The Science of Discworld IV Judgement Da - By Terry Pratchett, Ian Stewart Page 0,8

as big ones.

The discovery of the Higgs exemplifies some basic issues about how scientists view the world, and about the nature of scientific knowledge. The actual evidence for the Higgs is a tiny bump on a statistical graph. In what sense can we be confident that the bump actually represents a new particle? The answer is extremely technical. It is impossible to observe a Higgs boson directly, because it splits spontaneously and very rapidly into a swarm of other particles. These collide with yet other particles, creating a huge mess. It takes very clever mathematics, and very fast computers, to tease out of this mess the characteristic signature of a Higgs boson. In order to be sure that what you’ve seen isn’t just coincidence, you need to observe a large number of these Higgs-like events. Since they are very rare, you need to run the experiments many times and perform some sophisticated statistical analysis. Only when the chance of that bump being coincidence falls below one in a million do physicists allow themselves to express confidence that the Higgs is real.

We say ‘the’ Higgs, but there are alternative theories with more than one Higgs-like particle – eighteen fundamental particles. Or nineteen, or twenty. But now we know there is at least one, when before it might have been none.

Understanding all this requires considerable expertise in esoteric areas of theoretical physics and mathematics. Even understanding the aspect of ‘mass’ involved, and which particles it applies to, is complicated. Performing the experiment successfully requires a range of engineering skills, in addition to a deep background in experimental physics. Even the word ‘particle’ has a technical meaning, nothing like the comfortable image of a tiny ball bearing. So in what sense can scientists claim to ‘know’ how the universe behaves, on such a small scale that no human can perceive it directly? It’s not like looking through a telescope and seeing that Jupiter has four smaller bodies going round it, as Galileo did; or like looking down a microscope and realising that living things are made from tiny cells, as Robert Hooke did. The evidence for the Higgs, like that for most basic aspects of science, is not exactly in your face.

To come to grips with these questions, we take a look at the nature of scientific knowledge, using more familiar examples than the Higgs. Then we distinguish two fundamentally different ways to think about the world, which will form a running theme throughout the book.

Science is often thought to be a collection of ‘facts’, which make unequivocal statements about the world. The Earth goes round the Sun. Prisms separate light into its component colours. If it quacks and waddles, it’s a duck. Learn the facts, master the technical jargon (here being: orbit, spectrum, Anatidae), tick the boxes, and you understand science. Government administrators in charge of education often take this view, because they can count the ticks (Ixodidae – no, scratch that).

Oddly, the people who disagree most strongly are scientists. They know that science is nothing of the kind. There are no hard-and-fast facts. Every scientific statement is provisional. Politicians hate this. How can anyone trust scientists? If new evidence comes along, they change their minds.

Of course, some parts of science are less provisional than others. No scientist expects the accepted description of the shape of the Earth to change overnight from round to flat. But they have already seen it change from a plane to a sphere, from a sphere to a spheroid flattened at the poles, and from a perfect spheroid to a bumpy one. A recent press release announced that the Earth is shaped like a lumpy potato.fn2 On the other hand, no one would be surprised if new measurements revealed that the Earth’s seventeenth spherical harmonic – one component of the mathematical description of its shape – needed to be increased by two per cent. Most changes in science are gradual and progressive, and they don’t affect the big picture.

Sometimes, however, the scientific worldview changes radically. Four elements became 98 (now 118 as we’ve learned how to make new ones). Newton’s gravity, a force acting mysteriously at a distance, morphed into Einstein’s curved spacetime. Fundamental particles such as the electron changed from tiny hard spheres to probability waves, and are now considered to be localised excitations in a quantum field. The field is a sea of particles and the particles are isolated waves in that sea. The Higgs field is an example: here the corresponding particles are Higgs