March 21, 1998|By K. C. Cole | K. C. Cole,LOS ANGELES TIMES

PASADENA, Calif. -- Carl Sagan had a problem. In 1983, the author and astronomer was searching for a rapid interstellar transport system that could whiz the heroine of his science fiction saga, "Contact," billions of miles to the star Vega to meet the newly discovered alien and then return her safely home the next day.

He toyed with the extraordinary idea of sending Ellie Arroway down a black hole. But he worried: Would the physics be right?

Sagan, who died two years ago, had a friend in Kip Thorne, the California Institute of Technology physicist who specializes in space and time warps.

Not only is a black hole a one-way street to oblivion, Thorne told Sagan, it would crush Arroway with a force of billions of tons per cubic inch.

So Thorne began to think about possible alternatives -- in particular, "wormholes," or tunnels through space and time, which few scientists had thought about very seriously. Thorne's work on wormholes not only gave Sagan a scientifically respectable way to get Ellie to Vega, it also opened up a new area of scientific research: the idea that the laws of physics might allow what Thorne calls "closed time-like curves" -- in other words, time machines.

What's a respectable physicist doing studying time travel? Thorne works on the boundary between science and speculation, on the cusp of what is and what might be. He's made a specialty of exploring the often outrageous consequences of Albert Einstein's theory of gravity: black holes, gravity waves, wormholes and various other bizarre objects that bend the mind almost as much as they distort space and time.

Still, Thorne doesn't see himself as "that far out on the edge." After all, time machines (possibly) and gravity waves (certainly) are consequences of Einstein's well-tested theory. In this context, even time machines aren't necessarily crazy ideas. "Ideas are crazy if they don't have any chance of being right," Thorne says.

In essence, he is crash-testing Einstein's laws of physics. The fundamental question that drives him is: What has Einstein's legacy left us? What kinds of objects should be produced by extremely warped space time, and how should they behave?

Back to the question Sagan first set Thorne to pondering 15 years ago: Could extremely warped space time create a wormhole that people could travel through, and if it could, would time travel be possible?

The answer is an issue of intense debate, at least for the few intrepid physicists willing to even consider the issue. These researchers are not interested in creating time machines so much as exploring the nature of space and time under extreme conditions.

Wormholes are theoretically plausible objects first discovered lurking in Einstein's equations in 1916. Unlike a black hole, a wormhole has two "mouths," an entrance and an exit -- essential requirements for any viable transport system. A wormhole mouth is a tear in the fabric of space time; it connects to the other tear, or mouth, which might be many light-years distant. Since the wormhole tunnels through four-dimensional hyperspace, it creates a shortcut through space and time.

As an analogy, imagine an ant walking from the left edge of this page to the right edge. The ant's flat, two-dimensional "space" (the page) is analogous to our everyday three-dimensional space, and the ant's route from the left to the right side of the page is analogous to a person's 26-light-year trip to the star Vega.

If you curl up the newspaper page so that the right edge touches the left edge, the ant could take a shortcut from one edge to the other. But the paper has to curve through three-dimensional space.

In the same way, a wormhole bores through four-dimensional space time to make a shortcut from Earth to Vega.

The problem -- amid the intense curvature of space time -- is keeping the wormhole open long enough to pass through. But after Sagan posed his question, Thorne put in some time "playing around with Einstein's equations" and discovered that a wormhole could be kept open. This would require filling it with exotic "negative" energy, which might not even exist.

The methods he used to arrive at this conclusion offer insights into Thorne's way of approaching problems far beyond the known.

First, he says, he makes some "guesses, based on knowledge and past experience," about what might happen to time in such a wormhole. He thinks about the problem in pictorial terms, "mostly shapes and curves," he says.

Thorne's thought experiments suggest that a wormhole could become a time machine.

The next step is to build a simple mathematical model -- or description -- and then to solve the equations. The math led him to the same conclusion: "The equations say unequivocally that [in the simplest case] if you had such a wormhole, it would convert itself into a time machine."

In fact, he said, it's "embarrassingly simple" to make a time machine with wormholes based on Einstein's laws of gravity.