Did you know that astronauts on the
International Space Station age
more slowly than us here on Earth?
But does that mean that all
space travel makes you young?
I'm going to take a two minute
elevator ride to find out.
Hey Devika.
Hello Rad.
So I hear you're going to teach me
about time and space.
I'm gonna try.
This is a great time to do it and a
great space to do it.
So are you ready?
Absolutely.
Let's do this.
Going up to level 45 and back
down. Okay, so I have
heard that time moves
differently if you're in space.
What is that about?
Let's imagine I'm sending you on a
spaceship.
Yay!
And you are zipping through space
near the speed of light.
When I'm measuring your time, time
is going to go slower for you.
Time is going to be going slower
compared to the surface of Earth.
So it's all about that relative.
Yes.
And high speeds.
Yes. Okay.
Right. So it depends on how
far you go and how fast you
go.
How?
So for example, let's imagine you
are on that spaceship and you are
doing a little experiment.
You have a detector that is sending
out a light pulse, which is going up
to a mirror.
It's bouncing off the mirror and
coming back into the detector.
So this whole thing is taking
one second.
Now, of course, light has a constant
speed, so this speed
cannot change.
Think of it as the clock.
One second, one second, one second,
one second. Now I'm looking at it
standing on an asteroid.
And when I look at the
light pulse, I also have to take
into account the forward
motion of the spaceship.
The time it takes, from my
perspective, for the pulse
to go from the detector,
reach the top and then come back
is not going to be a straight line,
but it's actually going to do
something like this...
So I perceive relative
to me that the
time takes longer and that's time
dilation. Time is going to go slower
for you.
Because it's relative.
Yes, that's right.
Halfway through.
Time has to change to keep the
velocity of light a constant.
But if the time's just moving
relatively, it's not actually
like biologically or
in absolute terms different?
Not for you.
So for you, you wouldn't even notice
a thing. Your one second is going to
remain one second.
But biologically, say, twins, then
when the astronaut who goes to space
comes back, he would actually be
younger relative to his twin.
"Relative" to his twin, he'd
actually be younger.
The guy coming back.
Biologically speaking?
Biologically speaking. So the passage
of time would have gone slower
for him in space when he comes back.
I thought I understood it, but now
I think I have more questions
than when started.
Well that's a good place to be in.
But we're out of time.
I'm going to make it go slower next
time.
Thank you. Ahh!
So time dilation is affected
by extreme gravity and extreme
velocity.
And what this means is that time
is actually relative.
So while I can experience
here on Earth, a second as a second,
and an astronaut in space could
experience a second as a second,
when we compare that,
when we look at my time compared
to all the passing of their time,
it's actually different.
And that's because of the gravity
and velocity that they're
experiencing, which is different to
what I'm experiencing.
So while I might think that time
is absolute and it is experienced
the same everywhere in the universe,
it kind of is but
then kind of isn't because it's
the relativity, it's the comparison,
which is where you see that it's
different.
It's very complex, it's very
upsetting.
Hey, thanks for watching.
If you're like me and you want to
learn more about special relativity,
then please give this video a big
thumbs up so I can convince them to
let me do this again and learn more.
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