lead to the space elevator, an idea that he developed in his novel The Fountains of Paradise. In 1969 A.R. Collar and J.W. Flower also considered suspending a lower satellite by cable from a geosynchronous one And in 1975 Jerome Pearson suggested an 'orbital tower' that was essentially the same idea.

You can, of course, suspend more than one cable, once you've got one space elevator you can lift everything else that you need into space at low cost, so why not go the whole hog? Charles Sheffield's The Web Between the Worlds envisages a whole ring of space eleva­tors round the equator. This is what the wizards have found. Ironically, because human civilization has taken such a short time to develop, on evolutionary timescales, the wizards missed us ...

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 Kirn 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.