The Science of Discworld Revised Edition by Terry Pratchett

universes evolve? A remarkable feature of our universe is the presence of Black Holes. These are regions of space-time that contain so much mass that light (and matter) cannot get out; they are formed by the collapse of massive stars. It used to be thought that Black Holes are rare, but now they seem to be showing up all over the place, in particular at the cores of most galaxies. Theoretical work shows that the constants of our universe are unusually good for making Black Holes.
    Why? Smolin argues that each Black Hole in our universe is in effect a doorway to an adjacent universe, but because nothing can come out of a Black Hole we cannot know what its on the far side of that door. In particular, the adjacent universe might have different fundamental constants compared to ours. So universes could ‘breed’ by budding off baby universes through Black Holes, and natural selection would favour those that had the most offspring – whose constants would automatically be unusually good for making Black Holes. So maybe we live in one of those babies.
    There are some difficulties with this theory. In particular, how would selection work? How can universes
compete
? But it’s an interesting, if rather wild, idea. And it offers a concrete proposal about how a universe can ‘make up’ its laws: some, at least, could be imposed upon it at birth.
    The Big Bang, then, may have done more than just bringing space and time into being. It may also have brought ‘the’ rules of physics – the ones that now apply to our world – into being. During the becoming of its first moments, our universe kept changing its state, changing the rules it accessed. In this respect it was rather like a flame, which changes its composition according to its own dynamics and the things that it is burning. Flames are all more or less the same shape, but they don’t
inherit
that shape from a ‘parent’. When you set light to a piece of paper, the flame builds itself from scratch using the rules of the outside universe.
    In the opening instants of the universe, it wasn’t just substances, temperatures and sizes that changed. The rules by which they changed
also
changed. We don’t like to think this way: we want immutable laws, the same
always
. So we look for ‘deeper’ laws to govern how the rules changed. Possibly the universe is ‘really’ governed by these deeper laws. But perhaps it just makes up its own rules as it goes along.
    1 Not while these are still in the polar bear.
    2 This figure replaces the previously favoured value of about 20 billion years. Recently lots of scientists collectively decided it should be 15 billion instead. (For a while some stars seemed to be older than the universe, but the age of those stars has also been downsized.) In other circumstances they might well have settled for 20 billion. If this worries you, substitute the term ‘a very long time’.
    3 Indeed, impeccable Discworld thinking is that no matter how big the universe grows, it’s always the same size.

SEVEN
BEYOND THE FIFTH ELEMENT

    IN THE QUIET of the night, Hex computed. Along its myriad glass tubes, the ants scurried. Crude magic sparkled along cobwebs of fine bronze wire, changing colour as it changed logic states. 1 In the special room next door the beehives, long-term storage, buzzed. The thing that went ‘parp’ did so occasionally. Huge wheels turned, stopped, turned back. And still it wasn’t enough.
    The light of the Project fell across H EX ’s keyboard. Things were happening in there, and H EX did not understand them. And that was taxing, because there
was
something there to understand.
    H EX was largely self-designed, which was why it worked better than most things in the University. It generally tried to develop a responsive way of coming to grips with any new task; the bees had been a particularly good idea, because although the memory retrieval was slow, the total memory increased with time and good apiary practice.
    Now it