Is time travel possible? - Colin Stuart
-
0:07 - 0:09Have you ever daydreamed
about traveling through time, -
0:09 - 0:13perhaps fast forward in the centuries
and seeing the distant future? -
0:13 - 0:15Well, time travel is possible,
-
0:15 - 0:18and what's more, it's already been done.
-
0:18 - 0:19Meet Sergei Krikalev,
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0:19 - 0:22the greatest time traveler
in human history. -
0:22 - 0:24This Russian cosmonaut holds the record
-
0:24 - 0:26for the most amount of time
spent orbiting our planet, -
0:26 - 0:30a total of 803 days,
9 hours, and 39 minutes. -
0:31 - 0:32During his stay in space,
-
0:32 - 0:34he time traveled into his own future
-
0:34 - 0:37by 0.02 seconds.
-
0:38 - 0:40Traveling at 17,500 miles an hour,
-
0:40 - 0:43he experienced an effect
known as time dilation, -
0:43 - 0:45and one day the same effect
-
0:45 - 0:48might make significant time travel
to the future commonplace. -
0:50 - 0:53To see why moving faster through space
affects passage of time, -
0:53 - 0:55we need to go back to the 1880s,
-
0:55 - 0:56when two American scientists,
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0:56 - 0:58Albert Michelson and Edward Morley,
-
0:58 - 1:02were trying to measure the effect
of the Earth's movement around the Sun -
1:02 - 1:03on the speed of light.
-
1:03 - 1:06When a beam of light was moving
in the same direction as the Earth, -
1:06 - 1:08they expected the light to travel faster.
-
1:08 - 1:11And when the Earth was moving
in the opposite direction, -
1:11 - 1:13they expected it to go slower.
-
1:13 - 1:15But they found something very curious.
-
1:15 - 1:18The speed of light remained the same
no matter what the Earth was doing. -
1:18 - 1:21Two decades later,
Albert Einstein was thinking -
1:21 - 1:24about the consequences
of that never-changing speed of light. -
1:24 - 1:25And it was his conclusions,
-
1:25 - 1:28formulated in the theory
of special relativity, -
1:28 - 1:31that opened the door
into the world of time travel. -
1:31 - 1:33Imagine a man named Jack,
-
1:33 - 1:35standing in the middle
of a train carriage, -
1:35 - 1:36traveling at a steady speed.
-
1:36 - 1:39Jack's bored and starts bouncing
a ball up and down. -
1:39 - 1:42What would Jill, standing on the platform,
see through the window -
1:42 - 1:44as the train whistles through?
-
1:44 - 1:47Well, between Jack dropping the ball
and catching it again, -
1:47 - 1:50Jill would have seen him move
slightly further down the track, -
1:50 - 1:52resulting in her seeing the ball
follow a triangular path. -
1:53 - 1:56This means Jill sees the ball
travel further than Jack does -
1:56 - 1:58in the same time period.
-
1:58 - 2:00And because speed
is distance divided by time, -
2:00 - 2:03Jill actually sees the ball move faster.
-
2:04 - 2:07But what if Jack's bouncing ball
is replaced with two mirrors -
2:07 - 2:09which bounce a beam of light between them?
-
2:09 - 2:11Jack still sees the beam dropping down
-
2:11 - 2:14and Jill still sees the light beam
travel a longer distance, -
2:14 - 2:17except this time Jack and Jill
cannot disagree on the speed -
2:17 - 2:21because the speed of light
remains the same no matter what. -
2:22 - 2:24And if the speed is the same
while the distance is different, -
2:24 - 2:27this means the time taken
will be different as well. -
2:28 - 2:32Thus, time must tick at different rates
for people moving relative to each other. -
2:32 - 2:35Imagine that Jack and Jill
have highly accurate watches -
2:35 - 2:38that they synchronize
before Jack boards the train. -
2:38 - 2:40During the experiment,
Jack and Jill would each see -
2:40 - 2:42their own watch ticking normally.
-
2:43 - 2:46But if they meet up again later
to compare watches, -
2:46 - 2:48less time would have
elapsed on Jack's watch, -
2:48 - 2:52balancing the fact that Jill saw
the light move further. -
2:52 - 2:54This idea may sound crazy,
-
2:54 - 2:56but like any good scientific theory,
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2:56 - 2:57it can be tested.
-
2:58 - 3:00In the 1970s, scientists boarded a plane
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3:00 - 3:03with some super-accurate atomic clocks
-
3:03 - 3:05that were synchronized
with some others left on the ground. -
3:06 - 3:08After the plane had
flown around the world, -
3:08 - 3:10the clocks on board
showed a different time -
3:10 - 3:12from those left behind.
-
3:13 - 3:15Of course, at the speed
of trains and planes, -
3:15 - 3:16the effect is minuscule.
-
3:16 - 3:19But the faster you go,
the more time dilates. -
3:19 - 3:21For astronauts orbiting
the Earth for 800 days, -
3:21 - 3:23it starts to add up.
-
3:23 - 3:26But what affects humans
also affects machines. -
3:26 - 3:28Satellites of the global
positioning system -
3:28 - 3:29are also hurdling around the Earth
-
3:29 - 3:31at thousands of miles an hour.
-
3:31 - 3:33So, time dilation kicks in here, too.
-
3:34 - 3:37In fact, their speed causes
the atomic clocks on board -
3:37 - 3:39to disagree with clocks on the ground
-
3:39 - 3:41by seven millionths of a second daily.
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3:41 - 3:42Left uncorrected,
-
3:42 - 3:44this would cause GPS to lose accuracy
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3:44 - 3:46by a few kilometers each day.
-
3:48 - 3:50So, what does all this have
to do with time travel -
3:50 - 3:52to the far, distant future?
-
3:52 - 3:55Well, the faster you go,
the greater the effect of time dilation. -
3:55 - 3:57If you could travel really close
-
3:57 - 4:01to the speed of light, say 99.9999%,
-
4:01 - 4:02on a round-trip through space
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4:02 - 4:05for what seemed to you like ten years,
-
4:05 - 4:06you'd actually return to Earth
-
4:06 - 4:08around the year 9000.
-
4:08 - 4:11Who knows what you'd see
when you returned?! -
4:11 - 4:12Humanity merged with machines,
-
4:12 - 4:15extinct due to climate change
or asteroid impact, -
4:15 - 4:18or inhabiting a permanent colony on Mars.
-
4:19 - 4:20But the trouble is,
-
4:20 - 4:23getting heavy things like people,
not to mention space ships, -
4:23 - 4:27up to such speeds requires
unimaginable amounts of energy. -
4:27 - 4:29It already takes enormous
particle accelerators -
4:29 - 4:31like the Large Hadron Collider
-
4:31 - 4:35to accelerate tiny subatomic particles
to close to light speed. -
4:35 - 4:39But one day, if we can develop the tools
to accelerate ourselves to similar speeds, -
4:40 - 4:41then we may regularly send time travelers
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4:41 - 4:43into the future,
-
4:43 - 4:45bringing with them tales
of a long, forgotten past.
- Title:
- Is time travel possible? - Colin Stuart
- Description:
-
View full lesson: http://ed.ted.com/lessons/time-travel-and-einstein-s-special-relativity-colin-stuart
Time travel is a staple of science fiction stories, but is it actually possible? It turns out nature does allow a way of bending time, an exciting possibility suggested by Albert Einstein when he discovered special relativity over one hundred years ago. Colin Stuart imagines where (or, when) this fascinating phenomenon, time dilation, may one day take us.
Lesson by Colin Stuart, animation by TED-Ed.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:04
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TED edited English subtitles for Is time travel possible? - Colin Stuart | ||
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Krystian Aparta
The English transcript was updated on 2/13/2015.