All language subtitles for genius.by.stephen.hawking.part6.where.are.we.480p.hdtv.x264.rmteam_track3_eng

We all have questions.

Big questions.

How big is the universe?

It's part of
what it means to be a human.

Man, voice-over: How far
away are the stars?

Joy to boat.

My name is Stephen Hawking

and I believe that
anyone can answer

big questions for themselves.

This is exciting.

So, with the help
of a few ordinary people...

And a team of experts...

Where you are changes
how we see the universe.

We are going
on the ultimate voyage.

These distances are just
getting bigger and bigger.

A quest to answer the greatest

mysteries of the universe.

Right, let's blow
this bad boy up.

Using the power
of the human mind.

We made it!

Because anyone
can think like a genius.

Where are we?

Where are we?

That's a pretty
profound question.

If we didn't know where we are,

we'd be like
monkeys in a forest,

totally unaware of our position
in the cosmos.

Fortunately, we humans
know everything,

from the shape of the Earth
to its place in the universe.

But how did we find out?

I believe anyone
can work it out.

Let's see if I'm right.

I have asked 3 ordinary people

to come on a journey
of discovery.

They will have
tools and equipment,

and I want to see
if they can grasp

the true scale of
the universe...

With some fun experiments
to find out where we are.

Where are we?

That's a really good question.

We're on Earth.

Yet, there's more
planets out there.

In my solar system.

And the Milky Way.

That's where I'm at.

But how do we know for sure?

The first step is
to measure our planet.

How big is it
and is it really round?

The volunteers don't know it,
but they are going to find out

the size and shape of the world,
right here in Nevada.

They'll do it by tackling
their first challenge:

How flat is this lake?

How do you measure
the flatness of a lake?

With a huge ruler.

Yeah, she has a point, though.
You need...

You need something
that you know is flat

to measure the surface
of the water against.

Yeah.

This lake holds the secret

to the size and shape
of the Earth,

but can the team work it out?

To help them,
they need a few tools.

2 feet, 7 inches.

First is a powerful laser

which projects
a straight beam of light

across the surface of the lake.

Next, they'll need a boat.

Ah... Whoa, we just
passed through it.

Yeah.

Joy to boat.

This is cat, over.

I want you to go at
the front of the laser.

Roger.

Now we gotta turn
a little to the right.

If the lake is flat,
the laser beam and the water

will always be parallel
to each other.

Seen from a boat,
the beam would always stay

at the same height
above the water,

no matter how far you travel
into the lake.

But does that happen?

And can the team work out why?

Time to find out.

The boat has a whiteboard
attached to it,

which will be a target.

We're looking
for the laser beam,

so that we can mark it
on the whiteboard.

Oh, it's hitting off that.

And we made
the first measurement

and I was pretty confident that
we weren't gonna find anything.

A little more to the right.

Almost there.
There we go.

They take their first
reading 500 feet from the shore.

Ok, what was the height of it?

Got it.

For the next measurement,

they'll need to go
much further out.

Ok, so, now, I need you go out

3 miles away from the laser.

All right.

Awesome.

So, 3 miles away,
where's the laser beam?

Remember, if the lake is flat,

it would be
the same height as before.

Cat, you have to go
slightly to the left.

You say go slightly to the left?

Yeah.

A little bit more to the right.

Here we go.

I don't even think this beam

is gonna hit our boat.

So, we're gonna have to
measure it on something else.

- All right.
- I've no idea.

Here we go.
Oh, is that your...

Is that your measuring tool?

- Do you see it?
- Yup.

Can you mark it?

We made the second measurement

and my whole world fell apart.

It's like 6 feet.

Yeah.
Yeah.

It seems a lot higher.
Ok.

- You got it?
- Uh-huh.

All right.

Just 3 miles away,

the laser seems to have
risen by 6 feet.

But we know the beam is level,

so, that suggests that the lake
is now 6 feet lower.

To see a 6-foot drop,

when everything
looked flat to me,

was... was kind of mind-boggling.

Definitely kind of shattered my
perspective in about one second.

It made me rethink
what was going on.

Perception is still
it's a flat lake, but...

It's not a flat lake.

It's not a flat lake.

That was crazy.

I was definitely blown away
by the fact that

the laser was that
high off the water.

Hey.

Hey, joy.

- What's up?
- We're back.

So, how was it?

The laser was
6 feet up in the air

and we had to use this
board to mark it.

The lake is clearly not flat.

It's almost as if
it's sloping downhill.

With this realization,
my volunteers have made

their first step towards
measuring the entire world.

I think we should make some more
measurements, for sure.

Yeah, agreed.

Yeah, totally.

But they are
not the first people

to do it, of course.

In fact, the first person
to measure the Earth accurately

was an ancient Greek genius
named Eratosthenes.

More than
2,000 years ago, Eratosthenes,

a very clever philosopher,

mathematician, geometer,
from Greece,

he embarked on an experiment

to measure the diameter
of the Earth.

If the Earth was flat,

anywhere on the flat Earth at
a given time during the day,

we would see the Sun shining
with the same angle.

While, if it is round,
that won't be the case.

Eratosthenes had heard
that at noon

on the longest day of the year,

the Sun shines directly
down the water well

in what is now the city
of Aswan in Egypt.

Here, the Sun must be
directly overhead.

So, in another location,
500 miles to the north,

he made a second observation,

again at noon on
the longest day of the year.

Here, 500 miles north,
he performed this experiment

and he planted a pole vertical

and realized that the pole
was casting a shadow.

The shadow was
evidence that the Sun

is not overhead,
but at an angle.

By measuring this angle,

and knowing the distance
between the two locations,

he was able to calculate
that the Earth is a ball,

about 8,000 miles in diameter.

But the question is,
with the right tools,

can the volunteers match
this ancient genius?

Today, we use lasers and
GPS and all kinds of technology

to come more or less
to the same number.

This is what science is about.

It's about inventing new ways
of investigating nature,

looking for facts,
looking for measurements,

and coming with results
which are astonishing.

My volunteers have
discovered the lake is not flat,

but in order to measure
the whole world,

they need to make a new
measurement, much further away.

And to do that,
they will need some new tools.

Ok, let's get this box open.

All right.
Yeah.

Hey, what do we have here?

Tripod.
That's like a tripod.

Now instead of the laser,

a telescope will
enable our volunteers

to look in a straight line
to the lake's opposite shore.

But that's not the only
instrument they'll need.

We're wondering, ok, how
are we gonna get this next point

if it's so high,
it's past our board.

Whoa!

Very cool.

Are we getting in a helicopter?

This chopper appears
out of nowhere.

All right, that is awesome.

Just as the telescope
replaces the laser,

the helicopter takes
the place of the boat.

I'll stay with the telescope.

Ok, great.

We'll go in the helicopter.

- That's a plan.
- Sounds like a plan.

Yeah. All right, let's do it.

All right, we'll
go ahead and lift off.

This is exciting.

I love that there are no doors.

We're flying to pyramid rock.
Do you copy that?

I copy that. You are
flying to the pyramid.

The lake looks
completely flat from up here.

If they are twice as
far away as before,

how much lower will the far
shore of the lake appear to be?

Jim, we're going to be at
the top of the pyramid rock.

Oh, got 'em.

Yeah, I have you
on the telescope.

Go ahead and land.

As it lands,
it completely disappears

from my line of sight.

Joy, are you still airborne?

Yeah. Can you
see us landing?

The reports from the helicopter,

they're still flying,
but I can't see it.

To wrap your head around it
in that short of time

was a little difficult for me.

I was like, this is crazy.

We have landed in our position.

Ok, joy, go ahead and lift off.

They plan to ascend

until Jim can see them
on the horizon.

Then they'll tell him
their altitude.

Let me know when you can see us

on spot on the horizon.

Oh, I got 'em, I got 'em.

Ok, what's your
elevation right now?

All right, Brian, how many
feet are we above the lake?

24 feet.

Whoo!
We made it!

24 feet.

24 feet, awesome.

24 feet is a lot higher

than our other two points
that we got.

That was awesome.
It was great.

At 6 miles, the lake has fallen

4 times lower than before.

So, what is going on?

Ok, you guys, check this out.

So, if this line
is our laser beam.

Right.

That we shot across the lake.

Right? And that's the shore.

This is the laser.
Right there.

And we join our data points,

at 6 feet and then
all the way out to 24,

this is our source, that's
our flat line, right?

And this is the surface
of the lake.

The green line
shows the path of the laser

and the view from the telescope.

And the gold line shows
how the data points

form the beginning of a curve.

So, that means,
this lake isn't flat.

It's not even close.

No.

That's crazy.

If we can just
continue that curvature

all the way around
and complete a circle,

and we can measure it,

then that gives us

the circumference of the Earth.

With these
measurements on the lake,

we can calculate that
the Earth's circumference

is around 25,000 miles,

which matches
Eratosthenes's calculation.

I still have a hard time
wrapping my head around the fact

that we measured the Earth
at that lake.

I'll never look at
a lake the same way,

I'll never look at a big body
of water the same way,

now that I know it's following
the curvature of the Earth.

Knowing
the shape and size of the Earth

is just the beginning of
finding out where we are.

To learn more, we need
to journey into space,

to the Moon and beyond.

The Moon is our
nearest neighbor,

but very few people realize
its distance from Earth.

So, the next challenge
in finding out where we are

is to find out how far away
the Moon really is.

To discover this,
we need to leave the lake

and head deep into
the vast Nevada desert.

So, what's in the box?

Ok.

So, it's a tiny Earth
and a tiny moon.

These are scale models
of the Earth and the Moon.

Their relative size
was first discovered

by the ancient greeks,
thousands of years ago.

Back then, the genius
who worked it out

was a man called Aristarchus.

If you look at the Moon,
there's a bright crater,

and it's called Aristarchus,
named that way

to help us remember the man who
told us the size of the Moon.

So, how did Aristarchus do it?

The answer is that
he simply observed

its passage through the sky.

And he calculated
that it took one hour

to cover the distance
of its own diameter.

Once he'd worked that out,
he had to find a way

to make that figure relevant
to the size of the Earth.

Aristarchus realized
that he could use

a phenomenon called
a total eclipse.

And a total eclipse of the Moon
is a common thing.

It happens once or twice a year,

when the Moon passes
through the Earth's shadow.

He discovered that
the Moon took about 2.7 hours

to cross through
the Earth's shadow.

And so, he then knew
that the Earth's shadow

was 2.7 times larger
than the Moon itself.

Aristarchus's calculation
showed that the Moon was

3,000 miles across in diameter

and we now know
that the true figure

is just over 2,000 miles.

What this does is, it extends
the reach of measurement

out above the Earth's atmosphere
and into space.

He says that the universe
is a place

that scientists can
explore as well.

Once we know the size
of the Earth and the Moon,

it's possible for my volunteers

to take the next step and find
out how far apart they are.

But first, a guess.

I think it's closer.
I think it's about there.

That is what I was gonna do.

I was gonna put them
close, I think.

Closer than further.

I think that it's
a bit further away.

Wow, that far?
Going big.

I put this as my guess.

Ok.

So, how can
we find out for sure?

This evening,
there is a full moon.

That is the final
clue they need,

to think like Aristarchus.

Maybe we take the Earth

and put the Moon in front of it,

until we cover up the Moon.

Same size?
Same size.

Ok.

Take it till we
lose sight of the Moon.

Cat has the answer.

I'm looking at
the real moon in the sky

and the little moon that we have

and I'm thinking,
"well, they're the same."

So, maybe we need to black out
the real moon in the sky.

Closer. Closer.

A little...
A little closer.

All right.
I say that's it.

Is that it?
Yeah.

So, you were right.

The Moon is pretty
far from the Earth.

Yeah, a lot farther
than we thought.

When the scale moon is
just the right distance away,

it will cover the real moon
perfectly.

That's how you find
the distance.

In the desert, the scale models

of the Moon and Earth
are 6 feet apart.

Up in the sky, the real moon
is about 240,000 miles away.

It worked.

I'm not a scientist and to be
able to just do that off a whim

and it just came to me,
that was... that was incredible.

By measuring the Earth
and our distance to the Moon,

we've taken our first step
out into space.

But to find out where we truly
are in the universe...

Got it?

The next step is
to figure out our place

in relation to the brightest
object in our sky... the Sun.

Today, we know it is nearly
900,000 miles in diameter.

But again, people don't realize
how big that really is.

Whoa.

That's the Sun.

That's massive.
It looks so big.

This is the Sun
at the same scale

as our tiny
Earth and Moon models.

Go this way.

Ok.

Uh, this thing.

At first, when we
tried to lift it,

we could barely pull the...
Pull the model out.

It's giant.

Careful. This is
really to scale?

And then we start unrolling it

and it just keeps going
and going and going.

'Cause I just wanted
to fill it up with air

and see really how big it was.

It just seemed like
it was more and more fabric,

more and more, just keep
coming, it kept coming.

Oh, wow.

Right.

Let's blow this bad boy up.

I was just thinking,
"wow, how big is this sun?",

compared to this tiny Earth
that I had in my hand.

So, if this is the Earth,
then this is the Sun.

The Sun is almost 110 times

the diameter of the Earth.

Now, the next big question.
On this scale,

what is the distance between
Earth and the Sun?

So, how far do we
have to move that model

to get the distance

and how are we gonna
get the distance exact?

I don't know.

Much like it was with the Moon,

the key to answering this
question is an eclipse.

But this time,
it's a solar eclipse.

When the Moon passes
in front of the Sun,

seen from the Earth,
the Sun and moon

are exactly the same size.

So, they should be able
to find the distance

by creating an eclipse
on their model.

In the solar eclipse,
we can't see the Sun at all.

So, when this sun disappeared,
you'd have a solar eclipse.

Boom.
There we go.

So, all we need is
a solar eclipse.

Yeah, exactly.

We jump in the truck
and we just go.

We... we go in the desert and we
just drive, drive, drive.

How far do they need to drive?

I think that's about it.

They decide to stop
400 meters from the Sun.

All right.
Let's see.

The Moon right there.

To make the tiny moon
eclipse the Sun,

it always has to be
6 feet from the Earth.

Ok, so, I've got the Earth here.

All right.

So, we know this distance

and now I'm going to see

whether the Moon is
the same size as the Sun.

It's actually a bit smaller,

so, we have to go a bit
closer to the Sun.

All right, let's move it.

Let's do it.

Do they need to be
closer or further away?

Let's try here.
About there?

Yeah, I think so.

The Sun is still bigger.

- Really?
- Yeah.

The Sun's still
bigger than the Moon?

Yeah. That means we
would go that way.

I'm having a dumb stroke.
I'm having a dumb moment.

Let's go back.
All right.

I think we all felt a bit silly.

We're walking across the desert.

What were we thinking?

How much further
do you guys think?

I'm saying check it.

Check it.

Bam, right there.

Ok, ready, we look.

Oh, we got it.

- Yeah.
- We got it.

Yeah.

They've done it.

On this scale, the Sun is just
under half a mile from Earth.

Up in space, the distance
is 93 million miles.

To see it in perspective, I
mean, our Earth was only so big

and we had to take it across the
desert in order to show distance

and I mean, that just
shows how... How small we are.

Our volunteers have figured out
the distance between

the Sun, moon, and Earth using
nothing more than 3 round balls

and a little bit of logic.

But now we need to find out

where we are on
a much larger scale.

If we know the Sun is
93 million miles away,

how big is the entire
solar system?

The ancient astronomers knew
from observing the heavens

that there was more
to the universe

than the Earth, Moon,
sun, and stars.

They identified
5 points of light

that moved in a different way
from the stars.

These are the planets.

Here on our scale model,
Mercury is closest to the Sun.

As we head further
into the solar system,

we can see Jupiter
on the horizon.

Viewed from above, we can see
all 8 planets aligned.

Neptune is 9 miles
away from the Sun,

or nearly 3 billion
miles in space.

And the entire solar system is
180 billion miles side to side.

We know we have
all the planets, the stars,

the Sun, but when you see it
for yourself in a perspective,

our solar system is much bigger
than we think it is.

We have now found out the true
scale of our solar system

and our place within it.

But where is our solar system?

To find out, there was
an even greater question

which had to be solved before

we truly understood
our place in the cosmos.

Well, working out
distances is all very well,

but you realize pretty quickly
that you need to know

how things relate to each other.

Look at the stars and you'll
see that they move.

So, it's natural
to conclude that

the stars are moving around us.

In the 16th century,

a Polish astronomer
called Copernicus

dared to challenge
the traditional assumption

that the Earth is at
the center of the universe.

Copernicus realized
the common sense view

of the universe isn't right.

And he started to wonder whether
something else is going on.

Copernicus had two big theories.

Firstly, the Earth is
spinning like a top.

And secondly, the Earth is not

at the center of
the solar system.

In fact, the Sun
is in the middle.

And we are spinning around it...

Like all the other planets.

He knew there was
something beautiful

about the idea of
a sun-centered universe.

It seemed to him simpler.

Although his theory
was more logical,

Copernicus faced
a serious problem.

Wow, what is this?

This looks so cool.

And this machine will
help our volunteers figure out

that the problem is all
a matter of perspective.

How does it move?

I think someone has to push it.

That's my job.

Your job.
You're gonna push?

You guys get to be
the test pilots.

All right.

Whoo!

Wow. Ok.

So, are we spinning,
or is the background spinning?

From where I'm sitting,
you're not spinning.

If you are on a planet
that is turning slowly,

so that you can't feel the spin,

how can you be sure that
the Earth is spinning,

and not the universe?

That's the problem
Copernicus faced.

If we're Earth
and we're spinning,

how do we tell it's
actually us spinning?

Oh, that is such
a difficult problem.

I mean, you have to
have a pinpoint that

is not part of the universe
and not part of the Earth.

The only way
to see the Earth spinning

is to be at a fixed point
out in space... just like Jim.

500 years ago, space travel
was impossible, of course.

But in 1609, an Italian scholar
called Galileo

invented the next best thing...

The astronomical telescope.

Galileo Galilei is perhaps

the founder of modern science.

His telescope was
going to revolutionize

our view of the universe.

Galileo pointed
his telescope at Jupiter

and he sketched out
what he observed.

There were moons
spinning around it.

This was immediate proof that

not everything moves
around the Earth.

And when he looked at Venus,
he made a staggering discovery.

He sees Venus as a disc,

but then the disc
is changing in size

and it's changing in shape.

It becomes a thin crescent.

He found that just as
the Moon waxes and wanes

as it moves around the Earth,

Venus does the same thing
as it rotates around the Sun.

Galileo comes with the proof,

that the Sun was at the center

with the planets going
around the Sun.

Everybody can build a telescope,
look at the phases of Venus,

and there is
no other conclusion.

That's a fact.

Galileo proved
that Copernicus was right.

The Earth is a ball
circling the Sun.

But to prove it was spinning

would take
a wonderful revelation.

As a child, I used to go
to London's science museum,

where I could witness this
revelation with my own eyes.

For me, it's one of the most
striking demonstrations

in the history of science.

The best experiments
are incredibly simple

but point us to profound truth.

And that's what we've got here.

It's called foucault's pendulum
and it's really very simple.

It's just a very long pendulum

swinging under
the influence of gravity.

And the first of these
large-scale pendula

was set up in 1851 by
a guy called Leon foucault,

who wanted
a simple demonstration

that the Earth was turning.

Foucault set a pendulum moving

in front of a crowd for a day.

And what they saw
was astonishing.

Over the course of the day,

the pendulum's direction
of swing would move,

a bit like the hands of a clock.

What was the source
of this rotation?

Back in the desert,
we can see a direct parallel

between this machine
and the pendulum.

To show it, all we need
is a ball.

So, if I throw a ball to you,

are you going to catch it?

Ready?
Yeah.

Does it look like the ball's
curving when you throw it?

Yeah. Yeah.

That's crazy.

The ball travels
in a straight line.

He's right... the line
is dead straight.

Ok, cat, you ready?

The ball only
appears to be curving

from cat and joy's perspective,

because they are spinning.

- You ready?
- I'm ready.

It absolutely demonstrated

that they were turning
around on an axis

and that everything was
not turning around them.

It's the coolest thing ever.
I love it.

So, what you see
depends on where you are.

And it's just the same with
the pendulum in the museum.

The best way to think
about this experiment

isn't actually
to be sitting here.

It's to imagine you're
on the pendulum itself.

You just go backwards
and forwards all day long.

What you will have seen
is the Earth is rotating

underneath this pendulum,
which continues going

backwards and forwards
and backwards and forwards

regardless of what's
happening underneath it.

With his pendulum,
foucault convinced the world

that Copernicus
and Galileo were right.

And anyone can see the Earth
turning with their own eyes.

I love it because it's so simple

and yet it demonstrates
two fundamental principles.

One is the idea that
the Earth is turning.

And the second thing
it demonstrates

is that perspective matters.

Where you are changes
how we see the universe.

Our volunteers have discovered

how we are just one of many

spinning balls orbiting our sun

in a planetary community
called a solar system.

But now I want to take us
further into the cosmos

and explore where we are
in relation to the stars.

On a clear night, there are
3,000 visible stars.

But how far away are they?

By the 19th century,

telescopes had become
powerful enough

to hone in on individual stars.

And in 1838, German astronomer
frederich bessel

was able to make
a momentous calculation.

Bessel knew that because
the Earth goes around the Sun,

it must travel huge distances
in space throughout the year.

584 million miles, to be exact.

So, he decided to observe
a star called 61 Cygni

at different times of year.

And that meant he could see it

moving slightly
against the background.

Then, by using trigonometry,

bessel could triangulate
the star's position in the sky

and find the distance.

Using this method,
bessel worked out that

61 Cygni was around 67 trillion
miles away from Earth.

This was far greater
than any distance

we had encountered
in our solar system.

So, a new unit of measurement
was needed

to take us to
interstellar space.

It's called the light year.

It's the distance that
light travels in one year.

Whizzing along at 186,000
miles a second.

That's around 5.8
trillion miles a year.

61 Cygni is found to be
about 11 light years away.

To try and understand such huge
distances, I want to explore

what the speed of light
looks like on our scale model.

How fast is the speed of light?

Well, it's fast, right?

It takes sunlight
8 minutes and 20 seconds

to travel from the Sun to Earth.

So, in our model, the speed of
light is the speed needed

to get from the Sun
to the model Earth

in 8 minutes and 20 seconds.

How fast is that?

We know it takes 8 1/2 minutes,

so, how fast do we need to move

to get from our model
sun to our model Earth?

Let's be the light.

Let's walk 750 meters

and time it and see
how long it takes.

All right.
All right.

I'll get the watch.

Let's go.

On the scale, every
foot that my volunteers travel

represents over 40,000 miles.

How much time
have we been walking?

40 seconds.

Only 40 seconds?

Yeah.

And we've gone pretty far.

I mean, I can see
the Earth from here.

How fast is the speed
of light on this scale?

Almost there, almost there.

Passing the Moon.

Hello, Moon.

And bam.

What did you get?

8 minutes, 35 seconds.

Wow.

So, we pretty much walked

from the Sun to Earth
in the speed of light.

Even though it's the
fastest speed in the universe,

the speed of light on this scale
is just over 3 miles per hour.

That's walking pace.

So, light isn't as fast
as we perceive it to be.

I can walk the speed of light?

It's fast but it's not fast.
It's crazy.

In the entire universe, light
appears to travel really slow.

Wow.

It's a strange paradox.

Although the speed
of light is fast,

distances in space are so huge

that even one light year
is not very far at all.

It's such a revelation,
but then it alters,

it just alters your thoughts,

and I have to sit...
I have to sit in a quiet place

and wrap my head
around it for a while.

If it takes 8 minutes

for my volunteers to reach
their model Earth,

imagine how long it would take
to get to our nearest star.

It's called proxima centauri.

On our scale model, it would be
126,000 miles away from the Sun.

So, our volunteers
would have to walk

halfway to the real moon
to reach it.

In space, the total distance
is 4.2 light years.

I'd have to walk for
4.2 years continuously

to get to my nearest star.

If I was gonna shrink that down

for the purpose
of demonstrations,

well, our scale model's
gonna be like a speck of sand.

Even on this scale,

distances have now become
too large to comprehend.

We need to shrink our
model sun from this...

To this.

Wow.

This is our sun?

From that big, giant sun
we had earlier, is now this.

Yeah.
That little dot.

Even on this tiny scale,

the distance between the tiny
sun and our nearest star

would be 17 miles.

We can try and get
a grip on this

if we light a flare 17 miles
away across the desert.

There it is.

Whoa.

That is incredible.

To see the nearest star
so far away,

when our sun is that small,
was just amazing.

It made me think about
all the stars in the sky.

These are the things that
feel so familiar to us,

but yet, we don't know
anything about them.

After centuries of
observations, we now know that

our sun and its nearest
neighbor, proxima centauri,

are part of a small
community of 33 stars,

all within 15
light years of Earth.

And this system
sits in a network

of an estimated
300 billion stars

called the Milky Way.

And until recently,
astronomers believed

that this galaxy was
the entire universe.

That was the whole answer to
the question "where are we?"

Then in the 20th century,
a new generation of telescopes

allowed us to explore
new formations,

and they seem to be
much further away.

People had been seeing different

smudgy patches of light
on the sky

and they struggled
with what these

faint smudges on
the sky actually are.

Enter Edwin Hubble,

20th-century
American astronomer.

Using this telescope at the mount
Wilson observatory in California,

he made a sensational discovery.

He realized that these smudges

were millions of
light years from us.

It was Edwin Hubble's discovery

of the distance to
these smudgy patches

that indicated that indeed,
these were other galaxies,

just like the Milky Way,
at great distances from us.

Hubble found that the sky was

studded with distant galaxies,

giant collections of stars
far beyond our own galaxy.

So, this just
shatters everything.

It shatters the small Milky Way

and it shatters the notion that

the universe can be
contained in the Milky Way.

Now these distances are just
getting bigger and bigger.

Distances are indeed
becoming astronomical.

Our next one is 2.5
million light years away.

That's the distance
between the Milky Way

and our nearest galaxy,
Andromeda.

Now that we are
talking galaxies,

it's time to introduce
a new scale model.

Our next challenge
is pretty simple.

If we could fit our galaxy
on a smartphone

and Andromeda on a tablet,

how far apart would they be?

So, these are our galaxies.

This is the Milky Way

and this is our closest
galaxy, Andromeda.

The Milky Way is

100,000 light years
side to side.

With that information, I want
my volunteers to work out

the distance between
the two galaxies.

So, our Milky Way is

100,000 light years wide

and Andromeda is 2.5
million light years away.

So, on this scale,
comparing this to this,

how far away is this galaxy?

So, this is 100,000
light years across

and there's 10 times
that is a million,

and so, that's 2.5 million
light years away.

So, that would make...

25 of those.

25 of these.

Shall we measure it?

1, 2, 3.

25.

That's it?

That's it.

And that's our nearest galaxy.

The Milky Way and
Andromeda are just the start.

They are surrounded
by dozens of galaxies

in the local
galactic neighborhood,

and it doesn't stop there.

In 1990, the Hubble space
telescope is launched.

After a decade of observations,
this picture is released,

showing thousands of galaxies
which stretch away

into the far distance, for
up to 13 billion light years.

And this is just
a tiny part of the sky,

like looking at a postage stamp
from 100 feet away.

My brain will never
get around this.

This is gonna take me weeks.

The rest of my life maybe.

In the desert,
our volunteers have figured out

distances around the Earth
to our Sun.

It's like perfect right now.

And across our solar system.

The thing that will
stick with me the most

is just how tiny we are.

Then out into
our galaxy and beyond.

There it is!

In the grand scheme of things,
we are infinitely small.

And now, back on Earth,

we return to our first question.

Where are we?

We have learned that our planet

is a little sphere
orbiting a star...

In a modest neighborhood
called the solar system.

We are surrounded by a local
group of a few dozen stars,

up to 50 light years distant.

And we all occupy one little
part of a spinning arm,

in a medium-sized galaxy
known as the Milky Way.

Along with more than 50 others,

we form a local
group of galaxies

10 million light years across.

And together,
we inhabit one corner

of a vast collection
of galaxies,

known as the laniakea
supercluster.

It's like a huge galactic city,

filled with hundreds of
thousands of galaxies

similar to our own.

Grouped with many more
millions of clusters,

they form gigantic arms which
stretch through the cosmos.

The largest structures
known to humanity.

And this is just
one small corner

of the observable universe...

Which is billions of
light years, side to side.

Even though the distances
are unimaginable,

the fact that most people
can understand

such a universe does exist

is a remarkable feat
of the human mind.

So, now I hope you are
beginning to realize

that with a little bit
of thinking,

you have the genius
to figure out where we are.