Science of Discworld III

of them,’ said Ponder Stibbons.
    ‘Here? Did we look? We wouldn’t find any anyway, would we?’ said Ridcully. ‘They’d show up as natural forces.’
    ‘But how could they exist here? All those things work by themselves here!’
    ‘Same way we did?’ said Rincewind. ‘And they’ll meddle with anything. You know them. And they really, really hate people …’
    Auditors: personifications of things that have no personality that can be imagined. Wind and rain are animate, and thus have gods. But the personification of gravity, for example, is an Auditor or, rather Auditors. In universes that run on narrativium rather than automatic, they are the means by which the most basic things happen.
    Auditors are not only unimaginative, they find it impossible to imagine what imagination is.
    They are never found in groups of less than three, at least for long. In ones and twos they quickly develop personality traits that make them different , which to them is fatal. For an Auditor to have an opinion that differs from that of its colleagues is certain … cessation. But while individual Auditors cannot hold an opinion (because that would make them individual), Auditors as a whole certainly can, and with grim certainty they hold that the multiverse would be a lot better off with no life in it. Life gets in the way, tends to be messy, acts unpredictably and reverses entropy.
    Life, they believe, is an unwanted by-product. The multiverse would be more reliable if there wasn’t any. Unfortunately, there are rules. Gravity is not allowed to increase a millionfold and laminate all local life forms to the bedrock, highly desirable though that would appear to be. Simply mugging life forms merely walking, flying, swimming or oozing past would attract attention from higher authority, which Auditors dread.
    They are weak, not very clever and always afraid. But they can be subtle. And the wonderful thing about intelligent life, they have discovered, is that with some care it can be persuaded to destroy itself .

SIXTEEN
MANIFEST DESTINY
    T HE WIZARDS ARE DISCOVERING THAT changing history is not so easy, even when you’ve got a time machine. The Auditors aren’t helping, but history has its own metaphorical Auditor, often called ‘historical inertia’. Inertia is the innate tendency of moving objects to continue moving along much the same track, even if you try to divert them; it is a consequence of Newton’s laws of motion. Historical inertia has a similar effect but a different cause: changing a single historical event, however important it may appear, may have no significant effect on the social context that directs the path of history.
    Imagine we’ve got a time machine, and go back to the past. Not too far, just to the assassination of Abraham Lincoln. In our history, the President lived till the following morning, so a tiny deflection of the assassin’s bullet could make all the difference. So we arrange a small deflection, and he is hit but recovers, with no noticeable brain damage. He cuts a couple of appointments while he recuperates, and then he goes on to do … what?
    We don’t know anything about that new version of history.
    Or do we? Of course we do. He doesn’t turn into a hippopotamus, for a start, or a Ford Model T. Or disappear. He goes on being President Abraham Lincoln, hedged in by all the political expediencies and impossibilities that existed in our version of history and still exist in his .
    The counterfactual 1 scenario of a live Lincoln raises many questions. How much do you think being the American President is like driving a car, going where you want to? Or sitting in a train, observing the terrain that others drive you through?
    Somewhere in between, no doubt.
    Ordinarily, we don’t have to think much about counterfactuals, precisely because they are contrary to fact. But mathematicians think about them all the time – ‘if what I think happens is wrong, what can I deduce that might prove it wrong?’ Any consideration of phase spaces automatically gets tangled up in worlds of if. You don’t really understand history unless you can take a stab at what might have happened if some major historical event had not occurred. That’s a good way to appreciate the significance of that event, for a start.
    In that spirit, let’s think about that altered ‘now’: the beginning of the West’s third millennium of history, but without Lincoln having been assassinated in its past. What would