All language subtitles for The universe S07E01 How Big, How Far, How Fast

Male narrator: In the beginning,
there was darkness,

and then, bang,

giving birth to an endless
expanding existence

of time, space, and matter.

Every day, new discoveries
are unlocking the mysterious,

the mind-blowing,
the deadly secrets

of a place we call
The Universe.

The numbers of the universe
boggle the human mind.

- In the observable part
of the universe,

there is something like
100 billion galaxies,

each with billions of stars.

- The Andromeda Galaxy is about
2.5 million light-years away.

- The Earth is orbiting the Sun

at a speed
of about 66,000 miles per hour.

Narrator: Most of us give up
even trying to comprehend

such titanic sizes, distances,
and speeds.

But are there ways

to bring the sweep of the cosmos
down to Earth

TO help us understand how big,
how far, and how fast?

Planet Earth,

for all its wide expanses,

deep seas,

and massive mountains,

amounts to a speck of dust

when stacked up against
the immensity of the cosmos.

- The observable universe
contains of order

100 billion galaxies.

And then each galaxy,
like the Milky Way,

contains of order
100 billion stars.

- The numbers quickly get up
into the millions

and then the billions
and even the trillions.

And by then, we've really lost
all sense

of what that really means.

Narrator: The human mind
is finely tuned

to deal with the scale
of day-to-day experience.

The brain can understand
traveling 50 miles in a day.

But what about 500,0007?

And a person may know
what it's like

to move at 100 miles per hour.

But what about 100 million?

- Numbers like millions
and billions

and certainly trillions

are very hard for most people
to imagine,

because, frankly, most of us
don't have billions

or trillions of anything.

Narrator: So how can we
ever know the universe

if our brains can't really
comprehend its massive scale?

- Doing scale models
of objects in the universe

is really helpful,
because it brings them down

to sizes that we can imagine,

that we do see in our normal,
everyday lives.

Narrator:
We can start by cutting

the biggest players
of the night sky—

Planets, stars, and galaxies—

Down to an earthly scale.

There are two ways
to evaluate size.

We can measure dimensions—

Meaning height,
length, and width—

Or calculate bulk,
also known as mass.

Bigger doesn't always mean
more massive.

- Let's say a balloon has

the same volume
as a bowling ball.

But the bowling ball has
more mass

because it's denser.

It's just got more mass crammed
into that same volume.

Narrator: To help get a grasp
on some of the immense masses

floating around our universe,

astronomer Laura Danly visits
a monster truck rally...

a place where objects of hugely
differing masses often collide.

- We've got everything
from a small toy truck

to the giant monster truck...

and that gives us
a range of mass

that will help us understand
how massive things are

in our solar system
compared to each other

and how massive our own Sun is
compared to some other stars.

Narrator: We begin
the comparison with Jupiter,

known as the king of planets,
and for good reason.

Its mass amounts to more than
4 octillion pounds.

That's a 4
followed by 27 zeros.

Put another way, it would take
more than 300 Earths

to match Jupiter's mass.

But even that is measly
when compared to the Sun.

- The Sun is by far
the most massive thing

in our solar system.

It's about 1,000 times
more massive than Jupiter,

the biggest planet.

Well, by comparison, this car
behind me is about 3,000 pounds,

and this little toy truck is
about 3 pounds.

So that's
about the same difference

between the Sun and Jupiter.

Narrator:
It's a crushing difference,

as 3,000 pounds
make perfectly clear.

But remember, this is
a monster truck rally,

and the junk car
representing our Sun

may regret picking on
little Jupiter.

- The Sun is the most massive
object in our solar system,

but it's not the most massive
star in the galaxy.

There are a lot of stars
more massive than the Sun.

Narrator: To envision
the disparity between the Sun

and a more massive star...

let's keep the 3,000-pound
junk car as the Sun

and put it up against
a 10,000-pound monster truck

representing a star
some 75 light-years away.

- The difference between
the monster truck and the car

is about the same difference
as a star called Regulus—

The bright star
right in the middle of Leo,

about 3 1/2 times as massive
as our Sun.

Narrator: Three times more
massive may not seem like much,

but don't forget we're now
pitting galactic giants

against each other.

[engine revs]

- Well, that was quite a shock.

But as you can see, three times
the mass difference

makes a difference.

If we could somehow bring
Regulus here

and have it sit on top
of the Sun,

that's about
the same comparison.

Narrator: But even
monster truck-sized Regulus

can't stack up
to the immense mass

of the true titans
of the universe.

- The most massive star we know
orbits around the Milky Way—

A little companion galaxy called
the Large Magellanic Cloud—

In the middle of a nebula called
the Tarantula Nebula.

That star has a kind of
boring name—R136a—

But it's still
a very massive star.

Narrator. R136a is a young star
about a million years old.

Its surface temperature is
70,000 degrees,

about 7 times hotter
than our Sun.

Before 2010,
stars were thought to form

no bigger than 150 times
the mass of the Sun.

But new discoveries
have doubled that limit.

- We think R136a
is probably about 250,

maybe as much as 300 times
the mass of our Sun.

Narrator: To represent
this massive star,

you need
a truly monstrous truck.

This monster
is 100 times heavier.

But extreme mass also comes
in small packages,

where density takes
the force of gravity

into radical territory.

The greatest massive
bang for the buck

we can see in the universe

comes from a stellar object
known as a neutron star.

A neutron star is the leftover
core of a supernova explosion,

with its mass packed
astoundingly tight.

- It's got 1 1/2 times
all of the mass of our Sun

crammed into a volume
of about 10 miles across.

If you crammed one monster truck

down into the size
of a sugar cube,

that would not be anywhere close
to as dense as a neutron star.

I'd need
10 million monster trucks

crashed down into the size
of a sugar cube.

Narrator: Stack these 10 million
monster-truck sugar cubes

ten miles high and wide,

and you've got yourself
a neutron star.

- Neutron stars are just
bizarrely extreme objects.

If you were to try to land
on a neutron star,

it would be
absolutely impossible,

because you would find that
on the neutron star,

you weigh about 5 billion times
more than you do here on Earth.

Narrator:
But mass isn't everything

when it comes to finding out

just how big
the biggest stars can be.

The universe is also filled
with titans

that take up
unimaginable amounts of space.

Some of the tiny pinpricks
of light we see from Earth

are actually stars big enough to
swallow our entire solar system.

Can the human mind
even comprehend

the largest star in the galaxy?

We're bringing the sizes,
speeds, and distances

of our vast universe
down to a scale

the human mind can comprehend.

The biggest thing
in our solar system by far

is the Sun.

In terms of sheer mass,

it weighs over 300,000 times
more than the Earth.

But in terms of volume,

it's also the solar system's
physically largest object,

at 870,000 miles across.

- So the Sun is really big
compared to the Earth.

It's 109 times as wide
as the Earth.

That actually means
that over a million Earths

could fit inside the volume
of the Sun.

It's really big.

Narrator: But as enormous as
the Sun is in earthly terms,

our home star seems puny
when stacked against

our galaxy's lineup
of stellar mammoths.

With strange names taken
from history and science,

they push the envelope
of what it means to be a star.

Consider them in turn:

Vega...

Bellatrix...

Epsilon Can is Major is...

Dubhe...

Aldebaran...

and finally,
the super-enormous Betelguese...

and VY Can is Major is.

- Oh, wow.

Narrator:
Astronomer Alex Filippenko

attempts to bring them
down to Earth

in an airplane hangar.

- We're here
in this airport hangar today

in order to try to illustrate
the relative sizes of stars,

in particular big stars.

We're going to inflate
some balloons,

and even some really big
weather balloons,

and show them in comparison
with the Sun,

which we've scaled down
to the size of a bowling ball.

[air hissing]

Narrator: The bowling-ball Sun
is 8 1/2 inches across,

which would make the Earth
no bigger than a tiny bead.

- My two assistants are
balloon experts.

They know how to inflate
balloons with helium

and tie them off,

and they know how much
to inflate them.

So they're going to inflate
these different balloons

to different sizes.

Narrator:
Inflating the balloons

will take us
on a scaled-down tour

of the Sun's big, bigger,
and biggest brothers.

First stop: the star Vega.

Located
in the constellation Lyra,

Vega is one
of the five brightest stars

in the night sky.

It glows blue-white because
it burns hotter than our Sun.

- Okay, so I've got
my bowling-ball Sun here.

Guys, how big is this balloon?

- Let's check it out.

It's about 2 feet.
- Right about 2 feet.

- 2 feet, so that's—that's
about 2 1/2 times the size

of the bowling ball.

So that's like the star Vega.

It's a bluish white star,

25 light-years away,

very bright star in the sky.

Narrator: Next up is Bellatrix,
a star in Orion the Hunter...

the brightest constellation
in the sky.

Well-known stars pinpoint
its torso and belt.

Another blue giant, Bellatrix is
at Orion's right shoulder

and shines 240 light-years away.

- So here's a bigger balloon.
What's its size?

- This is 4 feet.

- 4 feet, so that's about
5 1/2 times the size

of my bowling ball—
my Sun.

So this is a bigger star.
It's kind of like Bellatrix.

Narrator: Bigger than Bellatrix
is the hot blue star Adhara,

also known as
Epsilon Can is Major is.

Can is Major is a constellation
whose name translates

as "the great dog."

- Wow, now here's a big star,
huh?

- This one is 12 feet.

- This thing is 17 times wider
than the Sun.

That's kind of like the star
Epsilon Can is Major is

in the constellation
Can is Major.

That's the same constellation
that Sirius is in.

Sirius is the brightest star
in the sky,

but Epsilon Can is Major is is
430 light-years away.

If it were at the same distance
as Sirius,

it would appear
15 times brighter.

Narrator: Almost twice as big as
Epsilon Can is Major is is Dubhe,

a giant star on the lip
of the Big Dipper,

120 light-years away.

- Wow, cool.

Well, here I see
an even bigger balloon.

What's its diameter?

- Let's see.

21 feet.
- 21 feet.

So that's about 30
of my bowling-ball Suns.

In fact, that's about the size
of the star Dubhe.

That star Dubhe is different
from the others that we've seen.

It's what's called a red giant.

It's got kind of
an orange color.

It's cooler than the blue-white
ones that we've seen previously.

Narrator. Amazingly, stars come
in larger sizes still.

And even an airplane hangar

isn't big enough
to contain them.

Here's where we have to place
Aldebaran,

a monster star known
since ancient times

and once thought to be a sign
of riches and honor.

- This balloon is
about 32 feet across.

Now, that's roughly 45 times
bigger than this bowling ball

which represents our Sun.

Now, this balloon then is about
the size of the star Aldebaran,

a red giant in Taurus the Bull.

It's about 65 light-years away,

and its true color is
roughly orange.

Narrator. Now even the biggest
balloons fall short

in representing the size
of the galaxy's biggest stars.

Betelgeuse, for instance,
is another star in Orion.

650 light-years away,

it is a thousand times
the size of the Sun.

- Betelgeuse is so large
that its radius would extend

roughly to the orbit of Jupiter.

So if Betelgeuse was actually
in the solar system,

then all of the eight planets

would be completely
either destroyed

or totally too hot
to be habitable.

Narrator:
But the largest known star

is a beast by the name
of VY Can is Major is.

By some estimates,
it extends

to 2,000 times the diameter
of our Sun.

- That is a truly
gargantuan star.

If there were
a commercial airplane

flying just outside
VY Can is Major is,

it would take it about
1,200 years to fully circle it.

Narrator. Any object
on this enormous scale

seems truly alien
to the human mind...

an intimidating answer
to the "how big" question

about the universe.

No less discomforting is
"how far?"

Because distances between
planets, stars, and galaxies

stretch beyond
all human experience.

- So a really great way
of bringing it home

is to scale everything down
to a more human scale.

We're better at understanding
the relative sizes of things

than abstract absolute numbers.

Narrator: Take the Moon.

It lies a little less than
250,000 miles from Earth.

You might think this isn't
all that far.

Well, think again.

- Imagine if I shrank the Earth

down to about the size
of a basketball.

So if the Earth was about
the size of this object here,

I would actually have
the Moon be

about the size
of this tennis ball.

So the next question
you might ask is,

"Given the relative sizes
of these things,

how far apart are they
going to be from each other?"

To show you, I'm actually going
to need some help.

So Johnny is actually going
to hold the Earth for me

while I actually take the Moon
and measure out

how far away it needs to be.

So here goes.

1 foot, 2 feet...

all the way back,
we're already at 10 feet.

Probably go even more.

It's already past 15.

We've got to go much further.

And here we are at 21 feet.

That's actually how far away
the Moon is from the Earth

in our scale model.

Narrator: At 239,000 miles,

the Earth-Moon distance
has now become familiar to us,

because of Apollo missions
to the Moon.

This is one of the few
astronomical spans

we can readily understand.

In six manned moon landings,

we learned that the travel time

was a little more
than three days.

And the lunar commute
has become a part

of our collective knowledge.

- Engine stop.

Okay, Houston,
the Challenger has landed.

Narrator:
But beyond the Moon,

the solar system extends
to distances so vast,

again, our limited minds
aren't really up to the task.

But what would happen
if we literally brought

all the planets down to Earth?

Narrator: It can be overwhelming
to consider how big, how far,

and how fast everything is
in our universe.

Even in our solar system,

the distances are almost
unimaginably vast.

That's why we're shrinking
our solar system

and bringing it down to Earth.

- Imagine if we took
the 870,000 miles

of diameter of the Sun

and shrank it down
to the size of a bowling ball.

What would that do
to the planets?

Well, we'd have to shrink them
down to sizes that we have here.

So we have the eight planets
of the solar system lined out,

starting with Mercury
all the way out to Neptune.

So in this scale model,
our Earth, our home,

is this tiny little bead,

while the Sun is
this bowling ball.

Narrator: These bead
and marble planets

may be to scale
with the bowling ball Sun,

but the distances
between them aren't.

To demonstrate that,
physicist Clifford Johnson

is going to walk the length
of this miniature solar system

laid out along a runway.

- I have Johnny here,
who's going to help me measure

the distances
with this surveyor's wheel.

Okay, so let's go and explore
the solar system.

- All right, let's do it.

Narrator. Each foot
in this scaled-down solar system

represents 1 million miles

in the distances
between the planets.

[wheel clacking rhythmically]

- And here we are at Mercury.

- And that's 36 feet.

- In reality, it's actually
about 36 million miles

away from the Sun.

It's amazing just how far

the very first planet
of the solar system is

from the Sun.

So now let's go on
to the second planet.

- Here we go.

- So here we are at Venus.

- And that's 67 feet.

- So this bead
representing Venus

is about twice as far
from the Sun as Mercury is.

It's actually, in reality,
about 67 million miles away.

[clacking of wheeled gauge]

And here we are at the Earth.

- And that's 93 feet.

- We have the Earth here
represented by this marble.

And, in fact,
it's, in reality,

93 million miles away
from the Sun.

The way the bowling ball looks
in terms of the size from here

is about the size
the Sun appears in our sky.

We have this blue bead
representing the Earth.

And about 2 1/2 inches away,

we have a much smaller bead
representing the Moon.

Narrator. Remember
that on a different scale,

with Earth the size
of a basketball,

the Moon was 21 feet away.

To bring the whole solar system
into the picture,

we've had to scale down
the Earth-Moon distance

to mere inches.

- This tiny distance
between the Earth and Moon

is the limit so far
of manned exploration of space.

Hopefully, we'll do a lot better
in the years to come.

Narrator:
On our runway,

Mars orbits
another 49 feet away,

or almost 142 million miles
from the Sun.

The distances beyond Mars are
about to get much, much larger.

- Here we are—Jupiter.

- We're at 484 feet
from the Sun.

- That's actually three times
as far from the Sun as Mars is.

Narrator: With all this space
between these tiny marbles,

it's a wonder we can see
the planets from Earth at all.

- It tells us that the Sun is
incredibly bright

so that the light from the Sun
can go out to these bodies,

reflect off them,

and then come back
to here on Earth

for us to see them.

Okay, onwards and outwards
to Saturn.

- All right, here we go.

Narrator:
Our two space explorers

find Saturn 886 feet
from the Sun.

- In fact, Saturn,

at 886 million miles away
from the Sun,

is almost twice the distance
from the Sun

that Jupiter is from the Sun.

So we've come
a huge extra distance,

and we're not even done
with the solar system yet.

Narrator: At 1,800 feet,
the scaled orbit of Uranus

stands twice as far as Saturn,

1.8 billion miles from the Sun.

- I can hardly see
the Sun back there.

And I can actually hardly see
Neptune in the distance,

which is our next stop
on our journey.

Shall we go?
- Let's go.

- Jeez, that's far.
-Yep.

- [laughs]

And here we are—Neptune-

the last of the planets.

- 2,798 feet from our Sun.

- That from our model translates
into the real-world distance

of almost 3 billion miles

that Neptune is away
from the Sun.

This far out,
a planet takes a long time

to do an orbit around the Sun.

The Neptunian year is about
165 of our Earth years.

In fact, only one of those
Neptunian years has passed

since Neptune
was actually discovered.

Narrator:
Viewed on this scale,

it's a wonder the Sun's gravity
has any effect at all.

And there's still more to
the solar system beyond Neptune,

including smaller bodies,
like Pluto...

and then,
nearly a light-year away,

clouds of dark icy comets.

If the space between the planets
in our solar system

strains human comprehension,

then the vast distances
between stars and galaxies

totally overwhelms it.

That astronomers even know
how far away stars are

is a mystery to Nora
from Brooklyn, New York,

who wants to...

- Nora, that's actually
a pretty complex question.

For the most nearby stars,

we look at how their positions
in the sky change with time

as Earth orbits the Sun.

For more distant stars,
or stars in other galaxies,

we measure how bright
they appear to be,

compare that
with their known power,

and thus determine
their distance.

Narrator: They are distances
so immense that "how big"

and "how far" are questions
to challenge

anyone's power of comprehension.

But the magnitudes
of the universe

also extend to speed.

What scientists have discovered
is that the universe

is a super-velocity racetrack

where even giant planets move
faster than speeding bullets.

We've seen how big
and how far things are in space.

Now we're going to see how fast.

To do that, first,
we have to understand

the celestial measuring stick
known as the light-year.

Just like it sounds,

one light-year is the distance
light travels in one year.

That amounts
to about 6 trillion miles.

But that doesn't help us
understand

how fast light speed itself is.

- The speed of light is
really fast—

About 186,000 miles per second.

Now that's hard to conceive
without an example.

Imagine light were bouncing
back and forth

between Los Angeles
and New York.

It could do 38 back-and-forth
bounces in one second.

Narrator: In an effort
to chase down the concept

of the speed of light,

astronomer Greg Laughlin

teams with firearms expert
Michael Voigt

to demonstrate some of the
fastest moving objects on Earth.

[gunshot]

- The way we're going to do that
is to compare the speed of light

to the speed of something that's
really fast here on Earth,

which are bullets.

- We've got a target downrange,
so when it hits it,

you'll hear that ding
on the end of it.

And you can kind of see how long
that actually takes.

This is a .204 Ruger.

This is the fastest
commercial cartridge

on the planet right now.

- We've got a 300-yard travel,

so I'm really going to try
to get a sense

of the time that it takes

for that bullet
to travel downrange.

So let's see how that works.

[gunshot]

- Nice shot.

[gunshot]

- Boy, I couldn't get any sense.

As soon as I pulled
the trigger—boom—

It hit the target.

No sense at all
of the travel time.

[gunshots]

Narrator:
Because it's so difficult

for the human senses to perceive
the speed of these bullets,

Mike sets up a highly accurate
timing device

known as a chronograph.

- So this is the unit
that the timer's actually in.

Inside, it's got a clock.

- Okay, it looks like
the chronograph's ready here.

- All right.

Let's put a couple rounds
through here,

and we'll see how fast
this ammo goes.

And what do we have?

- Wow, so that was 4,297 feet
per second.

So that's about 3,000 miles
per hour.

- Pretty quick.
- Pretty quick.

It's a little less than a mile
per second.

That's roughly four times
the speed of sound.

So, I mean, I'm impressed.

But that pales in comparison
to the speed of light.

In the time that it took
for those bullets to go

from the muzzle of the gun

all the way downrange
to hit the target,

during that time,
light has enough time

to go all the way around
the surface of the Earth

from Los Angeles to Paris
and then back

in that same amount of time.

Narrator. Moving at
670 million miles per hour,

light completely demolishes
any earthly experience of speed.

- That really doesn't mean
very much to me,

because the whole distance
of 670 million miles

is much larger
than any kind of distances

that we normally deal here
with on Earth.

Narrator: The speed of light
and the speed of our world

are so vastly far apart,

we have to take light
and slow it down

to really understand
the difference.

For that, we go back
to the speeding bullet.

At 3,000 miles per hour,

we can barely perceive
its speed.

If light moved no faster than
a speeding bullet,

what would happen
to the world around us

if we slowed it down
by the same amount?

For example, a commercial jet

travels roughly 600 miles
an hour.

So assuming the bullet
represents the speed of light,

how slow would the jet look?

- At the scale
where the speed of light is

3,000 miles per hour,

then that commercial jet
is crawling along

so that it would take
an entire minute

to travel 3 inches.

Narrator: An F-15
can reach mach M.5.

That's over 1,500 miles
per hour.

But on this slow-light scale,

an F-15 needs a full minute
to move 7 inches.

And what about speeding bullets
themselves?

How slow do they look
on this slow-light scale?

[gunshot]

- If we go up to those
high-speed rifle bullets,

then they're making it just
a little bit more than a foot,

about 13 inches
over the course of one minute

at the scale
where the 3,000 miles per hour

is the actual speed of light.

Narrator:
In the real world,

a snail moves
more than twice as fast.

As it turns out,
much of the cosmos

is zipping around at speeds
we can't really comprehend.

- Motion is actually
the normal state of affairs

in the universe.

We may think
we're standing still—

And we are,
relative to the ground—

But Earth is orbiting the Sun,

the Sun is orbiting around
the center of our galaxy,

our galaxy is orbiting around
in our local group of galaxies.

Narrator: And all
of these objects are moving

at very high speeds.

- The Earth is orbiting the Sun

at a speed of about 66,000 miles
per hour.

That's enough to take you
around the Earth more than twice

in a single hour.

Narrator: Our Sun is rushing
around the Milky Way center

at 483,000 miles per hour.

And the Milky Way itself
is flying through space

at 1.3 million miles per hour.

But the speed of light is still
over 600 times faster.

The simple fact remains,

we live in slow motion

compared to the nature
of the cosmos.

Modern technology doesn't travel

anywhere near
the speed of light.

- If we travel, say,
at commercial-jet speed,

which is a million times slower
than the speed of light,

then it's going to take us
of order 4 million years

to traverse that distance
to the closest stars to the Sun.

Narrator: If it takes more years
to reach the nearest star

than the human race has existed,

how can any person
ever really understand

the size of our own galaxy?

By downsizing
the biggest planets and stars

and the velocity of light speed

to the level
of human experience,

we can finally begin
to understand

some of the scales
of outer space.

But is there a way
to do the same

for the distances
between the stars...

distances that utterly dwarf
the human imagination?

Although scientists measure
the enormous distance

between stars in light-years,

those numbers
barely help us grasp

the expansive nature
of the galactic landscape.

So let's shrink everything down
to a scale where one light-year

equals one mile.

On that scale,
our Sun shrinks down

to the size of a sand grain.

- We've calculated
just how many sand grains,

or how many stars,

would fill
our own Milky Way Galaxy.

And the number of stars
in the Milky Way

is about the same as the number
of sand grains in this chest.

Narrator: If you're counting,

that's more than
100 billion stars.

If one light-year
equals one mile,

where is the nearest star?

From the vantage point

of the Griffith Observatory
in Los Angeles,

where astronomer
Laura Danly works,

the nearest sand grain
would end up in Hollywood,

4 miles away.

To help pinpoint sand grains

positioned four miles apart
in a dense city,

we'll use mirrors
to flash sunlight

back and forth between them.

- So Aaron and Johnny
have mirrors,

and they're going to reflect
sunlight to help us see

just how far away it is
to the nearest star.

So I need to get a few stars to
take off to Hollywood with me.

That should do.

So, Stan, Aaron, are you ready?

You're going to be the Sun

staying here
at Griffith Observatory.

Johnny and I are headed out
to Hollywood.

You all set?

- Let's do it.

- All right, let's go.

Narrator: The nearest
celestial neighbor to our Sun

isn't a single star
but rather a grouping of three.

Two of them—
Alpha Centauri A and B—

Orbit each other

and are about the same size
as our Sun.

The third, Proxima Centauri,
is a red dwarf star,

dim and only about 10%
as massive as its siblings.

- I'm here on a rooftop
in Hollywood,

about four miles away
from Griffith Observatory

there in the background.

I have in my hand
a bag full of stars.

I'm going to take out
three sand grains—

One, two, three—

Throw the rest away—

That represent
our nearest stars.

Proxima Centauri is actually
the closest star to Earth.

And on the scale
of this analogy,

it's about 70 feet behind me,

so we'll just toss
Proxima Centauri

to its proper place.

Alpha Centauri A
and Alpha Centauri B

on this scale might be
about two feet apart,

while our Sun is four miles away
at Griffith Observatory.

Narrator: From here,

the sand grain
representing our Sun

will be impossible to spot.

This is where the mirrors
come in.

- Here we are at Alpha Centauri,

but now we have to find
our own Sun.

Let's see if we can't get them
to show us the Sun.

[cell phone rings]

- Hello, it's Stan.

- Hey, Stan,
we can't see the Sun.

You want to send us
a little sunlight our way?

- Okay, Sun's coming your way.

- Can't see it yet.

Uh, there.
That was a good one, yeah.

Nice and bright.

Wow, look at that.

That's incredible.

Okay, Stan,
we're going to show you

the light of Alpha Centauri now.

- Yes, yes.
There it is.

Yep, we saw it.

- They got it.
- Awesome.

- He sees Alpha Centauri.

Narrator: In our region
of the Milky Way Galaxy,

the typical distance
between stars

ranges from three to five
light-years.

With stars the size
of sand grains,

we could fit about 20 in a city
like Los Angeles.

But if more stars crowded
any closer to Earth,

our cosmic neighborhood
would become hazardous

to life as we know it.

[explosion rumbling]

- Supernova going off,

which would really cook
the atmosphere.

And if another star were to pass
too close to the Sun,

then the planetary orbits
would be badly perturbed.

Planets could even be lost
from the Sun

and sent out
into interstellar space.

It's really true that if we
didn't have these vast amounts

of real estate
between the stars,

we likely wouldn't even be here.

Narrator: Cutting down the
distance light travels in a year

helps put stars
in a clearer context.

But can we do the same
to grapple with

the practically infinite
dimensions

of the universe itself?

The Milky Way spans
100,000 light-years across.

And the next galaxy over is
really, really far away.

- The distance to the nearest
galaxy like our own—

The nearest spiral galaxy,
the Andromeda Galaxy—

Is about 2.5 million
light-years away.

That's about almost 25 times

the size
of the Milky Way itself.

So if you lined up
25 Milky Ways end on end,

that would stretch
to the Andromeda Galaxy.

Narrator: It might be clearer
to scale things down some more

and imagine galaxies
as urban centers

spread out
across the United States.

- Sometimes galaxies are
referred to as star cities,

and that's
a pretty good analogy.

Narrator: If we envision
the Milky Way Galaxy

at the size of the Los Angeles
metropolitan area,

roughly 100 miles wide,

then Andromeda would be
in New York.

In between
would be other members

of what astronomers call
the "local group” of galaxies.

- There's basically two major
players in the local group.

There's our galaxy—
the Milky Way Galaxy—

And there's
the Andromeda Galaxy.

There's another smaller
spiral galaxy knows as M33.

And then we also have
these dwarf galaxies,

which contain 100 million stars,
sometimes even fewer.

Narrator:
But even the vast distances

that separate members
of the local group

won't be enough to save
our home galaxy.

- Andromeda and M33 are both
headed toward the Milky Way,

to the point where,
in a few billion years from now,

they're going to have
a close encounter.

Narrator: On a cosmic scale,
the collision seems violent.

But in fact,
the stars in the galaxies

are so widely spaced,

they will weave past each other,
largely undisturbed.

If humans survive that long,

they'll hardly notice it
here on Earth.

- And a few billion years
after that,

they'll have merged
into a single galaxy.

Narrator. The Milky Way
as we know it

will cease to exist.

Until that time comes, though,

the distances between
even the nearest galaxies

of the local group
remain beyond our grasp.

And our galactic neighbors
represent only a small sliver

of our immense cosmos.

- In the observable part
of the universe,

there's something like
100 billion galaxies,

each with billions of stars.

Narrator: If galaxies
were spaced out

like urban centers
throughout the United States,

then to approximate the size
of the observable universe,

the country
would have to be large enough

to wrap around the Earth
about 500 times.

Shrinking the universe
down to human scale

may help us comprehend its size,

but reality, of course,
doesn't work that way.

- The vastness of the universe

sometimes makes us feel
really small.

We're small compared
to the solar system,

small compared to our galaxy,

compared to the universe
as a whole.

But in some ways, I think
we're not insignificant,

because we're the only creatures
we know of

that have the advanced minds
and curiosity and intellect

to think about the universe.

In a sense, we are the way
in which the universe has found

to know itself.

Narrator: And so that must mean

the universe is finally starting
to figure out

how awe-inspiringly vast
it truly is.