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[44] 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 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?
44
Counterfactuaclass="underline" a more acceptable word for what has for a long time been a very common feature of science fiction, the 'alternate world' or 'worlds of if story (there was a pulp SF magazine in the 1950s called Worlds of If, in fact). 'Counterfactual' is now used when said stories are written by real writers and historians, to save them the indignity of sharing a genre with all those strange sci-fi people.