F all the dreams of science fiction, time travel is the giddiest. To escape time is to escape everything — history, regret and, above all, death. Fed up with Victorian England? Speed to the distant future, as in H. G. Wells's 1895 classic, "The Time Machine." Miserable as an adult? Fly back to your own happier high-school days, as in two of this fall's new television shows. Angry at the end of life? Then choose cryonics, the most immediately available, if certainly the most inelegant, of time machines.

But is actual time travel possible? "The answer is a resounding maybe," said Paul C. W. Davies, a professor of natural philosophy at Macquarie University in Sydney. Dr. Davies is the author of "How to Build a Time Machine" (Penguin Putnam, 2002).

In the seemingly staid world of physics, time travel is all the rage. Some of the giants of physics like Kip S. Thorne of the California Institute of Technology, John A. Wheeler of Princeton University (who coined the term black hole) and the world's best-known physicist, Stephen W. Hawking of the University of Cambridge, have written books in the last few years with speculations about time travel.

"At first glance, it seems surprising that professional scientists are writing about such a wacky topic," Dr. Davies said. "But physics today is intimately involved with time, and studying time travel is a good way of testing and strengthening new theories."

But it isn't theory that excites the average person, it's the idea of a shiny new time machine gliding into the Jurassic Age or hovering over the battle of Waterloo. It's also the idea that time is dynamic and linear (like a videotape that can be rewound and fast-forwarded), while the positions of things in the universe (the earth, your high school), remain constant. Neither is the case, and even in concept, travel at will through time has inherent problems.

For those aiming backward in time, there's the "grandfather paradox," which raises the point that as a time traveler you could meet your grandfather, kill him, and thereby make your own existence logically impossible. The idea is that any physical movement into the past causes a change that sets up the paradox. The gentlest of time machines nudges the tiniest of butterflies, which unleashes a hurricane that kills your grandfather.

Pondering the paradox, Dr. Hawking concludes that nature may strive to protect chronology at all costs and, in his phrase, make the universe "safe for historians."

Then there is the view of time as videotape. If as a traveler you were to jump forward many years in time, you'd find that the Earth, the Sun — everything — had continued to move through space. Should you try to retrace your steps and return to your original time, you might return at the right date but the wrong place.

Perhaps most disappointing for science-fiction fans, Dr. Davies's time machine would not resemble a souped-up Delorean, like the one driven by Michael J. Fox in the "Back to the Future" movies. It would resemble, oddly enough, a mine shaft.

IF the universe is curved, as it seems to be, then crawling along its surface is the long way around. A much shorter route would be a mine shaft through the surface, much like a hole made by a worm as it burrows through an apple. Physicists call such a hole in space, which is similar to a black hole, a wormhole. If wormholes do exist, they would make quick paths through the universe — and through time.

The theory of relativity, after all, implies that space and time are one thing, called space-time. A wormhole through space is therefore a wormhole through time — voilà, a time machine. Of course, as with black holes, there is the problem of surviving the wormhole's immense gravitational field.

But for this and other problems, Dr. Davies can be encouragingly specific. For example, a heavy-ion accelerator like the one at the Brookhaven National Laboratory in Suffolk County is one necessary cog. But over all Dr. Davies's time machine is frustratingly intangible. Although it would require massive equipment like the ion accelerator, the "machine" would not be a vehicle at all but a vaporous pathway — a wormhole.

Of course, much of modern technology turns on the invisible. Power plants and their networks generate, amplify and transmit electrical energy, for instance. And cellular telephone networks find and amplify radio waves. Dr. Davies's proposed time machine would be a method for finding, amplifying and stabilizing wormholes, if they exist.

But if this machine is not quite what the average person would expect, neither are its abilities. If travel into the past is problematic, travel into the future would still be highly dangerous. For example, the wormhole's huge gravitational field could tear a traveler to shreds.

"It's still going to be a hairy ride," Dr. Davies said.