Time Travel. James Gleick

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СКАЧАТЬ and t′ and t′′ and yet he would prove once and for all that time is different from space. To wit: we can move hither and yon in space, but not in time. Or rather, we do move in time, but not freely: “a thing moves in time only by moving with all other things.” And how would he prove this? In a most unexpected way:

      To make the proof as simple as possible, I shall present it in the form of a sober criticism of one of the wildest flights of literary fancy which that specialist in wild flights, H. G. Wells, has indulged in. I refer, of course, to his amusing skit, The Time Machine.

      It was the first but not the last time that Mr. Wells’s amusing skit would impose itself upon the attention of this august journal.

      “You cannot leap back into the thirteenth century, nor can a man of that period hop into our own,” wrote Pitkin. “Mr. Wells would have us imagine a man at rest in the space dimensions, but moving with respect to the time of that space field. Very well! Let us do our noblest to play the game. What do we find? Something very disconcerting indeed. Something which, I fear, will make time-touring very unpopular among sedate people.”

      The traveler flies, not through abstract time (like the “pure space” of the geometer). He flies through real time. But real time is history: and history is the course of physical events. It is the sequence of activities, physical, physiological, political, and otherwise.

      Do we really want to go down this road? Must we look for errors of logic in a piece of fantastic fiction?

      Yes, we must. The practitioners of time travel, even in “pulp” magazines, were soon to work out rules and justifications that would make a Talmudist proud. What is allowed, what is possible, what is plausible—the rules evolved and varied, but logic must be honored. We may as well begin with Professor Pitkin, man of many ideas, some of them large, in the Journal of Philosophy.

      His argument would not seem very sophisticated to a typical teenage sci-fi aficionado circa 1970. In fairness, he recognizes that common human intuition about the world often fails to comprehend the strangeness of reality. Science keeps surprising us. Which way is up, for example? “It was held impossible ‘by the very nature of things,’” he notes, “that the earth should be a sphere, with people on the other side walking, heads downward.” (He might have added that Aristotle’s common sense revealed three and no more than three spatial dimensions: “the line has magnitude in one way, the plane in two ways, and the solid in three ways, and beyond these there is no other magnitude because the three are all.”) Could it be, he asks, that time travel merely strikes us as impossible “because of certain prejudices we entertain or certain facts and tricks of which we are still hopelessly ignorant?” Let us be open-minded. “[The] answer, whatever that may be, carries immeasurable consequences for metaphysics.”

      So Pitkin applies the tools of logic. These are his chief points:

      • As the time machine rushes through the years, everything ages rapidly, so the man in the machine should, too. “Nations rise and fall, tempests leap up, destroy, and subside, houses are built with toil and burned in the frenzy of sudden war, and so on.” As for the tourist, his clothes are unruffled and he scarcely ages a day. “How is this possible? If he has passed through a hundred thousand generations, why isn’t he a hundred thousand generations old?” Here is an obvious contradiction: “the first contradiction in the whole proceeding.”

      • Time goes at a certain rate, and this rate must be the same for everyone, everywhere. “Two objects or systems” cannot have “different rates of displacement or change in time”—obviously. Pitkin scarcely knew what devilishness Albert Einstein was conjuring in Berlin.

      • Traveling through time must obey rules of arithmetic, just like traveling through space. Do the math: “To traverse a million years in a few days is exactly like traveling a thousand miles in one inch.” A thousand miles does not equal one inch; ergo, a million years cannot equal a few days. “Now is not this a pure self-contradiction, on a par 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.

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