Skip to main content

Time travel: Can it really be done?

By Paul Davies, Special for CNN
May 13, 2013 -- Updated 1612 GMT (0012 HKT)
The Sombrero Galaxy is thought to house a black hole, a gravitational field Davies says could lead to the future, but not the past.
The Sombrero Galaxy is thought to house a black hole, a gravitational field Davies says could lead to the future, but not the past.
STORY HIGHLIGHTS
  • Nearly 100 years ago, Albert Einstein showed that motion could stretch or shrink time
  • Fly from London to NYC and back and you leap forward a split second, Paul Davies says
  • He says a big time warp requires an intense gravitational field, such as a black hole
  • Going back in time would require a "wormhole," which he says is possible in principle

Editor's note: Paul Davies is author of "How to Build a Time Machine." He works at Arizona State University.

(CNN) -- Ever since H. G. Wells' trailblazing novel "The Time Machine," time travel has been a staple of science fiction. The idea of traveling through time is deeply fascinating: you get into a machine, press a few buttons, and step out not just somewhere else, but "somewhen" else. It's easy to imagine, but can it really be done?

Yes it can, at least in a limited sense. Over a century ago, Albert Einstein showed that time is intrinsically elastic, capable of being stretched or shrunk by motion. Fly from London to New York and back, and you will leap a split second into the future of stay-at-home Londoners. The effect can easily be measured using atomic clocks and involves only billionths of a second -- too brief for a person to notice, and hardly the stuff of "Doctor Who" television series-style adventures.

Paul Davies
Paul Davies

Read more: Scientists -- particles appear to travel faster than light

But time stretching can be magnified by increasing the speed. Close to the speed of light (about 300,000 kilometers per second), time warps become startling. Fly to the star Vega, 25 light years away, and back again at 99% of the speed of light, and when you return to Earth in 2062, you will have experienced only seven years travel time in the spacecraft. In effect, you will have leaped 42 years into Earth's future.

So travel into the future is not only possible, we have done it, although so far in only paltry amounts. How about going back in time? That is far more problematic and remains an active area of research. Einstein found that not only speed affects time, gravity does too. Time runs a little bit faster on the roof, where gravity is imperceptibly weaker, than in the basement, for example.

A really big time warp requires an intense gravitational field. Black holes are the best; near their surfaces time is slowed almost to a standstill relative to us. Indeed, black holes are black because outgoing light is trapped in slow motion. However, hanging out near a black hole is not only dangerous, it still only represents travel into the future; it gets you to the future quicker. Getting to the past requires something even weirder than a black hole -- a wormhole.

The mystery of black holes
Faster than the speed of light?
Black hole hunting satellite launched

Read more: The great time travel debate

Wormholes in space are shortcuts linking distant points -- a bit like that other sci-fi favorite, the star gate. Leap through one and you might come out on the other side of the galaxy a few minutes later. If wormholes exist, they could be adapted to make time machines that send you into the future if you traverse them in one direction, but into the past if you go in the other direction. Like a black hole, a wormhole would be a massive gravitational space and time warping object. But whereas a black hole represents a one-way journey to nowhere -- jump in and you can never get out -- a wormhole has an exit as well as an entrance.

Do wormholes exist? Black holes certainly do, but nobody has yet glimpsed any sign of its cousin, the wormhole. Furthermore, some physicists are so uneasy about their potential for being portals to the past that they flat-out reject the very idea. The problem concerns those familiar time travel paradoxes, like going back in time and murdering your mother before you were born. Physicists call these causal loop paradoxes, and they affront our desire for the universe to be a rational and ordered system. If cause and effect get muddled up in time, what does that do for our notions of reality?

Read more: 'Looper's' potential for real world time travel

In spite of these misgivings, there is nothing in Einstein's theory of space, time and gravitation to forbid journeying into the past, a possibility that Einstein himself hated. Not only wormholes, but several other mechanisms have been found that, according to Einstein's theory, can be used to travel back in time. All these proposals suffer from the problem of extreme impracticality, though. Building a human-sized wormhole, for example, would require harnessing vast amounts of peculiar quantum field energy and deploying gravitational stabilizing technology that would need the resources of a cosmic super-civilization.

For many scientists, however, it is the principle that counts, not the practical engineering. And here there is an intriguing possibility. Few physicists think Einstein had the last word on gravitation, and some modern extensions of his work make an extraordinary prediction. The Large Hadron Collider -- the giant accelerating machine that created the Higgs boson -- might just make a tiny wormhole for long enough that its time-bending effects could be glimpsed.

The opinions expressed in this commentary are soley those of Paul Davies.

ADVERTISEMENT
Part of complete coverage on
Space
September 20, 2014 -- Updated 1929 GMT (0329 HKT)
This image from the Hubble Space Telescope indicates that a huge ring of dark matter likely exists surrounding the center of CL0024+17 that has no normal matter counterpart.
Scientists are closer to seeing a vast, invisible universe as a spectrometer in Earth orbit picks up possible clues of dark matter.
September 10, 2014 -- Updated 1321 GMT (2121 HKT)
The Soviets sent stray dogs up to conquer space. This is what happened next
August 28, 2014 -- Updated 0920 GMT (1720 HKT)
Scientists believe that a hot gas bubble was formed by multiple supernovas.
August 27, 2014 -- Updated 1547 GMT (2347 HKT)
Robonaut is the next generation dexterous robot
Life aboard the International Space Station.
August 27, 2014 -- Updated 0153 GMT (0953 HKT)
NASA's New Horizons mission hurtles toward Pluto in historic 3 billion mile expedition.
August 6, 2014 -- Updated 2044 GMT (0444 HKT)
Rosetta spacecraft arrives at its destination, Comet 67P after a 10-year journey around the solar system.
After a 10-year chase the Rosetta spacecraft is now orbiting a comet
July 25, 2014 -- Updated 2016 GMT (0416 HKT)
"Here comes the sun" indeed, and it was just barely all right.
July 23, 2014 -- Updated 1653 GMT (0053 HKT)
Seems NASA's fascination with the moon is in the past. It's focused on something far more menacing: incoming asteroids
July 15, 2014 -- Updated 0356 GMT (1156 HKT)
Scientists looking for signs of life in the universe -- as well as another planet like our own -- are a lot closer to their goal than people realize.
August 25, 2014 -- Updated 1939 GMT (0339 HKT)
The U.S. Army brainchild "Project Horizon" was born. Its proposal to leap beyond the Soviets opened with the line: "There is a requirement for a manned military outpost on the moon."
August 25, 2014 -- Updated 1943 GMT (0343 HKT)
solar flare july 2014
From Earth, the sun appears as a constant circle of light, but when viewed in space a brilliant display of motion is revealed.
July 17, 2014 -- Updated 1731 GMT (0131 HKT)
The full moons of this summer -- July 12, August 10 and September 9 -- are supermoons, as NASA calls them.
June 29, 2014 -- Updated 1551 GMT (2351 HKT)
If you think you saw a flying saucer over Hawaii, you might not be crazy -- except what you saw didn't come from outer space, though that may be its ultimate destination.
June 27, 2014 -- Updated 0147 GMT (0947 HKT)
The U.S. space shuttle program retired in 2011, leaving American astronauts to hitchhike into orbit. But after three long years, NASA's successor is almost ready to make an entrance.
June 13, 2014 -- Updated 1421 GMT (2221 HKT)
When I first poked my head inside Virgin Galactic's newest spaceship, I felt a little like I was getting a front-row seat to space history.
June 10, 2014 -- Updated 2303 GMT (0703 HKT)
The sun is putting on a fireworks show again.
June 24, 2014 -- Updated 2302 GMT (0702 HKT)
A year is a very long time on Mars -- 687 days. NASA's Curiosity rover can attest that it's enough time for some unexpected life changes.
May 2, 2014 -- Updated 1800 GMT (0200 HKT)
At least one corner of the solar system may be serving up an ice-and-water sandwich, with the possibility of life on the rocks.
April 8, 2014 -- Updated 1555 GMT (2355 HKT)
You can't see it happening on Earth, but space itself is stretching. Ever since the Big Bang happened 13.8 billion years ago, the universe has been getting bigger.
February 25, 2014 -- Updated 2027 GMT (0427 HKT)
From a sheep ranch in Western Australia comes the oldest slice of Earth we know.
ADVERTISEMENT