The Science of Discworld IV

tidily distinguished stages.
    So let’s not start with complex development, like acorns and eggs, when thinking about origins. Let’s start with something genuinely simpler: a thunderstorm. Before the storm, there is a time of cool, clear skies, clouds moving with the wind, probably a weather front. What we don’t see, because it’s invisible, is the static electricity building up in the clouds. Clouds are masses of water droplets, billions of tiny spheres of liquid water in a mass of water vapour: a saturated solution of water in air. The droplets and vapour rise to the top of the cloud; then they fall back through the cloud, not quite dropping out as rain, and the cycle repeats. Many do drop out as rain when the storm starts, of course.
    Clouds are very active structures, with massive circulations. They look gauzy and simple, but internally they are a mass of water-droplet and ice-particle currents. Each droplet and particle carries a tiny electric charge, and the cloud as a whole also acquires an electric charge, for much the same reason that your nylon underwear acquires an electrical charge opposite to that of your body. So the cloud has the opposite charge to that of the hills it passes over, a clear recipe for trouble. As the charge builds, the electric potential between the cloud and the ground gets bigger. Eventually it becomes big enough for lightning to make its own path between cloud and ground, following a trail of lower-resistance ionised air. Metal spikes sticking up from the ground, or on the top of tall buildings like churches, provide particularly good targets. In the absence of those, a person walking on a hill might be the unlucky Earth-end of a strike.
    A thunderstorm seems simpler than an acorn becoming an oak, because it doesn’t need lots of intricate organisation. But even a thunderstorm is not as simple as we tend to imagine: we don’t know how the electric potential builds. There are 16 million thunderstorms each year on Roundworld, but we’re still not really sure how they happen. No wonder we have trouble understanding how an acorn becomes an oak.
    As for the
origin
, the beginnings of a storm, the beginnings of anything … To explain thunderstorms, do we have to explain clouds? The constituents of the atmosphere? Static electricity? The elements of physics and physical chemistry? The origin of anything lies in the interactions of multiple causes. In practice, in order to explain the origin of a storm, or anything else, both the person providing the explanation and the one on the receiving end must have a lot of knowledge in common, covering many different areas. Unfortunately, it may not be present.
    You might be an English teacher, an accountant, a housewife, a psychologist, a merchant, a builder, a banker or a student. The chances are that you will not have come across one or more phrasessuch as ‘saturated solution’ or ‘particle carries a tiny electric charge’. And those phrases are themselves simplifications of concepts with many more associations, and more intellectual depth, than anyone can be expected to generate for themselves.
    You might be a biology teacher, a mathematician, or even a science journalist, with a more extensive mental database in such areas. Even so we’d still have difficulty explaining the origin of storms, because
we
don’t understand it in enough depth. None of us is a meteorologist. And even if we were, we
still
wouldn’t be able to generate enough depth of understanding for you to be able to say, ‘Ah, yes – I understand that now.’ Jack is an embryologist, and understands eggs and acorns in some depth; he would have the same problem for the same reason, even for those examples. The origin of absolutely anything on Roundworld – of it, off it, all the way up to everything that exists – is a complicated mesh involving enormously many factors that we know very little about.
    One way to duck out of this issue is to appeal to divine creation. If you believe in a creator god, you can invoke supernatural intervention to explain the origins of anything, from the universe to thunderstorms. Thor does a great job with his hammer: job done, thunder explained. Or don’t you think so? We don’t find that a very satisfactory explanation, because you then have to explain how the gods came to be, and where their powers came from. Maybe it’s not Thor at all, but Jupiter. Maybe it’s a giant invisible snake thrashing its coils. Maybe it’s an