Reported by Science Journal editor Sharon Begley
of the Wall Street Journal
Wall Street Journal
Friday, November 21, 2003
by Sharon Begley
Physicists Are Looking At How We Might Take A Trip Through Time
Ronald Mallett hadnt even heard of physics when he read H.G. Wells 1895
classic, "The Time Machine," just a few months after his father died at age
The 10-year old assumed that to build such a device, and see his father again, he should
go into electronics, his dads field. It was only during his stint at the Strategic
Air Command that he learned that it was physicists who were discovering seeming
impossibilities: that space can bend, time can slow, particles can be waves and waves,
particles. It was physics, he realized, that offered the hope of making Wells
fiction - and his boyhood hope - a reality.
"But I was astute enough not to tell people I was interested in the physics of time
travel," says Dr. Mallett, a professor of physics at the University of
Connecticut, Storrs. "I chose black holes as my cover story, and didnt come out
of the time-travel closet until 1998."
The closet is emptying fast. Ever since Einstein formulated his general theory of
relativity in 1915, describing gravity as dips and curves in the single entity called
space-time, researchers have been finding hidden gems in its equations. Those equations
permit numerous "solutions," or particular shapes of space-time - from deep
wells to gentle waves. One solution, for instance, implies the existence of black holes;
at first only theorized, black holes have since become, through astronomical observations,
members in good standing of the cosmic menageries. Now physicists are taking seriously the
newest solutions, those that imply geometries of space-time that actually allow travel to
Prof. Mallet theorized in 2000 that if a powerful laser light were bent into a
ring, it would create a region at its center where space-time curves back on
itself so severely that someone proceeding into the future would wind up back when he
started, in his own past. In 1991, Princeton University astrophysicist J. Richard Gott
theorized that cosmic strings, thinner than an atomic nucleus but infinitely long and more
massive than a galaxy, could warp space-time enough to create these paths to the past,
called closed timelike curves.
But it is a 1989 discovery, by Caltechs Kip Thorne and colleagues, that has done the
most to get the physics of time travel into reputable scientific
journals. They theorized that general relativity permits wormholes - tunnels
that cut across a curved region of space-time, connecting here to there and
now to then. Earlier calculations suggested that wormholes dont stay open
long enough to serve as practical time machines, but Prof. Thorne showed that, with enough
negative energy, they can be propped open.
Thats how the heroes of "Timeline," in theaters next week, travel back to
the 14th century (and immediately plunge into nonstop sword-wielding,
horse-galloping mayhem). In the film, scientists accidentally discover a
wormhole, one end of which is anchored in 1357 France. That gets a thumbs up from
physicists: If wormholes and closed timelike curves exist, they are going to be found, not
created. Youd have to settle for whatever endpoints they have.
Just because wormholes emerge from general relativity doesnt mean they emerge in
reality, of course. But physicists take them seriously because of their experience with
black holes, which were first only theoretical, too. Maybe wormholes, too, will move from
theory to reality.
"In physics," says physicist Michio Kaku of the City College of New York,
"that which is not forbidden is mandatory. If you want to forbid some bizarre
phenomenon, you have to kill it by showing that a law of physics prevents it."
No one has yet done that with wormholes or time travel. The energy needed to prop open a
wormhole is about what you would get by converting the mass of a large star into energy
through E = mc2. But that is practical, not a fundamental, objection. British cosmologist
Stephen Hawking once proposed a "chronology protection conjecture" that would
forbid time travel as a result of the laws of physics, but has since retreated.
That has brought a sea change to physics. "A dozen years ago, if you talked about
time travel your name would be mud," says Prof. Kaku. "But now we feel that by
exploring the possibility of time travel, we are testing the extremes of the laws of
physics, which may lead to new physics."
If new physics is lurking anywhere, a good place to check is the sub-subatomic world of
"quantum foam." In this roiling microworld, space itself is holey, and wormholes
and black holes 100 billion billion times smaller than a proton constantly pop into
existence (as the blip that became our universe probably did) only to quickly disappear
(as our universe didnt). But it might be possible to pump enough energy into an
otherwise transitory wormhole it to keep it around.
Physicists even have the engineering specs for how to then turn a wormhole into a time
tunnel. Anchor one mouth in the present - say Nov. 21, 2010. Drag the other mouth through
space at nearly the speed of light, until Nov. 21, 2011. Moving objects age more slowly
than stationary ones, according to relativity. If you hop inside the wormhole, therefore,
you could travel to any point in time in-between, back to 2010.
And theres the rub. Time travelers could never reach a time
earlier than when a wormhole was engineered. No wonder none have visited us.