Time Travel. James Gleick

with the proposition that you or I can go from New York to Pekin without moving farther than our own front door?”

      • The time traveler would surely bump into things. Example: Let’s say he leaves his workshop for a future date, January 1, 1920. While he’s gone, his abandoned wife sells the house. It is torn down. Bricks are heaped where the workshop stood. “But where, oh where, is the traveler? If he remains in the same place, he is surely beneath the ton of bricks and so is his precious machine … This, we aver, is most uncomfortable for the tourist. He is fairly interpenetrated with bricks.”

      • Looked at from an astronomical point of view, celestial motion must be considered as well. “The traveler who moves only in time and not at all in space would suddenly find himself strangling in the empty ether, while the earth went hurtling away from beneath him.”

      Impossible, concludes the philosopher. No one can travel into the future or the past on Mr. Wells’s time machine. We must find other ways of dealing with past and future, every day of our lives.

      WE NEED NOT DEFEND Mr. Wells, because he never meant to promulgate a new theory of physics. He didn’t believe in time travel. The time machine was the handwaving—the pixie dust that helps the willing reader suspend disbelief and get through the story. (See handwavium, n.) It was sheer coincidence that the Time Traveller’s mumbo-jumbo tracked so well with a revolutionary view of spacetime that emerged in physics a decade later. Except, of course, that it was no coincidence at all.

      Wells worked hard to make the handwaving plausible. This first technology of time travel ended up being fairly robust. In fact, he anticipated Pitkin’s semiscientific objections and some others as well. For example, it is the Medical Man who says that space differs from time in that we move freely through one but not the other.

      “Are you so sure we can move freely in space?” the Time Traveller retorts. “Right and left we can go, backward and forward freely enough … But how about up and down? Gravitation limits us there.” That was more true, of course, in the nineteenth century than in the twenty-first. Now we’re used to whizzing about in all three of our dimensions, but space travel (as we might call it) used to be more constrained. Railroads and bicycles were new. So were elevators and balloons. “Before the balloon,” says the Time Traveller, “save for spasmodic jumping and the inequalities of the surface, man had no freedom of vertical movement.” What the balloon does for the third dimension, the time machine might do for the fourth.

      Our hero presents his miniature prototype time machine as an amalgam of science and magic: “You will notice that it looks singularly askew, and that there is an odd twinkling appearance about this bar, as though it was in some way unreal.” A turn of the tiny lever sends the gizmo into the void with a puff of wind. Now Wells anticipates the next objection from the realists. If the time machine has gone back to the past, why had they not seen it en route (as it were) when they were in the room last Thursday? And if into the future, why is it not still visible, passing through each successive moment? The explanation comes in ersatz psychological jargon. “It’s presentation below the threshold,” says the Time Traveller, nodding to the Psychologist. “You know, diluted presentation.” The same reason you can’t see the spokes of a spinning bicycle wheel or a bullet whizzing through the air. (“Of course,” the Psychologist replies. “I should have thought of it.”)

      Wells likewise foresaw the objection of the Philosopher that the traveler risked crashing through piles of bricks and other unexpected alterations in the landscape. “So long as I travelled at a high velocity through time, this scarcely mattered; I was, so to speak, attenuated—was slipping like a vapour through the interstices of intervening substances!” Simple, when you put it that way. Halting in the wrong place, however, would still be dangerous. And exciting.

      To come to a stop involved the jamming of myself, molecule by molecule, into whatever lay in my way; meant bringing my atoms into such intimate contact with those of the obstacle that a profound chemical reaction—possibly a far-reaching explosion—would result, and blow myself and my apparatus out of all possible dimensions—into the Unknown.

      Wells laid down the rules, and from then on all the world’s time travelers would have to obey. Or if not obey, at least explain. Jack Finney put it this way in a time-travel story in the Saturday Evening Post, 1962: “There’s a danger a man might appear in a time and place already occupied … He’d be all mixed in with the other molecules, which would be unpleasant and confining.” Explosions are ever popular. Philip K. Dick in 1974: “… the hazard in re-entry of being out of phase spatially and colliding right down to the molecular level with two tangent objects … You know, ‘No two objects can occupy the same space at the same time.’” At last, the perfect corollary of “Nobody can be in two places at once.”

      Wells never did justify treating the earth as a fixed point of the cosmos. Nor for that matter did he worry about where the Time Machine gets the energy to power its voyages. Here, too, he established a tradition. Even a bicycle needs someone to pedal, but time machines have unlimited free fuel, by the universe’s grace.

      WE’VE HAD A CENTURY to think about it, and we still need to remind ourselves every so often that time travel is not real. It’s an impossibility, just as William Gibson suspected—a magic on the order of kissing one’s own elbow. But when I say that to a certain well-known theoretical physicist, he gives me a pitying look. Time travel is no problem, he says. At least if you want to travel to the future.

      Oh, well, sure—you mean we’re all traveling forward in time anyway?

      No, says the physicist, not just that. Time travel is easy! Einstein showed us how to do it. All we have to do is approach a black hole and accelerate to near the speed of light. Then, welcome to the future.

      His point is that acceleration and gravitation both slow the clocks, relativistically, so you could age a year or two on a spaceship and return home a century hence to marry your great-grandniece (as Tom Bartlett does in Robert Heinlein’s 1956 novel Time for the Stars). This is proven. GPS satellites have to compensate for relativistic effects in their very exact calculations. It’s hardly time travel, though. It is time dilation (per Einstein, Zeitdilatation). It’s an antiaging device.^fn2 And it’s a one-way street. There’s no going back to the past. Unless you can find a wormhole.

      “Wormhole” is John Archibald Wheeler’s word for a shortcut through the warped fabric of spacetime—a “handle” of multiply connected space. Every few years someone makes headlines by hailing the possibility of time travel through a wormhole—a traversable wormhole, or maybe even a “macroscopic ultrastatic spherically-symmetric long-throated traversable wormhole.” I believe that these physicists have been unwittingly conditioned by a century of science fiction. They’ve read the same stories, grown up in the same culture as the rest of us. Time travel is in their bones.

      We have arrived at a moment of cultural history when the doubters and naysayers are the real practitioners of time travel, the science-fiction writers themselves. “Totally impossible on theoretical grounds,” declared Isaac Asimov in 1986. He didn’t even bother to hedge his bets.

      It can’t and won’t be done. (If you’re one of those romantics who thinks nothing is impossible, I won’t argue the case, but I trust you won’t decide to hold your breath until such a machine is built.)

      Kingsley Amis, assessing the literary culture of science fiction in 1960, felt he was stating the obvious when he said, “Time travel, for instance, is inconceivable.” Thus practitioners of the genre resort to some version of Wells’s hand-waving explanation—“an apparatus of pseudo-logic”—or, as time goes on, simply trust their readers to suspend disbelief. And so it’s the science-fiction writers who remain willing to treat the future as open, while all around them physicists and philosophers surrender to determinism. “One is grateful that we have a form of writing which is interested in the future,” said Amis, “which is ready to treat as variables what are usually taken to be constants.”

      As for Wells himself, he continued to disappoint his believers.^fn3 “The reader got a fine confused sense of immense and different things,” he said in 1938. “The effect