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.