The Science of Discworld Revised Edition

realized some time afterwards, he really ought to have taken into consideration. Nothing excites a magical particle like meeting itself coming the other way.

TWO
SQUASH COURT SCIENCE

    A SQUASH COURT can be used to make things go
much
faster than a small rubber ball …
    On 2 December 1942, in a squash court in the basement of Stagg Field at the University of Chicago, a new technological era came into being. It was a technology born of war, yet one of its consequences was to make war so terrible in prospect that, slowly and hesitantly, war on a global scale became less and less likely. 1 At Stagg Field, the Roman-born physicist Enrico Fermi and his team of scientists achieved the world’s first self-sustaining nuclear chain reaction. From it came the atomic bomb, and later, civilian nuclear power. But there was a far more significant consequence: the dawn of Big Science and a new style of technological change.
    Nobody played squash in the basement of Stagg Field, not while the reactor was in place – but a lot of the people working in the squash court had the same attitudes as Ponder Stibbons … mostly insatiable curiosity, coupled with periods of nagging doubt tinged with a flicker of terror. It was curiosity that started it all and terror that concluded it.
    In 1934, following a lengthy series of discoveries in physics related to the phenomenon of radioactivity, Fermi discovered that interesting things happen when substances are bombarded with ‘slow neutrons’ – subatomic particles emitted by radioactive beryllium, and passed through paraffin to slow them down. Slow neutrons, Fermi discovered, were just what you needed to persuade other elements to emit their own radioactive particles. That looked interesting, so he squirted streams of slow neutrons at everything he could think of, and eventually he tried the then obscure element uranium , up until then mostly used as a source of yellow pigment. By something apparently like alchemy, the uranium turned into something new when the slow neutrons cannoned into it – but Fermi couldn’t work out
what
.
    Four years later three Germans – Otto Hahn, Lise Meitner, and Fritz Strassmann – repeated Fermi’s experiments, and being better chemists, they worked out what had happened to the uranium. Mysteriously, it had turned into barium, krypton, and a small quantity of other stuff. Meitner realized that this process of ‘nuclear fission’ produced energy, by a remarkable method. Everyone knew that chemistry could turn matter into other kinds of matter, but now some of the matter in uranium was being transformed into
energy
, something that nobody had seen before. It so happened that Albert Einstein had already predicted this possibility on theoretical grounds, with his famous formula – an equation which the orangutan Librarian of Unseen University 2 would render as ‘Ook’. 3 Einstein’s formula tells us that the amount of energy ‘contained’ in a given amount of matter is equal to the mass of that matter, multiplied by the speed of light and then multiplied by the speed of light again. As Einstein had immediately noticed, light is so fast it doesn’t even appear to move, so its speed is decidedly big … and the speed multiplied by itself is
huge
. In other words: you can get an awful lot of energy from a tiny bit of matter, if only you can find a way to do it. Now Meitner had worked out the trick.
    A single equation may or may not halve your book sales, but it can change the world completely.
    Hahn, Meitner and Strassmann published their discovery in the British scientific journal
Nature
in January 1939. Nine months later Britain was at war, a war which would be ended by a military application of their discovery. It is ironic that the greatest scientific secret of World War II was given away just before the war began, and it shows how unaware politicians then were of the potential – be it for good or bad – of Big Science. Fermi saw the implications of the
Nature
article immediately, and he called in another top-ranking physicist, Niels Bohr, who came up with a novel twist: the chain reaction. If a particular, rare form of uranium, called uranium-235, was bombarded with slow neutrons, then not only would it split into other elements and release energy – it would also release more neutrons. Which, in turn, would bombard more uranium-235 … The reaction would become self-sustaining, and the potential release of energy would be
gigantic
.
    Would