Taming time travelThis sounds to me like another version of Niven's Law, which is kind of old news. Still, it's interesting to have physicists discussing it, not just science fiction writers.
New work solves paradoxes by making the impossible impossible
By Laura Sanders (Science News)
Web edition : Tuesday, July 20th, 2010
Novelists and screenwriters know that time travel can be accomplished in all sorts of ways: a supercharged DeLorean, Hermione’s small watch and, most recently, a spacetime-bending hot tub have allowed fictional heroes to jump between past and future.
But physicists know that time travel is more than just a compelling plot device — it’s a serious prediction of Einstein’s general relativity equations. In a new study posted online July 15, researchers led by Seth Lloyd at MIT analyze how some of the quirks and peculiarities of real-life time travel might play out. This particular kind of time travel evades some of its most paradoxical predictions, Lloyd says.
Any theory of time travel has to confront the devastating “grandfather paradox,” in which a traveler jumps back in time and kills his grandfather, which prevents his own existence, which then prevents the murder in the first place, and so on.
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In contrast, Lloyd prefers a model of time travel that explicitly forbids these inconsistencies. This version, posted at arXiv.org, is called a post-selected model. By going back and outlawing any events that would later prove paradoxical in the future, this theory gets rid of the uncomfortable idea that a time traveler could prevent his own existence. “In our version of time travel, paradoxical situations are censored,” Lloyd says.
But this dictum against paradoxical events causes possible but unlikely events to happen more frequently. “If you make a slight change in the initial conditions, the paradoxical situation won’t happen. That looks like a good thing, but what it means is that if you’re very near the paradoxical condition, then slight differences will be extremely amplified,” says Charles Bennett of IBM’s Watson Research Center in Yorktown Heights, N.Y.
For instance, a bullet-maker would be inordinately more likely to produce a defective bullet if that very bullet was going to be used later to kill a time traveler’s grandfather, or the gun would misfire, or “some little quantum fluctuation has to whisk the bullet away at the last moment,” Lloyd says. In this version of time travel, the grandfather, he says, is “a tough guy to kill.”
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(Via Ray Kurzweil's Daily Newsletter.)
More on time travel here (and follow the links) and here.
