Science of Discworld III

by Terry Pratchett

  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 your morning newspaper be called? Would it be different? Would you still be having much the same breakfast ritual, bacon and eggs and a sausage perhaps? What about the World Wars? Hiroshima?

  A very large number of stories have been written with this kind of theme: Wilson Tucker’s The Lincoln Hunters is set in such an ‘alternat(iv)e universe’ and tackles the Lincoln question.

  Curious things happen in our minds when they are presented with any fictional world. Consider for a moment the London of the late nineteenth century. It did have Jack the Ripper, and we can wonder about the real-world puzzle of who he was. It had Darwin, Huxley and Wallace, too. But it did not have Sherlock Holmes, Dracula, Nicholas Nickleby, or Mr Polly. Nevertheless, some of the best portrayals of the Victorian world are centred around those characters. Sometimes the fictional portrayals are intended to paint a humorous gloss on the society of the period. The Flintstones put just such a gloss on human prehistory, so much so that in order to think rationally about our evolution we must excise all those images, which is probably an impossible task.

  Sherlock Holmes and Mr Polly were Victorians in just the same sense that the tyrannosaur and triceratops in Jurassic Park were dinosaurs. When we envisage Triceratops, we cannot avoid the memory of that warty purple-spotted Jurassic Park skin, as the beast lies on its side, breathing stertorously. And Tyrannosaur, in our mind’s eye, is running after the jeep, bobbing its head like a bird. When we envisage late nineteenth-century Baker Street it’s very difficult not to see Holmes and Watson (probably in one of their filmic versions) hailing a four-wheeler, off to solve another crime. Our pictures of the past are a mixture of real historical figures and scenarios peopled by fictional entities, and it’s difficult to keep them apart, especially as films and TV series acquire better technologies to latch into those spurious pictures in our heads.

  The 1930s philosopher George Herbert Mead made much of the rather obvious point that the present, in a causal world, does not only determine (‘constrain’ if you prefer) the future, it also affects the past, in just this sense: if I discover a new fact about the present, then the (conceptual) past that led up to the new present must also have been different. Mead thereby enabled a rather cute way of seeing how good the portrayals of Sherlock Holmes, or of the Jurassic Park tyrannosaur, are. If my picture of the present isn’t altered at all by the presence or absence of Sherlock Holmes in the 1880s, or if my construction of the present by evolutionary processes isn’t altered at all by seeing Jurassic Park, then these are consistent inventions.

  Dracula and the Flintstones are inconsistent inventions: if they really existed in our past, then the present isn’t what we think it is. Much of the fun of ‘worlds of if’ stories, and of many consistent fictions like The Three Musketeers, is that they show closed-loop causalities in our apparent past. Whether or not D’Artagnan had aggregated the Musketeers and thereby brought into being much of the causal history of seventeenth-century France, children of later centuries would learn the same history in the textbooks. Ultimately, consistent historical fictions make no difference.

  In The Science of Discworld II we played with this idea in several ways: the presence of the Elves was, surprisingly, consistent with our history; stopping them led to stagnation of humans and had to be reversed. In this book the meddling of the Unseen University wizards, in Victorian history this time, is trying to create an apparently internally caused history in which Darwin wrote The Origin of Species and not Theology of Species. We are going to use this trick to illuminate the causalities of human history.

  In order to do this convincingly, we must make the Discworld intrusions consistent, but even then we must address the convergence/divergence problem, which is this. Would such a meddled-with world converge on to ours, demonstrating that history is stable, or would any tiny difference start a divergence that became wider and wider, proving history to be unstable?

  Most people think the latter. Indeed, even the wildly imaginative physicists who believe that a new world history is created by each and every decision in this universe, spawning new universes in which the other choices were implemented, don’t imagine that the histories converge. No, each universe goes its own way, spitting out new and divergent universes as it goes. The Trousers of Time are a tree: their legs can branch but never merge.

  The Worlds of If stories were divided on this issue. Some had each tiny change in the past getting amplified, resulting in vast changes now: we’ve mentioned Bradbury’s story where you trod on a butterfly in the far past, on a dinosaur hunt, and came back to find a fascist regime. Or the changes you made were all wiped out, because there was a gigantic all-powerful inertia-of-events Kismet that you couldn’t change. However you tried to avoid your fate, that only made it more certain to happen. And some stories took a middle way; some things converged and others didn’t.

  This, we think, is the rational way to think about time travel and altering the past.

  After all, we don’t change the rules by which the past works. Gravity still operates, sodium chloride crystals are still cubical, people fall in and out of love, misers hoard and spendthrifts squander. What we change is what physicists call the ‘initial conditions’. We change the positions of a few of the pieces on the Great Chessboard of Life, The Universe and Everything, but we still keep to the rules of chess. That’s how the wizards operated in The Science of Discworld II. They went back in time to remove the Elves from the game board; then they went back again to stop themselves making that mistake.

  We are now ready to think about our question above: would the names of newspapers have changed if Abraham Lincoln had lived to a ripe old age?

  Perhaps some of them would, because some cultures would have become rather different. Perhaps Quebec wouldn’t have been French; perhaps New York would have been Dutch. But names like Daily Mail, Daily News and New York Times are so obvious, so appropriate, that even if the Roman Empire were still running things, the Latin equivalents would seem fitting. Someone would have invented flush toilets, and there would have been a steam engine time, when several people invented steam power. Some things in Western culture seem so likely, from toilet paper on up to (as soon as paper is invented) daily newspapers to plastics to artificial wood … Technology seems to have a set of rules for its advancement, so that it seems rational to expect gramophones of some kind if people make music with musical instruments, then tape players when people get used to electricity and its possibilities for amplification. Then from analogue to digital, to computers … some things seem inevitable.

  Perhaps this feeling is misleading, but it’s silly to insist that absolutely everything in a slightly divergent future has to end up different.

  Organic evolution has lessons for us here, and these lessons can instruct us about how likely various advances in animal organisation were. Innovations like insect wings, vertebrate jaws, photosynthesis, life coming out from the seas on to the land … if we ran evolution on Earth again, would the same things happen? If we went back to the beginning of life on this planet, and killed it, would another system evolve and give us a whole different range of creatures, or would Earth remain lifeless? Or would we be unable to decide whether we’d done anything, because everything would be just the same the second time around?

  If history ‘healed up’, we wouldn’t be able to tell if it was the second, or the hundredth, or the millionth time around – each time sooner or later producing a version of us, whose time machine goes back to The Origin. There would be a consistent time loop, as happened with the Elves in The Science of Discworld II. If life is ‘easy’ to originate (and the evidence does look that way) then this isn’t an exercise in going back and killing your grandfather, or if it is, your grandfather is a vampire and doesn’t remain killed. If life is easy to invent, then preventing it happening once, or a
million times, will make no difference in the long run. The same process that generated it will happen again.

  Looking at the panorama of life on this planet, in time as well as space, we can see that there are two kinds of evolutionary innovation. Photosynthesis, flight, fur, sex, and jointed limbs have all arisen independently in several different lineages. Surely, like toilet paper, we would expect to see them again each time we ran life on Earth. And, presumably, we’ll see them on other aqueous planets when we explore our local region of the galaxy. Such evolutionary attractors, are called ‘universals’, in contrast to ‘parochials’: unlikely innovations that have happened only once in Earth’s history.

  The classic parochial is the curious suite of characters possessed by land vertebrates, because a particular species of Devonian fish succeeded in invading the land in our, real, history. Those fishes’ descendants were amphibians, reptiles, birds, and mammals – including us. Jointed limbs are a universal innovation. The limbs of spiders, hydraulically operated, differ in detail from the limbs of mammals, and were presumably acquired via a different ancestor, perhaps an earlier arthropod proto-spider. The mammalian internal skeleton, with one bone at the body end, then two, then a wrist or ankle, then five lines of bones for fingers or toes, was an independent evolution of the same universal trick.

  This highly unlikely combination now occurs in all land vertebrates (except most of the legless ones), because they are all descended from those fishes that came out of the water to colonise the land. Other parochials are feathers and teeth (of the kind that evolved from scales, which are what we have). And, especially, each of the special body-plans that characterise Earth’s animals and plants: mammal, insect, rotifer, trilobite, squid, conifer, orchid … None of these would appear again after a rerun of Earth’s evolutionary history, nor would we find exact replicas on other aqueous planets.

  We would expect much the same processes to occur, though, in a repeat run of Earth or on another similar world: an atmosphere far from chemical equilibrium as life forms pump up their chemistry using light; planktonic layers of the seas colonised by the larvae of sedentary animals; flying creatures of many kinds. Such ecosystems would also probably have ‘layers’, a hierarchical structure, fundamentally similar to the ecosystems that have emerged in so many different circumstances on Earth. So there would be ‘plantlike’ creatures, a productive majority of the biomass (like Earth’s grass or marine algae). These would be browsed by tiny animals (mites, grasshoppers) and by larger animals (rabbits, antelopes), with a few very large creatures (elephants, whales). Comparable evolutionary histories would lead to the same dramatic scenarios, but performed by different actors.

  The central lesson is that although natural selection has a very varied base to work with (recombinations of ancient mutations, differently assorted in all those ‘waste’ progeny), clear large-scale themes emerge. Marine predators, such as sharks, dolphins, and ichthyosaurs all have much the same shape as barracuda, because hydrodynamic efficiency dictates that streamlining will catch you more prey, more cheaply. Very different lineages of planktonic larvae all have long spines or other extensions of the body to restrain the tendency to fall or rise because their density differs from that of seawater, and most of them pump ions in or out to adjust their densities too. As soon as creatures acquire blood systems, other creatures – leeches, fleas, mosquitoes – develop puncture tools to exploit them, and tiny parasites exploit both the blood as food and the bloodsuckers as postal systems. Examples are malaria, sleeping-sickness, and leishmaniasis in humans, and lots of other parasitic diseases in reptiles, fishes, and octopuses.

  Large-scale themes may be the obvious lesson, but the last examples reveal a more important one: organisms mostly form their own environments, and nearly all of the important context for organisms is other organisms.

  Human social history is like evolutionary history. We like to organise it into stories, but that’s not how it really works. History, too, can be convergent or divergent. It seems quite sensible to believe that small changes mostly get smeared out, or lost in the noise, so that big changes are needed to divert the course of history. But anyone familiar with chaos theory will also expect some tiny differences to set off divergent histories, drifting progressively further away from what might have happened otherwise.

  Changing history is a theme of time-travel stories, and the two issues come together in those stories called ‘worlds of if’.

  We have the strongest feeling that what we do, even what we decide, does change history. If I decide, now, not to go and meet Auntie Janie at the train station even though she’s expecting me because I told her I would … the universe will take a different path from the one it would have taken if I had done the expected. But we’ve just seen that even saving Abraham Lincoln from the assassin would have the tiniest, most local, of effects. Neighbours such as the gas-bag aliens on Jupiter wouldn’t notice Lincoln’s survival at all, or at least not for a very long time. After all, we haven’t yet noticed them.2

  In fact, how will they, or we, notice? How will we be able to say, ‘Just a minute, this newspaper shouldn’t be called the Daily Echo … There must have been a time traveller interfering, so that we’re now in the wrong leg of the Trousers of Time’?

  Auntie Janie making her own way from the station won’t topple empires – unless you believe, with Francis Thompson’s The Mistress of Vision, that

  All things by immortal power

  Near or far

  Hiddenly

  To each other linkéd are

  That thou canst not stir a flower

  Without troubling of a star.

  That is, all contingent chaos butterflies are responsible in some sense for all important events like hurricanes and typhoons – and newspaper titles. When a typhoon, or a newspaper tycoon, topples an empire, that event is caused by everything, all those butterflies, that preceded it. Because change in any one – or perhaps just in one of a very large number – can derail the important event.

  So everything must be caused by everything before it, not just by a thin string of causality.

  We think about causality as a thin string, a linear chain of events, link following link following link … probably because that’s the only way we can hold any kind of causal sequence in our minds. As we’ll see, that’s how we deal with our own memories and intentions, but none of this means that the universe can isolate such a causal string antecedent to any event at all, important or not. And surely ‘important’ or ‘trivial’ is usually human judgement, unless the universe really does ‘smear out’ most small changes (whatever that means), and major events are those whose singular influence can be distinguished at later times.

  Because they are stories, committed to the way our minds work and not to the way the universe works its own causality, most time-travel stories assume that a big (localised) change is needed to have a big effect – kill Napoleon, invade China … or save Lincoln. And time travel stories have another convention, another ‘conceit’, because they are stories, nearer fee-fi-fo-fum than physics. This is the remembered timeline of the traveller. Usually the plot depends on it being unique to him. When he comes back to his present he remembers stepping on the butterfly, or killing his grandfather, or telling Leonardo about submarines … but no one else is conscious of anything other than their ‘altered’ present.

  Let’s move from large events, large or small causes, to how we influence the apparent causality in our own lives. We have invented a very strange oxymoron to describe this: ‘free will’. These words appear prominently on the label of the can of worms called ‘determinism’. In Figments of Reality we titled the free will chapter: ‘We wanted to have a chapter on free will, but we decided not to, so here it is’ in order to expose the paradoxical nature of the whole idea. Dennett’s recent book Freedom Evolves is a very powerful treatment of the same topic. He shows that in regard to ‘free will’ it doesn’t matter whether the universe, including humans, is deterministic. Ev
en if we can do only what we must, there are ways to make the inevitable evitable. Even if it is all butterflies, if tiny differences chaotically determine large historical trends, nevertheless creatures as evolved as us can have ‘the only free will worth having’, according to Dennett. He writes of dodging a baseball coming for his face, and this being perhaps a culmination of a causal chain going right back to the Big Bang – yet if it will help his team, he might let it hit his face.

  But then, what decides it is: will it help his team? That’s not a free choice.

  Inevitable, evitable.

  Dennett’s best example is more ancient: Odysseus’s ship approaching the Sirens. Inevitably, if his men hear the Sirens’ song, they will steer the ship on to the rocks. But the steersman must be able to hear the surf, so there seems no way to avoid their lure. Odysseus has himself lashed to the mast, while all his sailors plug their ears with wax so they cannot hear the Sirens. The vital issue for Dennett is that humans, and on this planet probably only humans, have evolved several stages beyond the observing-and-reacting that even quite advanced animals do. We observed ourselves and others observing, so got more context to embed our behaviour in – including our prospective behaviour. Then we developed a tactic of labelling good and bad imaginary outcomes, just as we labelled our memories with emotional tags. We, and some other apes – perhaps also dolphins, perhaps even some parrots – developed a ‘theory of mind’, a way to imagine ourselves or others in invented scenarios and to anticipate the associated feelings and responses. Then we learned to run more than one scenario: ‘But on the other hand, if we did so-and-so, the lion couldn’t get us anyway …’, and that trick soon became a major part of our survival strategy. So with Odysseus … and fiction … and particularly that dissection of hypothetical alternatives that we call a time-travel story.

  In our minds, we can hold many possible histories, just as Mead showed that every discovery about today implies a different past leading up to it. But whether there is any sense in which the universe has several possible pasts (or futures) is a much more difficult question. We’ve argued that popularisations of quantum indeterminacy, particularly the many-worlds model, have got confused about this. They tell us that the universe branches at every decision point, whereas we think that people have to invent a different mental causal path, a different explanatory history, for each possible present or future.