Time Travel in 'Looper': Dubious, but Not for the Reason You Might Think

Reading the scholarly theories on going back in time—which, by the way, might be possible

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TriStar / Alliance; D. Reidel

TO THE NAKED EYE, IT MAY APPEAR THAT: Looper, the Bruce Willis-Joseph Gordon-Levitt vehicle that opened last weekend, is a pretty nifty film with an impossible, imaginary premise: It's possible to travel back in time and change the past.

BUT ACCORDING TO SOME EXPERTS WHO THOUGHT VERY HARD ABOUT THIS: Looper is definitely unrealistic, but not for the reason we might think. Time travel, as it turns out, may not be impossible at all—it's the alteration of the course of history that's the dubious part.

Yes, activate suspension of disbelief now. But the maybe-viability of time travel has kept logicians, physicists, philosophers, and other academics squabbling among themselves for decades. Several modern theories of time travel are built on Albert Einstein's vision of the universe: a model that imagines a four-dimensional spacetime continuum with a curving shape. Einstein's model, according to University of Connecticut theoretical physicist and aspiring time-machine builder Ron Mallett, allows for the possibility of warps, twists, and manipulations of space and time, which would bend the continuum into a closed loop that would enable time travel. Dr. Mallett explained some of his theories to CNN in 2007:

Mallett's lifelong dream has been to build a time machine in order to go backward in time and tell his father, who died of a heart attack when Mallett was 10, not to smoke. As Mallett points out, though, science is still a long way away from sending an actual person—or even an object or piece of data—to a different point in the future or the past. The discussion of time travel's feasibility rests squarely on the theoretical possibility at this point.

MORE THEORIES, MORE PROBLEMS: Looper, set in a bleak vision of 2044, pits young Joe (Gordon-Levitt), a killer of future criminals sent backwards in time to be executed, against an older version of himself (Willis) who's been exiled to the past. But time travel into the past is where the argument for real time travel becomes the most problematic.

According to the Internet Encyclopedia of Philosophy, the famed theoretical physicist Stephen Hawking and other theorists believe backward causation—a retroactive influence on events that have already happened—may be logically possible, but it's physically impossible. Hawking's belief is that if time travelers could travel back in time, certain forces collectively known as a "Chronology Protection Agency" would prevent him or her from interacting at all with the events of the past.

So at the crux of the time-travel question sits the "grandfather paradox"—the notion that the past cannot be changed because its consequences have already manifested themselves in the future, making it impossible for the time traveler to return "home" to the same future. In 1976, the American philosopher David Lewis explained the grandfather paradox at length in a parable about "Tim" the time-traveler, who travels back to 1921 in his time machine to dispose of his much-hated granddad.

Tim cannot kill Grandfather. Grandfather lived, so to kill him would be to change the past. But the events of a past moment are not subdivisible into temporal parts and therefore cannot change. Either the events of 1921 timelessly do include Tim's killing of Grandfather, or they timelessly don't. We may be tempted to speak of the "original" 1921 that lies in Tim's personal past, many years before his birth, in which Grandfather lived; and of the "new" 1921 in which Tim now finds himself waiting in ambush to kill Grandfather. But if we do speak so, we merely confer two names on one thing. ... If Tim did not kill Grandfather in the "original" 1921, then if he does kill Grandfather in the "new" 1921, he must both kill and not kill Grandfather in 1921—in the one and only 1921, which is both the "new" and the "original" 1921. It is logically impossible that Tim should change the past by killing Grandfather in 1921.

In Looper, young Joe's mission is to kill the elder Joe, while the elder Joe is determined to stay alive and influence the decisions of his younger self. So Looper actually riffs on (and inverts) some variants of the grandfather paradox: the auto-infanticide paradox and the causal loop.

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Ashley Fetters is a former associate editor at The Atlantic.

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