The Science of Discworld Revised Edition

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
.
    Unfortunately, it does reduce the scope for asking interesting questions. Most of them have already been answered. Certainty rules. Mustrum Ridcully is not the kind of person who would tolerate an Uncertainty Principle, after all.
    Back in Roundworld, there is perhaps one point worth making.
    Just suppose there is
nothing else
. Arguments about intelligent life on other worlds have always been highly biased by the desires of those doing the arguing that there should
be
intelligent life on other worlds, and we three are among them. But the argument is a house of cards with no card on the bottom. We know of life on one world. Everything else is guesswork and naked statistics. Life may be so common through the universe that even the atmosphere of Jupiter is alive with Jovian gasbags and every cometary nucleus is home to colonies of microscopic blobules. Or there may be nothing alive at all, anywhere else but here.
    Perhaps intelligent life arose before humanity, and perhaps it will again when humanity’s span has become a rather complex layer in the strata. We can’t tell. Time does not simply, as the hymn says, bear all its sons away – it can easily see the disappearance of the entire continent on which they stood.
    In short, in a universe a billion Grandfathers long and a trillion Grandfathers wide, there may be just a few hundred thousand years on one planet where a species worried about something other than sex, survival, and the next meal.
    This is
our
Discworld. In its little cup of spacetime, humanity has invented gods, 3 philosophies, ethical systems, politics, an unfeasible number of ice-cream flavours and even more esoteric things like ‘natural justice’ and ‘boredom’. Should it matter to us if tigers are made extinct and the last orangutan dies in a zoo? After all, blind forces have