Is time travel possible? - Colin Stuart
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0:07 - 0:08Have you ever daydreamed
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0:08 - 0:09about traveling through time,
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0:09 - 0:11perhaps fast forward in the centuries
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0:11 - 0:13and seen the distant future?
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0:13 - 0:15Well, time travel is possible,
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0:15 - 0:16and what's more,
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0:16 - 0:18it's already been done.
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0:18 - 0:19Meet Serge Krikalev,
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0:19 - 0:22the greatest time traveler in human history.
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0:22 - 0:24This Russian cosmonaut holds the record
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0:24 - 0:25for the most amount of time
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0:25 - 0:26he's been orbiting our planet,
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0:26 - 0:31a total of 803 days, 9 hours, and 39 minutes.
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0:31 - 0:32During his stay in space,
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0:32 - 0:34he time traveled into his own future
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0:34 - 0:38by 0.02 seconds.
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0:38 - 0:40Travelling at 17,500 miles an hour,
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0:40 - 0:42he experienced an effect
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0:42 - 0:43known as time dilation,
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0:43 - 0:45and one day the same effect
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0:45 - 0:47might make significant time travel
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0:47 - 0:49to the future commonplace.
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0:49 - 0:51To see why moving faster through space
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0:51 - 0:53affects passage of time,
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0:53 - 0:55we need to go back to the 1880s,
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0:55 - 0:56when two American scientists,
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0:56 - 0:58Albert Michelson and Edward Morley,
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0:58 - 1:00were trying to measure the effect
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1:00 - 1:01of the Earth's movement around the Sun
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1:01 - 1:03on the speed of light.
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1:03 - 1:04When a beam of light was moving
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1:04 - 1:06in the same direction as the Earth,
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1:06 - 1:08they expected the light to travel faster.
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1:08 - 1:11And when the Earth was moving in the opposite direction,
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1:11 - 1:13they expected it to go slower.
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1:13 - 1:15But they found something very curious.
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1:15 - 1:16The speed of light remained the same
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1:16 - 1:18no matter what the Earth was doing.
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1:18 - 1:21Two decades later, Albert Einstein was thinking
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1:21 - 1:22about the consequences
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1:22 - 1:24of that never-changing speed of light.
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1:24 - 1:25And it was his conclusions,
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1:25 - 1:28formulated in the Theory of Special Relativity,
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1:28 - 1:29that opened the door
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1:29 - 1:31into the world of time travel.
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1:31 - 1:33Imagine a man named Jack,
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1:33 - 1:34standing in the middle of a train carriage,
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1:34 - 1:36traveling at a steady speed.
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1:36 - 1:37Jack's bored
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1:37 - 1:39and starts bouncing a ball up and down.
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1:39 - 1:41What would Jill, standing on the platform,
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1:41 - 1:42see through the window
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1:42 - 1:44as the train rustles through.
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1:44 - 1:45Well, between Jack dropping the ball
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1:45 - 1:47and catching it again,
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1:47 - 1:48Jill would have seen him move
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1:48 - 1:50slightly further down the track,
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1:50 - 1:51resulting in her seeing the ball
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1:51 - 1:53follow a triangular path.
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1:53 - 1:55This means Jill sees the ball
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1:55 - 1:56travel further than Jack does
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1:56 - 1:58in the same time period.
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1:58 - 2:00And because speed is distance divided by time,
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2:00 - 2:03Jill actually sees the ball move faster.
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2:04 - 2:05But what if Jack's bouncing ball
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2:05 - 2:07is replaced with two mirrors
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2:07 - 2:09which bounce a beam of light between them?
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2:09 - 2:11Jack still sees the beam dropping down
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2:11 - 2:13and Jill still sees the light beam
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2:13 - 2:14travel a longer distance,
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2:14 - 2:16except this time Jack and Jill
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2:16 - 2:17cannot disagree on the speed
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2:17 - 2:18because the speed of light
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2:18 - 2:21remains the same no matter what.
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2:21 - 2:23And if the speed is the same
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2:23 - 2:24while the distance is different,
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2:24 - 2:28this means the time taken will be different as well.
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2:28 - 2:30Thus, time must tick at different rates
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2:30 - 2:32for people moving relative to each other.
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2:32 - 2:34Imagine that Jack and Jill have highly accurate watches
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2:34 - 2:38that they synchronize before Jack boards the train.
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2:38 - 2:40During the experiment, Jack and Jill would each see
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2:40 - 2:42their own watch ticking normally.
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2:43 - 2:45But if they meet up again later
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2:45 - 2:46to compare watches,
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2:46 - 2:48less time would have elapsed on Jack's watch,
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2:48 - 2:49balancing the fact
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2:49 - 2:52that Jill saw the light move further.
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2:52 - 2:54This idea may sound crazy,
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2:54 - 2:56but like any good scientific theory,
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2:56 - 2:58it can be tested.
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2:58 - 3:00In the 1970s, scientists boarded a plane
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3:00 - 3:03with some super-accurate atomic clocks
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3:03 - 3:03that were synchronized
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3:03 - 3:05with some others left on the ground.
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3:06 - 3:08After the plane had flown around the world,
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3:08 - 3:10the clocks on board showed a different time
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3:10 - 3:12from those left behind.
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3:12 - 3:14Of course, at the speed of trains and planes,
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3:14 - 3:16the effect is minuscule.
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3:16 - 3:17But the faster you go,
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3:17 - 3:19the more time dilates.
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3:19 - 3:21For astronauts orbiting the Earth for 800 days,
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3:21 - 3:23it starts to add up.
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3:23 - 3:26But what affects humans also affects machines.
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3:26 - 3:28Satellites of the global positioning system
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3:28 - 3:29are also hurdling around the Earth
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3:29 - 3:31at thousands of miles an hour.
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3:31 - 3:34So, time dilation kicks in here too.
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3:34 - 3:36In fact, their speed causes
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3:36 - 3:37the atomic clocks on board
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3:37 - 3:38to disagree with clocks on the ground
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3:38 - 3:41by seven millionths of a second daily.
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3:41 - 3:42Left uncorrected,
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3:42 - 3:44this would cause GPS to lose accuracy
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3:44 - 3:47by a few kilometers each day.
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3:48 - 3:50So what does all this have to do with time travel
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3:50 - 3:51to the far, distant future?
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3:51 - 3:53Well, the faster you go,
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3:53 - 3:55the greater the effect of time dilation.
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3:55 - 3:57If you could travel really close
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3:57 - 4:01to the speed of light, say 99.9999%,
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4:01 - 4:02on a round-trip through space
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4:02 - 4:05for what seemed to you like ten years,
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4:05 - 4:06you'd actually return to Earth
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4:06 - 4:08around the year 9000.
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4:08 - 4:11Who knows what you'd see when you returned?!?
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4:11 - 4:12Humanity merged with machines,
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4:12 - 4:14extinct due to climate change
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4:14 - 4:15or asteroid impact,
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4:15 - 4:18or inhabiting a permanent colony on Mars.
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4:19 - 4:19But the trouble is,
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4:19 - 4:21getting heavy things like people,
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4:21 - 4:22not to mention space ships,
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4:22 - 4:24up to such speeds requires
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4:24 - 4:27unimaginable amounts of energy.
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4:27 - 4:29It already takes enormous particle accelerators
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4:29 - 4:31at the Large Hadron Collider
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4:31 - 4:33to accelerate tiny subatomic particles
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4:33 - 4:35to close to light speed.
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4:35 - 4:37But one day, if we can develop the tools
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4:37 - 4:40to accelerate ourselves to similar speeds,
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4:40 - 4:41then we may regularly send time travelers
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4:41 - 4:42into the future,
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4:42 - 4:45bringing with them tales of a long, forgotten past.
- Title:
- Is time travel possible? - Colin Stuart
- Description:
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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.