The Science of Discworld II

states. The spin of an electron, for instance, can either be up or down, a binary choice. The state of the universe is therefore a huge list of ups and downs and more sophisticated quantities of the same general kind: a very long binary message.
    So far, this is a clever and (it turns out) useful way to formalise the mathematics of the quantum world. The next step is more controversial. All that really matters is that message, that list of bits. And what is a message? Information. Conclusion: the real stuff of the universe is raw information. Everything else is made from it according to quantum principles. Ponder would approve.
    Information thereby takes its place in a small pantheon of similar concepts – velocity, energy, momentum – that have made the transition from convenient mathematical fiction to reality. Physicists like to convert their technically most useful mathematical concepts into real things: like Discworld, they reify the abstract. It does no physical harm to ‘project’ the mathematics back into the universe like this, but it may do philosophical harm if you take the result literally. Thanks to a similar process, for example, entirely sane physicists today insist that our universe is merely one of trillions that coexist in a quantum superposition. In one of them you left your house this morning and were hit by a meteorite; in the one in which you’re reading this book, that didn’t happen. ‘Oh, yes,’ they urge: ‘those other universes really do exist . We can do experiments to prove it.’
    Not so.
    Consistency with an experimental result is not a proof, not even a demonstration, that an explanation is valid. The ‘many-worlds’ concept, as it is called, is an interpretation of the experiments, within its own framework. But any experiment has many interpretations, not all of which can be ‘how the universe really does it’. For example, all experiments can be interpreted as ‘God made that happen’, but those selfsame physicists would reject their experiment as a proof of the existence of God. In that they are correct: it’s just one interpretation. Butthen, so are a trillion coexisting universes.
    Quantum states do superpose. Quantum universes can also superpose. But separating them out into classical worlds in which real-life people do real-life things, and saying that those superpose, is nonsense. There isn’t a quantum physicist anywhere in the world that can write down the quantum-mechanical description of a person. How, then, can they claim that their experiment (usually done with a couple of electrons or photons) ‘proves’ that an alternate you was hit by a meteorite in another universe?
    â€˜Information’ began its existence as a human construct, a concept that described certain processes in communication. This was ‘bit from it’, the abstraction of a metaphor from reality, rather than ‘it from bit’, the reconstruction of reality from the metaphor. The metaphor of information has since been extended far beyond its original bounds, often unwisely. Reifying information into the basic substance of the universe is probably even more unwise. Mathematically, it probably does no harm, but Reification Can Damage Your Philosophy.

NINETEEN
LETTER FROM LANCRE
    G RANNY W EATHERWAX, KNOWN TO ALL and not least to herself as Discworld’s most competent witch, was gathering wood in the forests of Lancre, high in the mountains and far from any university at all.
    Wood gathering was a task fraught with danger for an old lady so attractive to narrativium. It was quite hard these days, when gathering firewood, to avoid third sons of kings, young swineherds seeking their destiny and others whose unfolding adventure demanded that they be kind to an old lady who would with a certainty turn out to be a witch, thus proving that smug virtue is its own reward.
    There is only a limited number of times even a kindly disposed person wishes to be carried across a stream that they had, in fact, not particularly desired to cross. These days, she kept a pocket full of small stones and pine cones to discourage that kind of thing.
    She heard the soft sound of hooves behind her and turned with a pine cone raised.
    â€˜I warn you, I’m fed up with you lads always on the ear’ole for three wishes—’ she began.
    Shawn Ogg, astride his official donkey, waved his hands desperately. 1
    â€˜It’s me,