The Science of Discworld Revised Edition

be the same in a hundred million years ’ time. But it would be different tomorrow.
    In the deserted High Energy Building, H EX turned the omniscope outwards, homing in on signs of the strange new life.
    It found comet cores, strung on cables thousands of miles long. There were dozens of these trains, many millions of miles from the frozen world, accelerating into the abyss between the stars.
    Lights twinkled on their surfaces. The extelligence inside appeared to be travelling hopefully.
    A yellow cylinder tumbled gently across the darkness.
    It was empty.

FORTY-SIX
WAYS TO LEAVE YOUR 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