7 DECEMBER 2006
If you've been to the new Denzel Washington movie Déjà Vu, you probably had the feeling that you'd seen it before. Or at least that you'd seen one very much like it.
There are some similarities to Laura (starring Gene Tierney, 1944). But you're more likely thinking of Timeline (2003), in which mad scientists used quantum teleportation to e-mail whole people back to medieval times. Déjà
Vu is more modest, looking back in time only four days. 
The other difference is that the science in Timeline was absurdly incoherent, whereas Déjà
Vu had a grasp of real physics far beyond the usual Hollywood norm.
Don't get too excited, though. Déjà Vu has many scientific flaws. Still, its basic notions were not dreamed up in science fiction neverland. In fact, they come straight from the pages of the most prestigious physics journals on the planet.
At the core of the Déjà Vu plot is a spacetime tunnel known as a wormhole. In the film, the wormhole allows the FBI to conduct warrantless surveillance on what was going on four days ago, providing a continuous video stream complete with audio. The key question for foiling the bad guy is whether the wormhole is good for more than watching -- that is, whether it's possible for a good guy to travel through it to the past.
Artist's rendition of a futuristic spacecraft approaching
a wormhole. Digital
art by Les Bossinas, from NASA
It's not a new question, of course. Scientists have pondered wormhole travel ever since 1935, when wormholes were first clearly envisioned by Einstein and his collaborator Nathan Rosen. They formulated the equations describing passages between distant points in spacetime, calling them "bridges." (Years later John Wheeler coined the name "wormhole.")
Mathematically, it seemed that wormholes could indeed provide subspace subways, allowing rapid travel between distant points within the universe (or even separate universes). Such tunnels might even connect a point now with a point in the past.
Unfortunately, the math also suggested that traveling through a wormhole subway would not be very much fun, as you would be crushed along the way into subatomic particles.
In 1988, though, Caltech physicist Kip Thorne and collaborators showed that wormhole travel was actually not impossible, as long as you possessed a special form of matter/energy that could prop the hole open. Of course, the properties of this matter were so exotic that it seemed unlikely to exist naturally, and nobody knew how to make any of it.
Then, 10 years later, along came a surprise (the universe is full of them -- surprises, if not wormholes): The universe itself is made mostly of a strange form of invisible energy. This "dark energy" may be just exotic enough to prop open wormholes.
Now the story gets messy. For the last decade, physicists have been arguing about whether dark energy changes the rules enough to make wormhole time travel a serious scientific subject. In the past two years,
about 50 papers have appeared in the online physics archive with "wormhole" in the title. Many of these papers have been published in journals such as Physical Review Letters and Physical Review D.
Some papers contend wormholes will not stay stable very long or identify other reasons why wormholes would turn into dead (literally) ends. Yet some analyses argue that under certain conditions, wormholes big enough to travel through are within the realm of physics. One paper, by Peter Kuhfittig of the math department at the Milwaukee School of Engineering in Wisconsin, finds that wormhole throats of any given size are permissible. "Moreover," he writes in Physical Review D, "various traversability criteria are met, resulting in a wormhole that is traversable for humanoid travelers."
Similar conclusions have been reached by Francisco Lobo of the University of Lisbon.
"These traversable wormhole variations have far-reaching physical and cosmological implications, namely, apart from being used for interstellar shortcuts, an absurdly advanced civilization may convert them into time-machines," he writes in a paper available online.
Some of these papers speculate that wormholes might have been formed shortly after the big bang and remain intact today. The math supporting belief in such wormholes requires some assumptions that may turn out to be wrong, but not any that contradict well-established physics.
"None of the assumptions made in this paper looks too wild, so its results can be regarded as evidence for possibility of natural . . . wormholes," writes Serguei Krasnikov in a paper published this year in Physical Review D. "Obviously the existence of such wormholes would be of enormous significance."
Not that crime fighting a la Déjà Vu will become the latest threat to people's privacy anytime soon. Plenty of physicists still believe that fundamental physics will ultimately prevent wormhole travel from competing with Southwest Airlines and its interstellar descendants. And it's a long jump from finding wormholes in math to finding them in space. Even if wormholes remain permitted by the principles of physics, the technology for using them probably couldn't cope with the practicalities of economics.
But it would not be stupid or silly to suppose that in, say, 1,000 years, society will have become smart enough to expend as much effort on science as it does today on sports. If so, wormhole technology might someday qualify for Reality TV rather than merely popular science fiction. And the good thing is, even if wormhole travel isn't invented until 1,000 years into the future, someone could show up to tell us about it any day now.
E-mail: tsiegfried@nasw.org
