The Science of Discworld Revised Edition

most evident rule seems to be ‘There are no rules’, apart perhaps from the one that could be expressed scientifically as ‘Excreta Occurs’. As the Harvard Law of Animal Behaviour puts it: ‘Experimental animals, under carefully controlled laboratory conditions, do what they damned well please.’ Not only animals: every golfer knows that something as simple as a hard, bouncy sphere with a pattern of tiny dots on it never does what it’s supposed to do. And as for the weather …
    Science has now divided into two big areas: the life sciences, which tell us about living creatures, and the physical sciences, which tell us about everything else. Historically, ‘divides’ is definitely the word – the scientific styles of these two big divisions have about as much in common as chalk and cheese. Indeed, chalk is a rock and so clearly belongs to the geological sciences, whereas cheese, formed by bacterial action on the bodily fluids of cows, belongs to the biological sciences. Both divisions are definitely science, with the same emphasis on the role of experiments in testing theories, but their habitual thought patterns run along different lines.
    At least, until now.
    As the third millennium approaches, more and more aspects of science are straddling the disciplines. Chalk, for instance, is more than just a rock: it is the remains of shells and skeletons of millions of tiny ocean-living creatures. And making cheese relies on chemistry and sensor technology as much as it does on the biology of grass and cows.
    The original reason for this major bifurcation in science was a strong perception that life and non-life are extremely different. Non-life is simple and follows mathematical rules; life is complex and follows no rules whatsoever. As we said, Down Here looks very different from Up There.
    However, the more we pursue the implications of mathematical rules, the more flexible a rule-based universe begins to seem. Conversely, the more we understand biology, the more important its physical aspects become – because life isn’t a special
kind
of matter, so it too must obey the rules of physics. What looked like a vast, unbridgeable gulf between the life sciences and the physical sciences is shrinking so fast that it’s turning out to be little more than a thin line scratched in the sand of the scientific desert.
    If we are to step across that line, though, we need to revise the way we think. It’s all too easy to fall back on old – and inappropriate – habits. To illustrate the point, and to set up a running theme for this book, let’s see what the engineering problems of getting to the Moon tell us about how living creatures work.
    The main obstacle to getting a human being on to the Moon is not distance, but gravity. You could
walk
to the Moon in about thirty years – given a path, air, and the usual appurtenances of the experienced traveller – were it not for the fact that it’s uphill most of the way. It takes energy to lift a person from the surface of the planet to the neutral point where the Moon’s pull cancels out the Earth’s. Physics provides a definite lower limit for the energy you must expend – it’s the difference between the ‘potential energy’ of a mass placed at the neutral point and the potential energy of the same mass placed on the ground. The Law of Conservation of Energy says that you can’t do the job with less energy, however clever you are.
    You can’t beat physics.
    This is what makes space exploration so expensive. It takes a lot of fuel to lift one person into space by rocket, and to make matters worse, you need more fuel to lift the
rocket
… and more fuel to lift the fuel … and … At any rate, it seems that we’re stuck at the bottom of the Earth’s gravity well, and the ticket out
has
to cost a fortune.
    Are we, though?
    At various times, similar calculations have been applied to living creatures, with bizarre results. It has been ‘proved’ that kangaroos can’t jump, bees can’t fly, and birds can’t get enough energy from their food to power their search for the food in the first place. It has even been ‘proved’ that life is impossible because living systems become more and more ordered, whereas physics implies that all systems become more and more disordered. The main message that biologists have derived from these exercises has been a deep scepticism about the relevance of physics to biology, and a comfortable feeling of superiority,