September 10, 2001

magine for a moment that you have access to a time machine. You realize you could travel back in time, see your grandparents as young adults, and learn about their lives.

You hop into the machine. But when you find your grandfather, he's not happy that a wild-eyed stranger has inexplicably shown up, making outrageous claims about coming back from the future. He's so upset that he completely forgets the fact that he has a date that evening. The young woman he stands up happens to be your grandmother, and - thanks to your untimely intervention - they never meet. Thus, of course, your father or mother is never born.

So here's the question: How come you're still here to go back in time and pester the old man? The simplest answer, explains Professor Ronald Mallett, is that you can't go somewhere else in time and make changes that will affect your present. The dynamics predicted by quantum theory won't let you.

The story is called the "Grandparent Paradox" and it's no parlor game. Among scientists who ponder the possibility of time travel, it's a classic conundrum. According to quantum theory, practically an infinite number of possibilities exist simultaneously. If you traveled through time, you could encounter yourself in any of the alternative scenarios, but you could not alter the flow of your own space-time continuum. It's physically impossible.

Mallett knows about these things, because he's a physicist. He also firmly believes time travel is possible. Sometime next year, in fact, he hopes to produce the first piece of technology that eventually will allow him to build a time machine. It will be a device that employs lasers to actually twist space. And he plans to build it right here, at the University of Connecticut.

Forty-Six Years of Time Travel
Mallett's quest to build a time machine began nearly half a century ago, with the collision of two dramatic events. He was 10 years old and had just finished reading H.G. Wells' novel, The Time Machine, when his father died suddenly of a heart attack.

For the young boy, the notion of building a time machine and going back to save his father's life became a fantasy that helped him through his grief. In time, it also fueled his adult imagination, as he earned his B.S., M.S., and Ph.D. degrees in physics at Penn State and, in 1975, embarked upon a distinguished career at UConn. His field of specialization has been theoretical general relativity and relativistic quantum mechanics.

A special area of interest has been black holes, those pockets in space where dying stars have collapsed upon themselves with such unimaginable force that nothing - not even light - can escape from their gravity. Mallett's interest in black holes furthered his understanding of the connection between gravity and curvature of space-time. Since gravity, according to Einstein's general theory of relativity, amounts to the curvature of time and space, it follows that a really strong gravitational field, like that of a black hole, could actually bend light and slow - or possibly even stop - time.

The Door to Yesterday
In 1998, at a physics conference in Kentucky, Mallett met University of Michigan astrophysicist Fred Adams and discovered they shared an interest in time travel. Fascinated by Mallett's research, Adams encouraged him to write a book on time travel for the popular market.

"When I began researching the book, I discovered there was a ton of literature in the scientific journals," Mallett recalls. It was a profoundly liberating moment. For years, fearing skepticism, he had concealed his research from his colleagues. Now he realized there was extensive professional interest in the topic.

The professional literature showed that closed loops in time (physicists' jargon for time travel into the past) were possible for such exotic objects as rotating black holes, wormholes, and cosmic strings.

In Einstein's theory both matter and energy can bend space and time. Light does not have mass but it does have energy. This led Mallett to consider the possibility of using a circulating beam of light to twist space and create closed loops in time. He was convinced that in the gravitational field caused by a circulating laser beam, particles of matter could be moved through vortices in space and time in a laboratory. And if that could be done, then perhaps with sufficient energy larger objects, such as people, could be moved as well.

When an article about his time machine concept appeared last spring in the magazine New Scientist, he became quite a celebrity. Throughout the summer he was interviewed by print and broadcast journalists from all over the United States and abroad.

The publicity "has gotten a lot of people interested," he says, "not just in me and my work, but also in UConn. A lot of exciting work is being done here in our physics department, and I get e-mails now from many students interested in coming to UConn.

"I'm also gratified by the response I've had from other scientists," he adds. "Many are still skeptical, but there is real interest in my work and its implications for other lines of research. The head of our department, Professor William Stwalley, for instance, doubts time travel can actually happen, but he's very supportive of my research."

Interestingly, one of the things provoked by the publicity has been a dialogue about the ethics of time travel. And that, in turn, leads to the Grandparent Paradox. Mallett's quest to produce a time machine began with his desire to go back in time and save his father's life. Now he realizes he can never do that. Even if he's successful, time travel will only be possible from the moment the machine is turned on. Leaving the time machine turned on would allow future time travelers to visit our present moment, their past. But they would be barred from visiting earlier times.

Still, sometime within the next few years, Mallett hopes his theory will get a critical test. Perhaps he and a colleague will light up a laser device designed to twist space. If it works, then he feels confident the resources to advance the concept will quickly follow.

After that, time travel may be, well, just a matter of time.

Jim Smith