The Science of Discworld IV Judgement Da - By Terry Pratchett, Ian Stewart Page 0,33

C … The law courts are full of that kind of story, as are most novels, and pretty well all detective stories and science fiction. Even Discworld stories rely on that fictional causality for their coherence. But this is because we are the storytelling ape. A story is a linear sequence of words. It is interesting to speculate whether an advanced alien culture would of necessity concoct such false-to-fact linearly causal stories. Could one always attribute events to three or four, or ten or twenty or a thousand, causes? Or is that the storytelling ape’s way of seeing causality?

If we truly live in a deterministic universe, whatever that means, each successive state is the inevitable result of the immediately preceding state, including such minor causes as the gravitational influences of far stars, even the gravitational influences of the beasts on the planets around far stars. This picture is consistent with certain portrayals of the universe, where for some elements (spaceships approaching the speed of light are favourite candidates) what is in the future for some is on the left for others, while to the right are events-past. So every event is already ‘there’, in some frame of reference. This portrays the whole universe as a vast crystalline structure, with the future just as determinate as the past.

We find this representation as unsatisfactory as the perpetually-dividing Trousers of Time image. Historically, some of it derives from a misreading of Einstein’s concept of a world-line in relativity, a fixed curve running across spacetime and describing the entire history of a particle. One curve, calculated using Einstein’s equations, so one history, right? It’s a valid image in a world with only one particle, whose state can be measured exactly, to infinitely many decimal points. It’s not sensible for the vast, complex universe. If you start drawing a curve in spacetime, and allow it to develop as it grows, at any given stage you may have no idea where it will go next, no way to predict its future path. Einstein’s equations don’t help, because you can’t measure the current state of the universe exactly. That’s not a deterministic universe in any meaningful sense, but after infinite time you’ve got just one curve, one world-line – just as before.

Faced with a choice between two extremes, a world that is random or one that is completely predetermined, most of us dislike both. Neither matches our experiences. That doesn’t prove either of them is wrong, but it makes a key point: any theoretical model must explain our daily experiences. It may well demonstrate that deep down, things are not as we assume; however, it does have to explain how what we assume emerges from the model, even if it’s a misinterpretation of what is ‘really’ happening in the model. For example, the standard claim that science has proved atoms to be mostly empty space does not prove that the apparent solidity of a table is an illusion. You also have to explain why it seems solid to us; then you discover that empty space isn’t empty at all, but filled with quantum fields and forces. Which is what ‘solid’ means at that level of description.

So we would like to find some leeway, some choosable indeterminacy in what happens, if only to foster our illusion of having free will. We would like to think that on an appropriate level of description, what we decide to do is not simply what we have to do.

Worryingly, the great (though sometimes misguided) philosopher René Descartes would have had sympathy with this approach, but that’s because he famously divided the world into two separate aspects, res cogitans and res extensa, mind and matter. He needed res cogitans, the mind, to be freewheeling, so that it could instruct the body, res extensa. In contrast, he thought that little of the body’s influence, if any, went the other way.

Consider the accidents of history that converged on Descartes, making his world a divided one and resulting in all kinds of anomalies in the present intellectual scene, from Arts and Science departments in universities, barely considering each other to be intellectually proper, to descriptions of minds and souls in popular parlance that are, to say the least, irrational.

In Essential Readings in Biosemiotics, Donald Favareau presents a fascinating story that makes a lot of sense. He starts with Aristotle, who wrote some twenty-six essays, only six of which were translated into Latin by Boethius in the sixth century. Two (Categories and On Interpretation) were about the