The Science of Discworld Revised Edition

billion kg/cc) – twenty million elephants in a nutshell. They have a surface gravity
seven billion times
that of the Earth, and a magnetic field a trillion times that of the Earth. The particles in a neutron star are so closely packed that in effect it is one big atom.
    Bizarre though they are, some of these superheavy elements may lurk in unusual corners of our universe. In 1968 it was suggested that elements 105–110 could sometimes be observed in cosmic rays – highly energetic particles coming from outer space – but these reports went unconfirmed. It is thought that cosmic rays originate in neutron stars, so maybe in the astonishing conditions found there superheavy elements are formed. What would happen if Population I stars changed by accumulating superheavy stable elements?
    Because the stellar population numbers go III, II, I as time passes – a convention that astrophysicists may yet have cause to regret – we must name these hypothetical stars ‘Population 0’. At any rate, the future universe could easily contain stellar objects quite different from anything we know about today, and as well as novas and supernovas, we might witness even more energetic explosions – hypernovas. There might even be further stages – Population
minus
I and the like. As we’ve said, our universe often seems to make up its rules as it goes along, unlike the rational, stable universe of Discworld.
    1 Silicon might also be able to do this, but nowhere near as readily; if you want other exotic lifeforms you have to start thinking in terms of organized vortices in the upper reaches of a sun, weird quantum assemblages in interstellar plasma, or completely implausible creatures based on non-material concepts such as information, thought, or narrativium. DNA is a different matter entirely: you could surely base lifeforms on other carbon-rich molecules. We can do it now, in laboratories, with minor variants of DNA. See
Evolving the Alien
by Jack Cohen and Ian Stewart.
    2 Ask Mummy or Daddy if you have no idea what we’re talking about.
    3 There also
ought
to be ‘Population III’ stars, older than Population II and consisting entirely of hydrogen and helium. These would explain the occurence of
some
heavy elements in Population II. Howevere, nobody has ever confirmed finding a Population III star, though a whole group of them may have been sighted in 2001, in two tiny red patches in the galaxy cluster Abell 2218. These patches are highly magnified images of the same region of space: the two images, and the magnification, result from gravitational lensing, without which the stars would not have been visible at all. A recent, competing theory removes the need for Population III stars altogether. Instead, very soon after the Big Bang there were heavy elements around, even before any stars formed. So when the first stars condensed, they already were Population II. This contradicts what we say in the main text – lies-to-children, of course.

NINE
EAT HOT NAPHTHA, EVIL DOG!

    THE ROCKS FELL gently together again, and to the annoyance of the Archchancellor they moved in curved lines while doing so.
    ‘Well, I think we’ve proved that a giant turtle made of stone isn’t going to work,’ said the Senior Wrangler, sighing.
    ‘For the tenth time,’ sighed the Lecturer in Recent Runes.
    ‘I
told
you we’d need chelonium,’ said Archchancellor Ridcully.
    Early attempts spun gently a little way away. Small balls, big balls … Some of them even had a mantle of gases, pouring out of the clumsy aggregations of ice and rock. It was as if the new universe had some basic idea of what it ought to be, but it couldn’t quite manage to get a grip.
    After all, the Archchancellor pointed out, once people had something to stand on they’d need something to breathe, wouldn’t they? Atmospheres seemed to turn up on cue. But they were dreadful things, full of stuff not even a troll would suck.
    In the absence of gods, he declared – and a series of simple tests had found no trace of deitygen – it was up to men to get it right.
    The High Energy Magic building was getting crowded now. Even the student wizards were taking an interest, and usually they weren’t even seen during daylight. The Project promised to offer even greater attractions than staying up all night playing with H EX and eating herring and banana pizza.
    More desks had been moved in. The Project was in an expanding circle of instruments and devices, because it