The Science of Discworld IV

Higgs is a small bump on an otherwise smooth curve. With the mind-set and traditions of particle physics, it is interpreted as a particle. What’s interesting to us is how the bump becomes the object of attention, while the much larger quantity of data representing the smooth curve is relegated to the background.
    A more familiar example has the same features. Our view of the solar system, with all the planets, all the asteroids and comets, behaving as they should, would be upset if we spotted a spaceship rocketing about but thought it was just another regular body. It would be a malefactor, not obeying the law of gravity. Indeed, the law tells us what is natural, so the spaceship becomes an anomaly.
    Think of all the fuss about the Pioneer anomaly, an unexplained deceleration discovered when observing the spacecraft Pioneer 10 and Pioneer 11. These were the first space probes to reach the outer planets of the solar system, from Jupiter to Neptune. Because of the gravitational pull of the Sun, their speed continually decreased, but they were travelling fast enough to escape the solar system entirely, given enough time. However, when they were at about the same distance from the Sun as Uranus, observations showed that they were slowing down a little bit faster than gravity alone could explain – by about one billionth of a metre per second per second. After much head-scratching, an analysis published in 2011 showed that this effect could be accounted for by the way the craft were radiating heat, which created very small pressure effects.
    Here, the underlying physical law, that of gravity, sets up the scenery: the backdrop against which the spaceship becomes a story.
Pan narrans
cannot help but see the spaceship as the most interesting item, because it doesn’t fit the story – it seems not to obey the law.
    Our minds seem to have evolved to place extra weight on exceptions. The prolific science fiction and popular science author Isaac Asimov wrote: ‘The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka” but “That’s funny …”’ Law-abiding planets and comets are banal, unable to catch ourattention. In the same way, we find the law-abiding mass of humanity essentially boring, so our stories are about witches and malefactors. Among Discworld’s characters, the witch Granny Weatherwax and the sweeper and history monk Lu-Tze catch our attention. It’s the
exceptions
to the law that make the law useful.
    Are laws like that of gravity unique, special statements that are in some sense universally true? Would aliens come up with a theory like gravity, or is there something peculiarly human about falling apples, which leads our peculiar minds on to lunar orbits and solar systems? Is there perhaps a quite different way to describe solar systems?
    Similarly, when Thomson started playing with cathode ray tubes, he had no idea that he was separating a beam of electrons, breaking up atoms. If we had started from some
other
particle than an electron, and we had gone on to find a zoo of others, would we have described the same zoo? Or would we have come up with a different zoo, which nevertheless describes the ‘real world’ as accurately as the one we’ve got?
    Physicists, by and large, think not; they believe that there really
are
these particles out there, and that any scientific endeavour would find the same zoo. But the zoo you find depends on the theoretical model you use to direct the search. Ten years ago they had a different zoo, and in ten years’ time …
    To expand on that point, consider the development of quantum mechanics. The relevant law here is the Schrödinger equation, which describes the state of a quantum system as a propagating wave. However, it seems to be impossible to detect this wave, as such, experimentally. Observations of a quantum system give specific results, and once you’ve made one observation, you’ve interfered with the hypothetical wave. So you can’t be sure that the next observation refers to the same wave. This apparently inherent indeterminacy has led to some extra interpretational features of the theory: that the quantum wave is a wave of probabilities, telling us what the state might be, and how likely any given choice is, but not what the state
is
;that measurements ‘collapse’ the wavefunction to a single state, and so on. By now this interpretation has become close to received gospel, and attempts to find