A brief history of time travel

In this context, dates are possibly irrelevant, or even misleading. But if we stick for the moment with conventional calendars, then we can tentatively suggest that time travel began precisely 100 years ago, in January 1895, with the publication o f H G Wells's The Time Machine.

Before that - again, let's hang on to before and after for the purposes of argument - there had been a few fictional attempts at peering into the past or the future: Mark Twain's A Connecticut Yankee at the Court of King Arthur, for instance, had its hero transported backwards through time after being hit on the head; in William Morris's News from Nowhere, the protagonist dreamt himself forward 100 years; and the Rip Van Winkle-type story, in which a sleeper awakes after the passage of years to see what's been happening to society, was common enough (Wells himself dabbled in the genre a few years later, in When the Sleeper Awakes). But the notion of moving freely backwards and forwards in time, in the same way that we can move about in space, that was something new.

Times change, though: these days, at least in terms of cinema and television, time travel is as common as stepping on the bus, or more so. After all, the bus movie is still an under represented genre (Speed is the only recent example that comes to mind),while time travel is burgeoning; Back to the Future Parts I, II and III, Terminator and Terminator 2, the television series Quantum Leap and the Jean-Claude Van Damme vehicle Timecop. Each of these has its own idea of how time travel might work - the 88miles-an-hour DeLorean in Back to the Future, Sam Beckett's out-of-body jaunting in Quantum Leap - but they are all recognisably descended from Wells's central idea. This is, as his anonymous Time Traveller puts it: "There is no difference between Time and any of the three dimensions of space except that our consciousness moves along it."

At the time, this view of time as the fourth dimension was novel - indeed, you could take it as prophetic, anticipating Einstein's concept of spacetime. Wells's Time Traveller explains his theory by flourishing portraits of a man at different stages in his life: "All these are evidently sections, as it were, Three-Dimensional representations of his Four-Dimensioned being . . ." Compare that with this summary of Einstein's picture of spacetime in Peter Coveney and Roger Highfield's book The A

r row of Time (1990): "Thus a human body would appear as a four-dimensional `worm' on the spacetime landscape, each three-dimensional slice of which corresponds to that body at a particular moment in time." In both cases, the idea is that a person at thep resent moment is just a cross-section of his entire being as it is extended through time.

But while Wells was in some respects ahead of his time, in other ways he was still rooted in the past. The kind of time he described was essentially Newtonian - in Newton's universe there is a fixed, unequivocal now which extends across creation, so tha

t it makes sense to talk of events separated by vast distances taking place simultaneously. The flow of time is as fixed and stable as a road; if you only knew how, you could drive up and down it as if it were a motorway. Einstein tore up that picture: in his universe, time is relative and now is a fluctuating concept, varying with the relative speed and position of observer and observed. Time travel is, in this world, theoretically possible; but it couldn't be as simple and direct as Wells envisaged.

Time has seen Einstein's model superseded by the dismayingly complex vision of quantum mechanics, but popular time-travelling fiction has still stuck with Wells's in-between world. Some aspects of Einstein's ideas have taken root: time dilation, a slowi

n g-down of time at high speeds, took Charlton Heston to the future in Planet of the Apes, and elsewhere time travel seems to have become vaguely associated with high acceleration (the Back to the Future series and Timecop both make use of this). But Well

s 's vision remains the culturally dominant one.

It has been altered over time. While Wells broke the mould of time-travelling fiction with his four- dimensional machine, he was still in thrall to some of its mores. The Time Machine is, just as much as News from Nowhere or Edward Bellamy's Looking Backward , a work of social criticism, using the future to comment on the present - the cannibalistic Morlocks of his future are clearly the last stage in the evolution of capitalism. Now is necessarily a fixed point which can be measured up against other eras. For the modern time traveller, though, the present is as malleable as the future; his constan

t preoccupation is messing around with history.

In Back to the Future this is seen as a good thing - Michael J Fox manages to turn his dad from downtrodden wimp into successful businessman; Quantum Leap treats the notion more seriously, but still makes time travel a philanthropic enterprise. Timecop is more ambivalent; Jean-Claude Van Damme's job is to stop villains messing with history, but it turns out that you can change history in positive ways too.

Time after time, physicists come up with new ideas about how time travel might work - the American Kip Thorne and his colleagues have recently publicised the idea of "wormholes" in space, through which we could observe past events. Most serious versions of time travel come with built-in disadvantages, though. Some of the more exotic forms of quantum mechanics would allow time travel, for instance, but journey's end would be in a different universe; more conventional ideas involve the traveller accelerating with an energy equivalent to the mass of the entire universe, which is hardly fuel-efficient.

But it's probably fair to say that most scientists regard this sort of hypothesising as a waste of time, if only because fiddling with history creates irresolvable paradoxes - the fundamental one being that if the time traveller changes the past, he changes the conditions that sent him back in time in the first place.

Popular fiction likes to have a good time with these contradictions - as when Michael J Fox flirts with his mother - but usually ends up by dodging them. In Terminator, for example, the time-travelling androids don't change history, they help to fulfil it. When efforts are made to sort out paradoxes, the results are generally unhappy: Timecop has many virtues, but as history gets switched backwards and forwards the plot becomes not just unfathomable but utterly impervious to logic. The usual

l y sensitive and intelligent Quantum Leap decended into tasteless bathos when it came up against real life - Sam failed to prevent the Kennedy assassination, but it turned out that the first time around Jackie was killed too, and we'd all forgotten.

Time travel doesn't have much to do with science or logic these days, it seems: instead, its mechanisms are determined by American ideals of self-determination and the pursuit of happiness. As Doc Brown tells Marty McFly at the end of Back to the Future Part III, "your future hasn't been written yet. No one's has. Your future is whatever you make it". H G Wells and the decline of civilisation seem a very long time ago. You wonder, what would he make of it all if he were around today? It may y et happen.