All language subtitles for How.the.Universe.Works.S10E01.Secrets.of.the.Cosmic.Web.1080p.WEB.h264-KOMPOST.ENG

ROWE: The night sky.

Countless stars
and the majestic sweep

of the Milky Way, but beyond
our local neighborhood,

across the cosmos,
there are over

two trillion more galaxies.

THALLER: When we first began
to observe galaxies,

we collected them
like butterflies.

Little by little,
we realized that

they formed a web.

ROWE: The cosmic web is
the infrastructure that connects

every corner of the universe.

You don't know anything
about our universe

if you don't understand
the cosmic web.

It feeds galaxies.
It forms galaxies.

It is made of galaxies.

ROWE: It's the architect
of everything,

and our cosmic future
depends on it.

The cosmic web is one of
the most important parts

of our universe --
It plays a key role

in the evolution of the cosmos.

Without the cosmic web,
there would be no stars,

no planets, nowhere in
the universe where

the conditions of life
could exist.

ROWE: How did the universe go
from a hot soup of gas

to a cosmic web,
sprinkled with galaxies,

planets, and us?

The universe may appear random.

Two trillion galaxies,
spread across the cosmos.

But in this cosmic chaos,

scientists detect water.

When we first saw that
the universe was full

of galaxies, it seemed like
overwhelming chaos,

but it's not --
They're all connected.

ROWE: Galaxies link up
in a gigantic cosmic network

spanning the entire universe.

How this pattern emerged
may be cosmology's

biggest puzzle.

In some senses, you don't
understand something

unless you understand
how it comes into existence

and how it's formed.

And galaxies are the basic
building block

of our universe.

ROWE: To solve this mystery,
scientists need to go deep,

to the very edge of
the observable universe,

and study light from
the first galaxies.

Chile, 2021.

Scientists point the VLT,
or Very Large Telescope,

towards the Hubble
Ultra Deep Field.

It's a patch of sky
famously photographed

by the Hubble Space Telescope
in 1995.

The VLT's power allows
astronomers to see

much deeper into space.

Imagine you take
a grain of sand,

and you put it
on your fingertip,

and you hold your arm out
like this,

and you block a part of
the sky looking

at that grain of sand --
That's the size

of the Hubble Ultra Deep Field,
and yet it contains

thousands of galaxies in it.

ROWE: The telescope stares
at those galaxies

for 155 hours and picks up
the faintest of glows...

ancient hydrogen gas
concentrated along a strand

of space 15 million
lightyears long.

The filaments are just
one tiny section

of the cosmic web,
the largest known

structure in the universe.

The scale of the cosmic web
is enormous.

It is, by definition,
the largest thing

that we can see in our universe.

ROWE: Today, the cosmic web
is a lattice of filaments,

linked streams of hydrogen gas

that form an intergalactic
network spanning

the entire universe.

Inside the nodes of
the cosmic web,

you'll find galaxies
and stars and black holes.

Along the filaments,
you'll find gas

that connects these nodes,
and the gas will connect

to the other galaxies
and clusters of galaxies.

It's this beautiful
superhighway of

large cities that are connected
through these filaments.

BULLOCK:
We can see the cosmic web

about as far back as
we can look,

and really, galaxies are
forming along that web

all the way back.

ROWE: This cosmic
infrastructure dates back

to the earliest days
of the universe.

13.8 billion years ago,

the universe ignites in
a tiny ball

of super hot energy.

It expands and begins to cool.

Energy transforms
into primitive,

subatomic particles of matter.

The heat from the Big Bang
is so intense,

gravity is
effectively powerless.

The very early universe was
super hot,

super energetic,
and regular particles

of matter were zipping around
so fast

that not even gravity
could hold them together.

But regular matter wasn't
the only thing

in the early universe.

ROWE: In the background,
gravity is working

on something else --

Regular matter's ghostly cousin,

the invisible substance
known today as dark matter.

It makes up about 85 percent
of all the matter

created in the early universe.

Normal matter and dark matter
both existed

around the time of the Big Bang,
but they way they played out

was very different.

ROWE: Just ten seconds after
the Big Bang,

the infant universe is
billions of degrees Fahrenheit,

still far too hot for
regular matter particles

to clump together, but dark
matter plays by different rules.

Dark matter isn't affected by
the Big Bang's intense

radiation in the same way
that regular matter is,

and so because it's able
to cool,

it clumps together in a way
that regular matter doesn't.

ROWE: As dark matter clumps
grow, they exert

a gravitational pull and begin
to form shadowy structures.

As soon as the dark matter
gets a foothold,

we have a place where there's
a bit more stuff,

then that attracts
more and more dark matter.

ROWE: 380,000 years after
the Big Bang,

the intense heat drops
to a few thousand degrees.

Normal particles of matter
move around more slowly.

Protons and electrons bind
together and form

atoms of hydrogen
and helium gas.

Then gravity from dark matter
starts to work

on regular matter.

Before you know it,
you have this very clumpy

universe with these huge
dark matter halos

that can now start to draw in
also ordinary matter

in the form of gas.

ROWE: A billion-year building
project begins.

The dark matter clumps
pulled in clouds of gas...

the foundations of
the cosmic web and the galaxies.

Just as when you build
a building, you know,

there's a lot of work that
happens before

the building goes up,
our universe spent

a lot of time laying
the groundwork for

this cosmic web before
it switched on the lights.

ROWE: The foundations
are complete,

but the job isn't finished.

How did those clouds of gas
transform into the greatest

structure in the universe?

The secretive dark matter
that brought the gas together

is also on site,
managing the build.

It was really the dark matter
that called the shots

in cosmic clustering,
because it outweighed

the ordinary stuff by
a big factor.

In essence, the cosmic web
is made of dark matter.

Tendrils of material are
stretched out across the cosmos.

ROWE: As the sprawling structure
builds, its gravitational

pull strengthens, pulling in
more dark matter.

The clumps begin to collapse
and shrink down

into filaments -- these meet
at even more tightly

packed clusters, creating
a huge, dark scaffold

that drags in more hydrogen gas.

BULLOCK: Imagine drops of dew
on a spider web.

That's like hydrogen blobs
being pulled in

to dark matter's cosmic web.

ROWE: After tens of millions
of years of construction,

strands of gas stretch
across the cosmos.

Fast forward to now --
The web appears

in all its star-spangled glory,
lit up with galaxies.

We know at some point,
stars and galaxies formed.

The big question is when --
What were the first

galaxies like?
That's a big mystery.

ROWE: So how then did the lights
of the cosmos switch on?

Evidence suggests that as
the universe assembled its web

of dark matter and hydrogen gas,

the biggest stars that have
ever lived

set the cosmos ablaze.

ROWE: 2018, scientists study
an ancient galaxy,

the catchily named MACS1149-JD1.

There, they find some of
the oldest stars

ever detected.

This particular galaxy is
exciting, because it's

forming stars just a very
short time after the Big Bang.

ROWE: Those stars could hold
clues as to how

the cosmic web that supports
the universe

first lit up,
but as astronomers study

starlight from when
the universe was just

250 million years old,
they get a shock.

The stars are not just
made up of hydrogen

and helium produced
in the Big Bang.

They also contain what
astronomers call metals.

Metals in astronomy is
everything heavier

than hydrogen and helium.

SUTTER: No matter where it is
on the periodic table,

if you're not hydrogen
or helium, you are a metal,

even though that makes no sense.

If I were king of astronomy,
metals is right out.

NANCE: The Big Bang only
made hydrogen and helium.

Anything heavier than that
was churned up in

the cores of dying stars.

ROWE: The bright stars of
this ancient galaxy

dating back to just 250
million years after

the Big Bang contain chemicals
that were created

in even earlier stars.

Some of them seem to be
nearly the age of

the universe, extremely old,
and yet they contain

elements that guarantee
they can't have been

the first generation --
As old as these stars are,

there must have been something
that came before.

ROWE: The earlier first
generation of stars

remains cloaked in mystery.

How did the first stars ignite,

and did they kickstart
the formation

of the first galaxies?

It sounds like a classic
creation myth,

it's out of the darkness,
out of nothing,

structure arrived,
and from that structure,

the galaxies, the lights
in the universe, turned on.

ROWE: We've never seen
a first-generation star,

but physicists have a theory
of how they formed

and what they were like.

Let's step even further
back in time,

to around 100 million years
after the Big Bang.

The early cosmic web is dark.

There are no stars
to illuminate it.

But the universe is ready
for stellar ignition.

Cooled down after millions
of years of expansion,

the gas clouds clinging
to the dark matter scaffold

begin to contract.

As the hydrogen gas
clumps together,

larger clouds form super dense,

ultra hot cores.

THALLER: If you can bring
hydrogen together,

and actually get it hot
and dense enough,

hydrogen will begin to fuse
into helium.

There will be a nuclear fusion
reaction going on.

ROWE: Simulations suggest that
some gas clouds are

hundreds of times the mass
of the sun.

The stars they produce

are unlike anything
that exist today.

So the stars around us today
really top out at masses

between let's say 70 to 100
times the mass of our sun.

There's nothing larger
than that.

NANCE: These first stars
were up to 1,000 times

more massive than the sun,
so if you plopped it

in our solar system,
it would extend

all the way past Jupiter --
So think about that.

That is incredibly big.

That scale is mind-blowing.

ROWE: So what happened to
these stellar behemoths?

THALLER: The lifetime of a star
has a lot to do with its mass.

The more massive a star is,
the more gravity crushes

the interior up to high
temperatures, and it burns

through its nuclear fuel
even faster, so incredibly,

the more mass there is,
the shorter a lifetime

you get for a star.

OLUSEYI: The first generation
of stars are sort of like

the rappers and rock stars of
the universe.

They live fast, they die young.

ROWE: First generation stars
didn't live long enough

to form complex galaxies,
but they did set

the process in motion.

The lives of the first stars
may have been rock and roll,

but their explosive deaths
and supernovas

pump the universe full
of heavy metal.

THALLER: In the galaxy today,
we see a supernova

maybe every couple of years,
close to us every

couple of decades -- this must
have been a fireworks show,

giant supernovas going off
all the time, all around you.

OLUSEYI: That act of destruction
is actually an act of creation.

What a star does in its core
is it creates

heavier elements
from lighter elements.

THALLER: That first generation
of stars must have been

absolutely incredible,
simply exploding

so quickly and unloading all of
this wonderful new chemistry

into the galaxy.

ROWE: 200 million years after
the Big Bang,

the remains of the first stars
flood the interstellar medium

with heavier elements,
like carbon, oxygen,

silicon, and iron,

crucial ingredients for
the next wave of stars.

It's such a beautiful story,
because suddenly the whole

process of star
formation changed,

and it literally became easier
to make a star.

ROWE: Heavy elements suck heat
out of the surrounding gas.

Cooler clouds crunch down
must faster.

The smaller, second-generation
stars form rapidly

and in much greater numbers.

Somehow, this mess of stars
transformed into a network

of young galaxies,
but it wasn't easy,

because as these
baby galaxies formed,

a breed of
matter-hungry monsters

appeared in
the young cosmic web.

ROWE: 13.6 billion years ago,
the dark scaffold

that supports all the regular
matter in the universe

emerges, ablaze with stars.

But how did this stellar
array evolve into a structure

littered with
organized galaxies?

It seems they formed under
constant threat of destruction.

October 2020.

Astronomers discover
a monster lurking

among the cosmic web's
earliest structures,

dating to 900 million years
after the Big Bang,

a supermassive black hole.

Six galaxies surround
this cosmic giant,

caught in its grip,
seemingly linked to

the supermassive black hole
by filaments

of the developing cosmic web.

It's like the universe has
given supermassive black holes

an umbilical cord.

It's like an all-you-can-eat
buffet, right there.

ROWE: Supermassive black holes
are hungry beasts.

They feast on any matter
that gets too close to them.

MINGARELLI: Supermassive black
holes are likely some of

the most powerful objects
in the universe.

They can be anywhere between
100,000 to 10 billion

times the mass of the sun.

ROWE: Supermassive black holes
have been a nemesis

for generations of scientists,
not because of

their fearsome nature,
but because nobody knows

how they grew so large,
so early.

SUTTER: I wish I knew where
supermassive black holes

came from -- if I knew,
I would have a Nobel Prize

hanging around my neck,
and I would wear it

every single day.

As someone who deeply
loves supermassive black holes,

whose career is based on
studying supermassive

black holes, it is very
frustrating to not

know where they come from.

ROWE: Regular stellar
black holes are the collapsed

cores of dead stars,
ranging from

three to thousands of
solar masses,

but supermassive black holes,
those are a different beast.

Thirteen billion years ago,
not enough stars

had lived and died to build
something as huge

as a supermassive black hole.

Now, the cosmic web offers
scientists clues

about the black hole conundrum.

We now know supermassive
black holes grow

among the lattice of
the young cosmic web,

gorging on the hydrogen gas that
travels along the filaments.

At the same time,
when the cosmic web

is lighting up,
supermassive black holes

appear to be stealing star fuel
from the young universe.

You might think that would
kill a growing galaxy,

and yet most mature galaxies
have a supermassive black hole.

They really dominate
the physics of what happens

in the centers of galaxies,
and even how galaxies

can evolve.

ROWE: We think these galactic
monsters have been around

from the start --
How then did the web's

young galaxies develop around
supermassive black holes?

The Milky Way's supermassive
black hole is called

Sagittarius A-Star.

It's around 27 million miles
wide and weighs in

at just over 4 million
solar masses.

MINGARELLI: The environment
around Sagittarius A-Star

is very dynamic --
It can actually be

a really hellish place --
There's this accretion disk

that's full of plasma,
it's heated to

thousands of degrees,
so you wouldn't necessarily

think that that's a great
place for star formation

to happen.

ROWE: But that's exactly
where astronomers

decided to look.

Using the Atacama Large
Millimeter Array,

or ALMA for short,
scientists scan

the heart of the Milky Way
for dense cores of gas and dust,

stellar embryos.

They found more than 800 within
just a thousand lightyears

of Sagittarius A-Star,

including more than 40 embryos
with energetic jets

blasting from their cores,
the telltale sign

of the birth of stars.

MINGARELLI: It's really
surprising to find

those stars there --
It's like hearing

babies' cries from a wolf's den.

PLAIT: It's not the place
you would expect this to happen,

but in fact, stars are
forming there.

Now, it's not as efficient
as it is out here

in the suburbs where things are
quieter, but it works.

ROWE: Baby stars igniting
and thriving around

a supermassive black hole,
the kind of

hostile environment we know
existed in the young

cosmic web --
Star birth is a key part

of kickstarting young galaxies.

This evidence suggests
that star formation

is more resilient
than researchers thought,

and they've developed a theory
to explain it.

Gas and dust race around
the black hole

in the accretion disk --
Heated to incredible

temperatures, plumes of gas
break off

and blast into space.

The gas rapidly cools,
collapses,

and forms baby stars --
These accretion disks

are the most chaotic of
stellar nurseries.

You see this mechanism that
you think is violently

inhibiting star formation,
and at the same time,

it's triggering the birth
of new stars.

ROWE: Matter clumps at
the cosmic web's intersections,

feeding the supermassive
black holes.

Around them,
stars burst into life,

slowly building galaxies.

This could be how our own
Milky Way formed

among the filaments
of the young cosmic web.

But new research suggests that
growth in these baby galaxies

requires murder and mayhem,
and without them,

we wouldn't exist.

ROWE: The infant universe
is a dramatic place.

Stars ignite, and stars die,

even in the violent surroundings
of supermassive black holes.

Baby galaxies form
with the cosmic web.

But how do they grow?

Scientists believe the critical
factor is galactic turmoil.

The universe does need
to churn things up.

You need to break some eggs
to make an omelet.

You need to introduce some
chaos into your galaxy

to rapidly form stars
or grow black holes.

Smashing things together
is how the universe came to be.

ROWE: The Hubble Space Telescope
discovers many distorted

galaxies -- twisted,
battered, and torn,

victims of violent collisions
on a cosmic scale.

HOPKINS: Galaxies are never
sitting quietly, doing nothing.

They're always undergoing
change -- they're constantly

encountering and slamming
into and colliding with

and mixing with other galaxies.

MINGARELLI:
You can see images in Hubble

of total car wrecks,
of galaxies that are

trying to merge with each other.

ROWE: We know that galaxies
collide now,

but what about
in the early universe,

when the cosmic web was
beginning to take shape?

Astronomers study a strange
galaxy named Himiko,

born just 800 million years
after the Big Bang.

Three bright light sources
suggest intense star formation.

Detailed analysis reveals
not one galaxy,

but three baby galaxies,
not yet fully formed.

Scientists call these youthful
star systems protogalaxies.

The trio that make up
Himiko are in mid-collision.

Computer simulations of
the early universe suggest

protogalaxies smashed together
with frightening regularity.

These violent shake-ups
trigger star birth.

Protogalaxies are rich in gas,

and when they collide and merge,
those gas clouds

collide and collapse
and form stars,

sometimes, at prodigious rates,
and after a billion years

or so, all of that structure
forms, and you get

a formal galaxy.

ROWE:
Picture the early universe,

500 million years after
the Big Bang.

It's smaller and more compact
than today.

Cosmic collisions are common.

PLAIT: Imagine taking a bunch
of cars and just letting them

drive around in Nevada where

there's nothing but space,
right?

You're not gonna get
too many collisions.

Now squeeze them into
a tiny little city block

some place, and you're just
gonna have accidents everywhere.

Well, it's the same thing
with the universe.

When the universe was younger,
it was smaller,

and these protogalaxies
were everywhere.

It was crowded.

You were bound to get collisions
between them back then.

ROWE: More and more baby
galaxies form at the growing

web's gas-rich intersections.

A collision between small
protogalaxies

might trigger modest amounts
of star formation

when regions of dense matter
come together.

But a merger involving

protogalaxies with rich
reserves of gas

can rev up the rate of
stellar ignition,

supercharging a growing galaxy.

Gas-rich mergers can
generate starburst galaxies,

where we see incredibly vigorous
events of star formation.

ROWE: Astronomers think
one such smash-up,

around 10 billion years ago,
kickstarted the growth

of the Milky Way.

A group of stars called
the Gaia Enceladus Cluster

in the outer reaches of
the galaxy

behaves strangely compared
to other stars around it.

SUTTER: The stars
in the Gaia Enceladus Cluster,

they're different,
they move differently,

they act different,
they're like -- they're like

kids from the next town over
showing up at your school.

You just know
that they don't belong.

The Milky Way had already
largely formed,

and then this massive cluster
comes screaming in.

It was a violent event

that eventually ended up
absorbing the stars

from this cluster
into the body of

the Milky Way itself.

Galaxies are built from
these kinds of collisions.

ROWE: Less than a billion years
after the Big Bang,

the dark scaffold of the cosmic
web begins to glow.

Matter channeled down the web's
tendrils creates

dense clumps of gas --
Even in the turbulent

neighborhoods of supermassive
black holes,

stars burst into life.

Baby galaxies collide,
and the young universe

sparkles with light.

But an important
question remains.

In the mayhem of
the early universe,

how did galaxies
like our Milky Way

survive and thrive?

MINGARELLI: Galaxy evolution
is very dynamic.

Our understanding of galaxy
evolution is very dynamic,

and there's so much that
we still don't know.

There's a lot of different
competing theories

right now as to how galaxies
grew into the galaxies

that we see today.

It's a huge open question,
and it's something that's

a big deal in science right now.

ROWE: New research suggests
that life and death

in the cradle of the universe
lay within

the cosmic web.

ROWE: 13.6 billion years ago,

a protogalaxy,
the infant Milky Way,

forms in the tendrils of
the young cosmic web.

Today, it bears the scars

of many collisions.

Each one could have
torn it apart.

So what controls if a young
galaxy lives or dies?

May 2020.

Scientists image a graceful
galaxy that existed

just 1.4 billion years
after the Big Bang.

Analysis of its light shows this

is a starburst galaxy,
pumping out newborn stars.

Galaxies like our Milky Way
are old and rather stately,

and they don't form stars
very rapidly --

About the equivalent of the mass
of the sun every year.

Well, starburst galaxies --
Yeah, they form them

a lot more quickly -- hundreds
of solar masses per year.

But BRI 1335-0417,

4,650 times the mass of
the sun every year.

It is blasting out stars.

ROWE: Some young galaxies
in the early universe

appear to be supercharged
with star fuel.

How can they grow at such
an incredible pace?

Scientists think the answer
lies in the mysterious substance

that's controlled the flow
of gas since the beginning --

The dark structure
whose tendrils stitch

the universe together,

but exploring this cosmic
network is no easy task.

When it comes to dark matter,

we're flying blind.

May 2021.

An international team of
researchers investigates

dark matter in the local
universe by observing

its effect on the path of light.

Gravity affects light.

A massive object causes light
to curve

through space, even if
that object is invisible,

like dark matter.

We can't see the dark matter
directly, but we can see

what it's doing to the light --
It's stretching it,

it's bending it,
it's creating arcs in ways

that would never happen unless
the dark matter were there.

ROWE: Using an AI program,

the team analyzes 100 million
visible galaxies,

looking for
warped galactic light.

Because the model is
artificially intelligent,

it gets better and better
at finding dark matter.

What's very clever
about this kind of algorithm

is that it's learning
as it goes.

It uses the information
that it has

to predict the existence
of new structures.

ROWE: As the model teaches
itself to see

the dark matter behind
the stars,

it maps out new,
dark structures,

never-before-seen highways
between galaxies.

There's a lot more filaments,
there's a lot more

intricacies, there's a lot
more cosmic web there

than what meets the eye.

It's like if you look how

Manhattan is connected
to the land around it,

you can see all the bridges,
but now we're also seeing

the underwater tunnels.

ROWE: The new layout
of dark matter reveals

the local universe is a bird's
nest of hidden channels,

feeding galaxies with gas.

Galactic structures seem
to thrive

at the cosmic web's most
densely-knotted intersections.

Because multiple filaments
are intersected

in those locations,
and that is a location

of very enhanced gravity
relative to other locations,

the material will be drawn in,

so these galaxy clusters are
likely feeding off

the cosmic web.

ROWE: This connectivity could be
the key to the rapidly-forming

galaxies in the early universe,
but there's a catch.

Sitting right at the densest
regions of

the cosmic web can be really
good for galaxy growth.

You have all of this gas
being funneled in

for a new star formation,
but being that plugged in

to the network isn't
all good news.

ROWE: There is evidence that,
though the cosmic web

gives life, it can also
take life away.

Scientists studying some of
the universe's most heavily

connected galaxies
found something unexpected --

Plummeting rates of star birth.

In some ways, it's a little bit
counter-intuitive, right?

If these nodes are meeting
grounds for all of

this gas, right, why aren't
you forming more stars there?

ROWE: One explanation?
In the all-you-can-eat buffet

of the cosmic web's
matter-rich junctions,

a young galaxy might
over-indulge.

As the cosmic web funnels
more matter towards a junction

and its growing galaxies,
the gas influx doesn't

just boost star formation,
it fattens up

the supermassive black hole
at the galaxy's core.

For a young galaxy,
that's dangerous,

because when this monster
over-eats, it produces

high-energy jets and belches out

super hot wind.

These black holes radiate
tremendous amounts of energy

when they grow,
and that radiation can

slam into the material
around them in the galaxy

and blow it all out of
the galaxy, launch it away

or heat it up to
super high temperatures.

Star formation requires stuff,
so if you blow that stuff

away, how are you gonna
form a star?

And what's left behind
would be what we call

a quenched galaxy that basically
can't form any new stars.

ROWE: The researchers found
that although connectivity

within the cosmic web can boost
galactic growth,

it was the super connected
galaxies that died

the quickest, choked and stunted
like over-watered plants.

Perhaps our Milky Way got lucky.

You could say that
the Milky Way Galaxy is sort of

in this Goldilocks zone
of galaxy formation.

It's been receiving enough
gas over time that it's

been able to keep up with
its star formation

but not so much gas that
its central black hole

has been fed enough that
it would clear the galaxy

out of gas.

ROWE: The cosmic web determined
if galaxies lived or died.

Its construction project
brought order to chaos.

The cosmic web is
the architect, the engineer,

the builder, the construction
worker, even the interior

designer of the cosmos.

ROWE: But now,
work has shut down.

An invisible force threatens
to tear apart the very

fabric of the cosmic web --
What does this mean

for galaxies and for us?

ROWE: The cosmic web brought
order to the early universe.

The gravitational attraction
of its dark scaffolding

helped build galaxies
and fueled their development.

But growth tops out at
the level of galaxy clusters.

Nothing bigger will ever form.

Something has stopped
the formation of structure

in our universe.

ROWE: To understand
what's going on,

we need to return to
the Big Bang

and the formation of
the cosmic web.

13.8 billion years ago,
the universe sparks into life.

A tiny ball of pure energy
cools and expands.

The energy transforms into
regular matter

and dark matter,
but another force appears

at the same time -- dark energy.

Dark energy,
as far as we understand it,

which is not much,
has always been here.

It's always been a part of
the universe,

but it's been silent,
in the background.

Dark energy is everywhere --
It's over here,

it's over there,
it's between you and me.

It's absolutely everywhere.

One theory is that dark energy
never formed,

that it's just a constant
in the laws of physics

that has always been there
and always will be.

ROWE: Some physicists believe
that dark energy

is simply the force
of emptiness.

TEGMARK: People used to take for
granted that space was empty,

a vacuum, but the discovery
of dark energy

has made some people wonder
if space is actually

more of a substance,
and, um, that space also

might have pressure that
causes things

to push apart, so, you know,
whatever space is,

it might be more interesting
than we thought.

ROWE: Dark matter
dominates the young universe,

but as the dark scaffold
of the cosmic web grows,

it sows the seeds of
self-destruction.

As the network of matter
takes shape,

pockets of emptiness form
between the filaments --

Cosmic voids.

In these expanding hollow
spaces, dark energy grows.

The weirdest thing about
dark energy is that

it has constant density --
Constant density means

the more volume you have,
the more dark energy you have,

so the larger the voids get,

the more dark energy
they contain.

ROWE: Dark energy pushes
against the cosmic web,

opening up huge chasms in

the architecture
of the universe.

Five billion years ago,
dark matter's strength of

attraction is finally
overwhelmed.

Like bridge cables
in a hurricane,

the cosmic web's filaments
stretch and snap,

and the universe's substructure
fails.

Galactic construction freezes
as the universe expands,

but darker times are ahead
for the cosmic web.

As time goes on,
not only is it expanding,

but this expansion gets faster
and faster and faster.

ROWE: As the dark energy
in the voids increases,

the entire structure of
the cosmic web

begins to break up.

The effects of dark energy
will get stronger

and stronger with time,
until the very fabric

of space time gets torn apart.

This isn't a superhero movie --
The bad guy wins.

The future of the cosmic web
is looking bleak.

Ultimately, it's gonna be

a cold, lonely universe.

ROWE: Our closest galaxies
will accelerate away,

until they're just tiny
pinpricks of light.

Then the universe
will go dark again.

Everything will fade out.

So the universe started
with a bang,

but it will die with a whisper.

ROWE: The cosmic web
transformed the universe

from a hot mess
to a sparkling structure.

It gave birth to billions
of galaxies and us.

Without it, space would be

a much less interesting place.

This giant structure, the
largest thing that we know of

in the universe, is responsible
for nourishing the galaxies,

creating the stars,
making the conditions right

to form life -- we would not
be here, talking right now,

if it were not for
this cosmic web.

SUTTER: Understanding
the cosmic web

is understanding dark matter,
is understanding dark energy,

is understanding our past,
is understanding our future.

Really, everything that we know
about how the universe works

is directly tied
to the cosmic web.

It's amazing to think that
the overall structure of

the universe that we witness
today began in the earliest

times of the universe
and has yielded

beings like ourselves
who can now

discover it and ponder
about its existence.

That's pretty dope.