What Time Is It There?

••• Cosmic Profs Beat The Clock

The century-old dream of time travel remains one of our greatest control fantasies—irrational and irresistible, supremely conducive to megalomania, born of morbid curiosity and mortal dread. Barring the odd literary anachronism (Rip Van Winkle's big-sleep displacement, the Connecticut Yankee's Camelot stopover), it wasn't until 1895, when H.G. Wells unveiled The Time Machine, that the concept crystallized in the public consciousness, spanning nuts-and-bolts mechanics to abstruse metaphysics.

Wells constructed a launch pad for countless time-warp scenarios: destiny-tweaking second chances, prescience-exploiting schemes, cautionary dispatches from dystopian futures. The more enterprising fictions emphasized solipsistic absurdities. Via several carefully scheduled temporal hops (not to mention gender reassignment surgery and a disturbingly literal twist on Narcissus), the young man in Robert Heinlein's short story "All You Zombies—" turns out to be his own father andmother—and the bartender to whom he's confiding the whole sorry tale. Time travel went on to colonize our common dreams: in Harlequin romances, in the cathode memory banks of Star Trekand Dr. Who, and of course, at the movies, where time is lost and regained as a matter of course, and where beat-the-clock escapades have ranged from Chris Marker's death-haunted curio, La Jetée, to Hollywood franchises by Robert Zemeckis and James Cameron.

Is theory finally catching up with fantasy? Consigned to sci-fi imaginations for much of the 20th century, time travel has emerged as a legitimate field of scientific inquiry in the last decade, bolstered by the Stephen Hawking-led pop-science boom. "In some senses, it's still a bit wacky, but there's definitely a respectable side," says Paul Davies, professor of natural philosophy at Macquarie University in Sydney and author of the brazenly titled new book How to Build a Time Machine(Viking). "There's a cottage industry of physicists who study time travel, not in the sense of patenting a design for a time machine but of trying to understand the causal structure of the universe."

Ronald Mallett, a professor of theoretical physics at the University of Connecticut, has harbored an interest in the field since he was a young boy. "My father died of a heart attack when I was 10, and not long after that I read The Time Machine," he says. "I thought if I could build a time machine, I could go back and warn him." But as a physicist, Mallett didn't even contemplate time travel research for years: "In many ways it was a conservative field, and I didn't want to be considered a nutcase."

There's little danger of that now. Just as almost every sci-fi author has dusted off a time machine at some point, most big-name physicists (even the skeptical ones) have published papers in leading journals exploring the theoretical possibilities of time travel. (The worlds collide in Gregory Benford's 1980 novel Timescape, with real-life members of the physics community scrambling to send a message into the past to avert an ecological disaster—Davies and some of his colleagues show up as characters.)

Wells himself studied biology, though he never claimed to be more than an amateur scientist. The Time Machinewas conceived mainly as philosophical and social commentary, but its scientific insights are not to be underestimated. The culmination of a Victorian obsession with higher dimensions that also encompassed Edwin Abbott's mathematical brainteaser, Flatland, Wells's first novel hypothesized time as the fourth dimension a full decade before Einstein described a space-time continuum in his special theory of relativity. Which is not to say that Wells's contraption is in any way a feasible archetype. His Time Traveller leaps into a quartz-lined carriage, cranks a lever, and hurtles through the time dimension while remaining fixed in the three dimensions of space—"fast-forwarding a cosmic movie," as Davies puts it.

But in Einstein's unified space-time, it's impossible to move in time without also moving in space. (Cher's linkage of chrono-manipulation—viz., "if I could turn back time"—with interstellar travel—to wit, "if I could reach the stars"—is, in at least one regard, scientifically sounder than Wells's invention.) What's more, the notion of an absolute landmark in space is meaningless, given the Earth's orbit around the Sun, and the orbit of the solar system around the center of the galaxy. Paul J. Nahin, author of Time Machines, an extensive survey of time travel in science and science fiction, also notes that a Wellsian machine, which never gets out of its own way, runs the risk of colliding with itself.

Given the unyielding laws of physics, it may come as a surprise that travel into the future—or at least a restricted form thereof—is a proven fact. Einstein shattered Newton's view of absolute time, "flowing equably without relation to anything external," by identifying a "time dilation" effect. Time is stretched by motion, Einstein theorized, and moving objects age more slowly. On a high-speed trip, clocks tick slower: An astronaut's wristwatch and biological clock, like his pulse rate, would slow down relative to someone who remains on Earth. The net effect is that he gains time on his journey. The higher the velocity, the greater the dilation factor. Consider an example given in Davies's book: A round-trip flight to a star 10 light-years away at almost the speed of light (180,000 miles per second) would take just over 20 Earth years, but the astronaut would age less than three years on the trip, so upon her return, she has effectively traveled 17 years into the future.

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