The Science of Discworld II

the front door. The wizards heard the distant voice of Dee, and then the creak of the stairs.
    â€˜Brethren,’ he said, pushing open the door. ‘There appears to be a visitor for you downstairs.’ He gave them a worried smile. ‘A lady …’

SIXTEEN
FREE WON’T
    W HAT IS THE BIGGEST SOURCE OF DANGER for any organism? Predators? Natural disasters? Fellow organisms of the same species, who constitute the most direct competition for everything? Sibling rivals, who compete even in the same family, the same nest? No.
    The biggest danger is the future.
    If you’ve survived until now, then your past and present offer no dangers, or at least no new dangers. That time you broke your leg and it didn’t heal very well left you vulnerable to lions, but the attack is still going to come, if at all, in the future. You can’t do anything to change your past – unless you’re a wizard – but you can do something to change your future. In fact, everything you do changes your future, in the sense that the nebulous space of future possibilities starts to crystallise out into the one future that actually happens. If you are a wizard, able to visit the past and change that, too, you still have to think about how a range of possibilities crystallises out into just one. You still march forward into your own personal future along your own personal timeline; it’s just that, when seen from the perspective of conventional history, that timeline zigzags a lot.
    We are committed to a view of ourselves as creatures that exist in time, not just in an ever-changing present. That is why we are fascinated by stories of time travel. And by stories about the future. We have established elaborate methods to foretell the future, and find ourselves at the mercy of deep-seated concepts such as Destiny and Free Will, which relate to our place in time and our ability to change thefuture – or not. However, we have an ambivalent attitude to the future. In most respects, we think that it is pre-determined, usually by factors beyond our control. Otherwise, how could it be predicted? Most scientific theories of the universe are deterministic: the laws give rise to only one possible future.
    To be sure, quantum mechanics involves unavoidable elements of chance, at least according to the orthodox attitude of nearly all physicists, but quantum uncertainty fuzzes out and ‘decoheres’ as we move from the microscopic world to the macroscopic one, so on a human scale nearly everything that matters is again deterministic from the physical point of view. That doesn’t mean that we know ahead of time what’s going to happen, though. We have seen that two features of the workings of natural laws, chaos and complexity, imply that deterministic systems need not be predictable in any practical sense. But when we start to think about ourselves, we are utterly certain that we are not deterministic at all. We have free will, we can make choices. We can choose when to get out of bed, what to eat for breakfast, whether or not to put the radio on and listen to the news.
    We’re not so certain that animals have free will. Do cats and dogs make choices? Or are they merely responding to innate and unchangeable ‘drives’? When it comes to simpler organisms like amoebas, we find it difficult to conceive of them choosing between alternatives; though when we watch them through a microscope, we get a strong feeling that they know what they’re doing. We’re happy to believe that this feeling is an illusion, a silly piece of anthropomorphism, investing human qualities in a tiny bag of biochemicals; no doubt the amoeba is responding, deterministically, to chemical gradients in its environment. But it doesn’t look deterministic because of the aforementioned get-outs, chaos and complexity. In contrast, when we make a choice, we have the overwhelming impression that we could have chosen to do something else. If that wasn’t possible, then it wasn’t really a choice.
    We therefore model ourselves as free agents making choice after choice against the background of a complex and chaotic world. We are aware that any threat to our existence – or anything desirable – will come from the future, and that the free choices we make now canand will affect how that future turns out. If only we could foresee the future, we could work out the best choices, and make the future happen the