Time Travel Isn't What It Used to Be

[Guest guest]

Time Travel Isn't What It Used to Be

By ANTHONY RAMIREZ

from NYtimes

 

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.