- 2 years ago
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Life Posters, only available on the kurzgesagt shop here:
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Time travel is possible. In fact, you've been doing it since
the day you were born. But what if we told you there's a
way to hack the universe and manipulate time itself?
We just have to do two simple things to make it happen:
1. Make a lot of physicists grumpy.
2. Shoot one twin through space against their will, while
the other chills on Earth.
Let's go!
these topics and more with a free 30-day trial + 20% off
the premium subscription! This video was sponsored by
Brilliant.
Thanks a lot for the support!
Go on your very own time travel adventure with our
Timeline of Human History and Timeline of Complex
Life Posters, only available on the kurzgesagt shop here:
https://shop.kgs.link/TimeTravel
Sources & further reading:
https://sites.google.com/view/sources...
Time travel is possible. In fact, you've been doing it since
the day you were born. But what if we told you there's a
way to hack the universe and manipulate time itself?
We just have to do two simple things to make it happen:
1. Make a lot of physicists grumpy.
2. Shoot one twin through space against their will, while
the other chills on Earth.
Let's go!
Category
📚
LearningTranscript
00:00You're going forward through time, one second at every second.
00:04Congratulations!
00:05You're a time-traveller!
00:06A bit lame, but let's start here to get to the fun of real time travel, to ride on dinosaurs
00:13and high-five Einstein.
00:15Time isn't really a thing that passes, but a dimension, a direction you can move in.
00:20We think our universe is four-dimensional, with three spatial and one time dimensions
00:25smooshed together into a fancy thing we call space-time.
00:29What you experience as time passing and your life happening is actually you moving through
00:34the time dimension.
00:36And this dimension is a bummer.
00:38While you can go forward-backward, left-and-right, up-and-down in the space dimensions, in time
00:44you can only go forward.
00:47You only get older, never younger.
00:49You can't make detours.
00:51But this is an illusion.
00:53You have far more control over how you move through time.
00:56To explain how this actually works, without making a maths video, we have to make a lot
01:01of physicists grumpy, so please keep in mind that we're simplifying and lying a bit.
01:06Okay, so there's a very strange rule.
01:09Everything in our universe moves at the speed of light through four-dimensional space-time.
01:14Your speed through space-time is the sum of your separate speeds through time and space.
01:20It's impossible for you to stay still.
01:22Even if you're not moving through space dimensions, you're moving through the time dimension,
01:26blasting face-first into the future.
01:29You can slow down in the time dimension by moving faster through the space dimensions,
01:33but in total, you will always move at the speed of light through space-time.
01:38If you could somehow truly stand still in space, you'd still move through time at the
01:42speed of light.
01:43And the other way round.
01:45Photons, light particles, move at the speed of light through space.
01:49They don't experience any time passing, because their speed in that time dimension is zero.
01:55In the time dimension, they're frozen in place.
01:58If you see light on Earth, from the photon's perspective, it was just on the surface of
02:02the sun, and then suddenly crashed into your eye, with nothing happening in between.
02:07Remember, we're telling a science story here.
02:13In real life, things are more complicated.
02:15For one, it's impossible to truly stand still relative to space itself.
02:19You can only be standing still relative to other things in space.
02:23And you can't really define a reference frame for photons as we just did.
02:27For details, check out our sources.
02:29But now, back to our story.
02:31Okay, so everything in the universe moves at the same breathtaking speed, but this speed
02:36is split between space and time.
02:40Which leads to all sorts of wacky things, and where we can see time travel happen.
02:46Real and easy time travel.
02:48When a bus drives past you, it's moving a little bit faster through space than you are.
02:53So it moves slower through time than you.
02:55Or how it's usually worded, the bus is moving slower through time relative to you.
03:01While this makes things feel like weird physics magic, it's very simple.
03:05Move faster through space, go slower in time.
03:08Move slower through space, go faster in time.
03:12And if you had another person moving way faster or slower than you, both end up travelling
03:16different distances in the time dimension.
03:19The story that's usually told to demonstrate this is to get twins, force one of them into
03:23a rocket against their will, shoot them through space super fast while the other twin chills
03:28on earth.
03:29And because one twin moves very fast through space, while the other moves slowly on earth,
03:33they move at different speeds through time.
03:36When the rocket finally gets home, they're no longer the same age, and the younger space
03:40twin is ready to start years of therapy for being abducted by theoretical physicists.
03:44This is the twin paradox, and it makes perfect sense within the rules of the universe.
03:49If you want to learn more about the paradoxes of time, we made a video about it.
03:53But in a nutshell, you're using time dilation, the fact that your position in time is subjective
03:58and only true for yourself.
04:01With sufficiently fast rockets, you could get as far as you want into the future.
04:05Technically, this way you could witness the end of the universe, or look at the final
04:08thing that will ever happen.
04:10We also made videos about that.
04:13We should mention that there's another way to jump forward in time.
04:17Active objects bend to space-time, causing time to go slower near them.
04:21On earth, the effect is tiny.
04:23The gravity of our planet makes time pass 0.00000007% slower than in deep space, far
04:32from any gravitational fields.
04:34Hardly useful for time travel, but it's a start.
04:37If you move into a really strong gravitational field, like around a black hole, the closer
04:42you get to the event horizon, the slower time passes for you.
04:46If we kidnap our twin again, they won't notice it at all.
04:48Their watch ticks as fast as it always does.
04:51But from the outside, they seem to almost stand still.
04:55Only when the twin leaves the gravitational field and comes back to earth, do they realize
04:58they time-traveled.
04:59Okay, so you can time-travel to the future by going fast or near a black hole.
05:05This is pretty lame and has literally only downsides except for people who want to sort
05:10of teleport into the future.
05:12And it makes building a gigantic human space empire super hard, because even if we develop
05:16the technology to go really super fast between stars, going on a faraway journey will always
05:21mean leaving your home as you knew it forever.
05:24But now that we know all of this, there's actually a way we could use the rules of our
05:28universe to travel backwards through time.
05:31The past is a faraway land.
05:34Let's go there.
05:35So you always move through space-time at the speed of light.
05:39If you go fast through the space-dimension, you slow down in the time-dimension.
05:43And here we find an actual opening for backwards time-travel.
05:47The theory of relativity, which may be the most solid scientific theory we know, does
05:51not forbid faster-than-light motion through space.
05:55If you move through the space-dimension faster than the speed of light, superluminal, you
05:59need to move through the time-dimension with negative speed.
06:02That means you go backwards through time relative to the rest of the universe, into the past.
06:08Many scientists have been looking for superluminal particles and given them a name, tachyons.
06:14They could exist and would have wild properties like getting faster when they lose energy
06:18and of course travelling backwards in time.
06:21Finally, real time travel.
06:24Just like with photons, it isn't really possible to clearly define how time passes for tachyons
06:29themselves.
06:30It depends on how you move through space-time relative to them.
06:33But now, for the first time, some observers could actually see tachyons literally travelling
06:37backwards in time, which means they could be used to directly interact with the past.
06:43In theory, you could use them to send messages to your past self and change all sorts of
06:47things that have already happened.
06:50Maybe with some tachyon-powered sci-fi future tech, you could see a star die before it was
06:54born, meet your great-grandparents, prevent your past self from making that one dumb mistake,
07:00win the lottery or get eaten by dinosaurs, and create juicy time paradoxes that also
07:06kind of break the universe.
07:08Oh, what's that?
07:11Right.
07:12Hmm.
07:13It seems there are things in our universe that are impossible to mix.
07:18Unfortunately, the theory of relativity specifically forbids anything that starts out travelling
07:23slower than the speed of light to reach the speed of light, because moving faster through
07:28space requires energy, and the energy required to reach the speed of light is literally infinite.
07:34Even if you could gather all the energy of the universe, you couldn't accelerate a grain
07:38of sand to the speed of light.
07:40You can get as close as you like, but you can never reach it.
07:43It is possible to move at the speed of light as photons do, but they always move at the
07:48speed of light.
07:49If you move superluminally, you will always move superluminally.
07:54And sadly, so far, we don't have the tiniest bit of evidence that tachyons exist.
07:59While they work on paper, most scientists think they're not real.
08:02So for now, it seems that time travel into the past is strictly impossible, no matter
08:07how hard we try.
08:09The past is a faraway land, and while we can look at it in pictures and movies and our
08:13memories, it's locked away, forever outside of our reach.
08:18While this is sad, it leaves you with the most important time there is, right now, the
08:23moment where you actually exist, and a future that's yours to forge.
08:28If you want, you could even time travel to it.
08:33Luckily, shaping the future is much easier than trying to change the past.
08:40With the right knowledge and problem-solving skills, you'll be ready for whatever obstacles
08:44or opportunities lie ahead, which is where our friends at Brilliant come in.
08:49Brilliant will make you a better thinker and problem-solver, with thousands of interactive,
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10:05ends.
10:06We've found a way to evade the laws of the universe and go on a truly breathtaking time
10:11travel adventure.
10:12Are you ready?
10:13Well, too bad.
10:16Here we go!
10:18Look, it's the human era.
10:2212,000 years of human innovation brought to life.
10:26Absolutely incredible how our ancestors laid the foundation for the life we lead today.
10:30Let's go back even further and take a look at the timeline of life.
10:34Wow, humans are only a tiny blip at this scale.
10:38Mammals haven't been around for long either.
10:40Here's the age of the dinosaurs.
10:43And going further back, we can see where it all began.
10:47You can now go on your very own time travel adventure with our timeline of human history
10:51and timeline of complex life posters.
10:54They're expert approved and designed with great love and care.
10:58Get them both to get the full time travel effect and to support everything we do on
11:02this channel.
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