Is it possible to travel through time? Einstein’s theory of relativity states that the stronger the gravitational pull on an object, the more time slows for that object. Scientists predict that if someone were to travel to a place with a lot of gravity, like near a black hole, time would pass more slowly for that person. In this video excerpt from NOVA’s "The Fabric of the Cosmos: The Illusion of Time", host and theoretical physicist Brian Greene takes a journey through space—and time—to illustrate what time travel might really be like.
BRIAN GREENE Is it possible to travel to the future or the past?
AIRPLANE BOARDING ANNOUNCEMENT (Dramatization): Now departing for 50 years in the future, Flight 24.
BRIAN GREENE And if we could time-travel, would it be anything like what we all imagine?
(Film Clip): Catapult you through time to a world that has yet to be.
(Film Clip): The time travelers!
(Film Clip): Suppose something goes wrong with the time machine again?
(Film Clip): Throw the switch, Jed.
(Film Clip): Could we go anywhere we want, at any time?
(Film Clip): We're going to attempt time travel.
BRIAN GREENE No one outside Hollywood has made a working time machine just yet, but surprisingly, time travel might be possible.
AIRPLANE BOARDING ANNOUNCEMENT (Dramatization): Now boarding, Flight 24 to Black Hole Cygnus X-1.
BRIAN GREENE One way to travel through time is to make use of a strange feature of gravity. The familiar force that keeps our feet planted to the ground can have a profound impact on time.
See you later, sir.
BRIAN GREENE (Dramatization) Right, much later.
(Narration) So how can gravity be used to make a time machine?
Well, Einstein's theories show that gravity, like motion, can affect time. It's as if gravity can pull on time, slowing its passage. And the stronger the gravitational pull, the more time slows. Here on Earth, the effect is too small to notice, but still very real.
Compared to someone living on the top floor of a skyscraper, someone living on the bottom experiences time elapsing slightly slower because gravity is just a tiny bit stronger closer to the ground. But if you could travel to a black hole, the effect of gravity on time would be huge.
Formed when large stars collapse in on themselves, black holes have immense gravitational pull, millions and even billions of times stronger than the Earth's. And if someone watched you travel close to a black hole, they'd see time, for you, slow down dramatically.
JANNA LEVIN You, near that black hole, will appear to your friend far away to be moving slowly, talking slowly, biologically aging slowly. To them years are passing while for you it might be minutes.
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