Space's Deepest Secrets (2016–…): Season 8, Episode 2 - Space's Great Wall - full transcript

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In 2016,

astronomers make an
extraordinary discovery

out in deep space.

A cosmic megastructure,

one billion light-years long...

The great wall.

You could put 10,000
of our galaxies end to end,

and that's how big
the great wall is.

Investigators are now
racing to decode what shapes

the most massive and mysterious
structure in the universe.

Something,
some force or process,



caused the great wall

to be sculpted in this
really particular way.

Can an
alien-like creature reveal

how the great wall
fits into the cosmos?

This may be our best model
of how the cosmic web was built

and what strange force
will define its future?

It, too, shall pass.
It's not going to last forever.

To find out,

we dive into
the great wall's fiery birth

and hunt for the weird cosmic
glue that holds it together

to reveal how this megastructure

rewrites our understanding
of the universe

on an epic scale.

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our observable universe is vast.

Astronomers estimate
that it measures

93 billion light-years across

and that it contains hundreds
of billions of galaxies.

From earth,
it looks like these galaxies

are entirely separate
from one another,

solitary islands adrift
in the expanse of space.

Almost all of
the universe is empty.

It's just cold and dark.

We have telescopes that are
looking farther and farther out,

and there seems to be
just more and more space

between the galaxies,
more darkness.

But astronomers today
are finding patterns

among the stars.

This evidence shows
that many galaxies

share a mysterious connection.

In January 2016,
astronomers spot something huge.

830 visible galaxies,

trillions of stars,

woven into what appears to be
a single, flattened structure

one billion light-years tall
and almost as wide.

This wall of galaxies

is the most massive structure
in the universe.

Astronomers name it after

the baryon oscillation
spectroscopic survey

that makes the discovery...

The boss great wall.

What is this strange,
giant structure?

The special telescope
that finds the great wall

has a unique way
to hunt for clues.

This is the
Sloan digital sky survey,

or SDSS for short.

SDSS works differently
to a regular telescope.

Instead of astronomers saying,

"hey, I'm interested in that
object right there in the sky"

and pointing a telescope there
and looking at it,

the Sloan digital sky survey
tiles the sky.

It's sort of squat and wide,
and it has a wide field of view.

So it sees a lot more of the sky
in one image

than a typical telescope.

So you can create one big
super image of the sky from it.

A quirk of physics
allows this telescope

to draw a special
color-coded map

that plots the positions
of objects in the universe

with pinpoint accuracy.

This is how it works.

As our universe expands,

it stretches the fabric of space

and forces objects
further and further apart.

This stretches the light
that these objects emit

and shifts its
wavelength and color

to the red end of the spectrum.

The further away an object
is from our telescopes,

the stronger this redshift
will be.

SDSS can measure this redshift
of distant galaxies

to map the cosmos
in three dimensions.

The SDSS data reveals
that the great wall

is a clearly defined
physical structure.

It is deep as well as long.

The body of the great wall
consists of

the densest concentration
of galaxies ever recorded.

And this makes it
the most massive structure

in the universe
that astronomers have ever seen.

Why is it here?

How did it form?

Astronomers believe the answer
lies in the key building blocks

of the great wall...

Its trillions of stars.

A star is a giant
nuclear reactor

that fuses atoms of hydrogen
to produce light and heat.

From one end of
the universe to the other,

all the light we see
out there is produced

by the same simple thing...
Nuclear fusion.

And that's true close by
with our sun

and in the most distant reaches
of the universe.

It's our beacon in the darkness.

It takes a vast amount
of collapsing gas

to make the huge number of stars
in the great wall.

The great wall is not only

the most massive structure
ever seen.

It is also the greatest
concentration of hydrogen

yet found in the universe.

The mass of the great wall is

almost unbelievable.

If our galaxy...
Our massive, giant galaxy...

Were, say, the mass of
a stick of butter,

the great wall
would be the mass of a car.

The great wall owes its Genesis

to a super huge cloud

made mostly of hydrogen
that clumps together

in one part of space.

How does so much gas end up

dumped in this region
of the universe?

A clue lies in the data
that special satellites

like NASA's WMAP probe
beam back to earth.

The data draws
this extraordinary image.

It is a picture of the universe
when it is

just 380,000 years old.

It shows the spread
and concentration

of ancient microwave energy.

Astronomers call this
the cosmic microwave background,

or CMB.

The cosmic microwave background

is literally what it says.

It is a background glow
of the universe

in the wavelengths
of microwaves.

What it really is, is sort of
the cooling off of the fireball

of the big bang itself.

It is a snapshot of the universe

when it was only a few
hundred thousand years old.

The CMB captures the
moment after the big bang

when the universe cools

just enough for
the first atoms of gas to form.

The image shows that the
concentrations of this matter

in the early universe varies
from place to place.

Astronomers believe that the
patches of the early universe

with the highest concentrations
of gas eventually evolve

into structures
like the great wall.

But what triggers this
unevenness in the first place?

And what is the
mysterious ingredient

that glues
the great wall together?

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The boss great wall

is the largest cosmic structure
ever discovered.

It owes its origin
to a super huge cloud of gas

that collects
in the early universe.

But why does this material
clump together here

in the first place?

Astronomers believe that
the answer lies at the moment

of the universe's creation,

at a time when everything
in existence

fits into a space
far smaller than an atom.

The tiniest sliver
of a fraction of a second

after the big bang,

110 trillion, trillion,
trillionth of a second,

the universe underwent
an inflationary period

where it went from about
the size of a proton,

a subatomic particle, to roughly
the size of a grain of sand.

Now, I know that
doesn't sound like much,

but you've got to realize
this is a factor of a million,

billion, billion times.

This is a huge expansion.

This moment of inflation

sows the seed that grows
into the great wall.

Trillionths of a second
after the big bang,

the cosmos is a ball of energy
where weirdness rules.

Minute random fluctuations
in this super hot soup

create a pattern of hot spots
on subatomic scales.

As the universe expands,

it stretches out the tiny
hot spots over a cosmic scale.

Energy condenses into matter,
which provides the seeds

for huge cosmic structures
like the clouds of hydrogen

that feed the galaxies
in the great wall.

The inflation of the universe

pulled parts of the universe
that were close together

wildly apart.

If you had a region
of the universe

that had a little bit
more stuff in it than average

next to a spot that had a little
bit less stuff than average,

given enough time, they would
have smoothed each other out.

But the inflation of the
universe ripped them apart,

and they became frozen in place.

Tiny fluctuations

at the moment
of the universe's creation

unlock the Genesis of the
largest structure in the cosmos.

What is the invisible force
that molds trillions of stars

into the great wall's
distinctive shape?

The great wall is 6 billion
light-years from earth.

This is too far away
for telescopes

to see in detail
how it joins together.

But clues exist closer to home

that can help astronomers
unlock the mystery.

Despite its ridiculous
size and forbidding distance,

the great wall is made of the
same things we see around us.

We can learn about that and then
extrapolate that to understand

how the great wall
itself behaves.

Our milky way galaxy
is just one of a cluster of over

30 closely spaced galaxies
known as the local group.

And the local group
is just a single fragment

of an even greater collection
of hundreds of galaxy clusters.

Astronomers call this type
of structure a supercluster.

The milky way
is part of a supercluster

that is 100 million
light-years wide.

And superclusters
pop up everywhere

that astronomers look.

Almost every galaxy
is part of a supercluster,

and there are millions of these
superclusters in the universe.

Each one of them has tens
to hundreds of thousands

of galaxies in them.

And each one of those galaxies
has billions of stars.

The supercluster is the key

that unlocks why the great wall
has its distinctive shape.

The great wall measures
one billion light-years across.

Breaking it apart reveals

that it is a cluster
of four superclusters.

Two of them are large,
densely packed tubes,

each more than 500 million
light-years long.

And two are smaller
superclusters,

each over 1,000 times
the mass of the milky way.

These superclusters
joined together

to form a true heavyweight
champion of the cosmos,

the largest single object
we have ever seen.

Astronomers now know
that 9 out of 10 galaxies

sit inside a supercluster.

What mysterious force
brings galaxies together

into these vast structures?

A clue lies in the way

that everything moves
through the universe.

Objects attract each other.

The more massive the object,
the greater the pull.

Scientists call
this force gravity.

If the universe is a symphony,

then gravity
is its great conductor.

It choreographs the dance
of everything in the cosmos.

It brings clouds of gas
together to form stars,

stars together to form galaxies,

and galaxies together
to form clusters,

including the great wall.

It sounds simple.

Gravity pulls objects together

into ever larger structures.

But there's a big problem
with this idea.

From the big bang...

...to the galaxies
that we see today,

computers can simulate
how the cosmos evolved.

When scientists simulate
the formation of superclusters,

these megastructures
end up loose,

as gravity isn't strong enough.

Only when they boost the gravity
beyond the expected level

does matter assemble fast enough

to form the superclusters
that we see today.

So how can objects like
the great wall form

if gravity is too weak?

The only force in the universe

that we know that brings things
together is gravity.

When it comes to structures
as large as the great wall,

there just isn't enough gravity
in the galaxies together

to form something that huge.

Something else must be there
underlying all of it,

creating more gravity
than we can account for.

Where is the missing
gravity that the universe needs

to make the great wall?

And is the great wall unique,

or is it part of an even
larger cosmic structure?

The boss great wall is
a vast collection of galaxies

that stretches over one billion
light-years across.

Scientists calculate
that the gravity

of its thousands
of galaxies alone

is too weak to build
this immense megastructure.

Where does the extra gravity

that's needed to construct
the great wall come from?

Scientists believe that a clue

lies in the space
around galaxies.

Gravity doesn't just
pull on matter.

It also bends light.

When powerful telescopes

photograph
dense galaxy clusters,

the objects around them
look distorted.

This warping of space-time

by a giant cluster of galaxies
can act like an optical lens

that magnifies the light
of galaxies beyond it.

These strange,
smeared-out images

all over the sky...
These are real.

This is actually
what you would see

if your eyes
were sensitive enough.

You would see this
in the night sky.

But sometimes,
something weird happens.

The light that comes
from behind galaxies

bends far more
than astronomers expect.

There must be
an invisible material

with huge mass and gravity
around these galaxies.

This material could unlock where
the extra gravity comes from

to build megastructures
like the great wall.

Scientists call it dark matter,
and they estimate

that it outweighs regular matter
by a factor of 5 to 1.

Dark matter
permeates the universe.

We can't see it, but we know
it's there through its effects.

It has gravity.

And if it has gravity,
it must have mass.

If it has mass, it must be made
of matter that we can't see,

hence the name.

The question is, what is it?

The fact that
dark matter appears to have

weight is evidence that it is
some kind of particle.

If dark matter
is made of particles,

then physicists
should be able to find it.

Today, teams around the world
hunt for this strange matter.

This is the largest
dark-matter detector on earth.

It is called the LZ experiment.

It sits in an abandoned
gold mine

one mile beneath south Dakota.

The strange properties
of dark matter mean that

it is one of the few
types of particle

that can pass through solid rock
to reach this tank.

Inside the tank
are 10 tons of liquid xenon.

This dark-matter
experiment uses xenon

because it's really stable,
it's not radioactive,

it doesn't undergo
chemical reactions.

So if something happens
in that xenon tank,

it has to be external.

The theory is that
certain types of dark matter

will hit a xenon atom and create
a characteristic flash of light.

And if we see one of those,

we have our
dark-matter smoking gun.

The discovery of
dark matter will finally prove

what creates the extra gravity
that shapes the universe.

It could also help explain
the evolution

of cosmic megastructures
like superclusters

and the great wall.

In the early universe,

it is possible
that dark matter condenses

and begins to flow

to form a gigantic
irregular matrix.

Its massive gravity
draws in the first atoms

and newly forming matter
in the cosmos.

More and more matter
condenses onto this scaffold,

and its gravitational pull
gets stronger.

So this is where stars
and galaxies form.

They cling to their
invisible frame of dark matter

in huge structures

like the great wall's
superclusters.

Dark matter is needed
to give structure or scaffolding

to something like
the great wall.

Dark matter is the critical
missing ingredient

for our understanding of how
the universe actually works

and how structure grows
and evolves within it.

Dark matter solves the riddle

of how the great wall
gets its distinctive shape.

But is the great wall unique?

Astronomers scan
the cosmos for clues.

They discover that
the great wall is not alone.

They find similar
cosmic megastructures

lurking in the depths of space,

like this...
The Sloan great wall.

Its five stretched-out
superclusters contain

an estimated 6,000 galaxies.

This wall is huge.

But it is only around 1/2 as
massive as the boss great wall.

We're calling this
the great wall,

but it's really
the biggest great wall.

We know of about a dozen others,

and these are
immense structures.

What is the link
between these great walls?

Astronomers race to find
the connections

between these megastructures.

But seeing these links
is a big challenge.

Matter produces light in places
where it is dense enough

to form stars and galaxies.

But precisely what lies
in the dark spaces

between these bright spots
is a mystery.

So little of
the universe is actually bright,

glowing with starlight,

and yet that's really
the only thing we can see

in the distant reaches of space.

So we see these galaxies
beginning to line up,

but we don't really see
the underlying structure.

They're kind of like little
fairy lights on a string,

but we can't actually connect
all the little bright dots yet.

In 2019, the
very large telescope in Chile

makes a vital discovery.

It captures an image
of a cluster of young galaxies

12 billion light-years
from earth.

The young galaxies'
newborn stars burn super bright.

Their intense light illuminates
areas of space

that are normally
too dark to see.

This cosmic flashlight shows
that immense clouds of hydrogen

fill the space between galaxies.

Discovering this material

was an absolute game-changer

because it allows us to see
structure in the universe

on galactic and intergalactic
scales for the very first time.

Astronomers think
that vast, invisible clouds

of hydrogen like these
run between all galaxies.

But how do gas and dark matter
weave together

megastructures like great walls

that are separated
by billions of light-years?

And what shape is this
giant cosmic network?

In 2016,

astronomers discover
the boss great wall.

They suspect that it links
to similar structures spotted

throughout the cosmos.

But how do these
megastructures join together?

A clue lies in the way
that the gravity of dark

and regular matter shapes
the superclusters

that make up these great walls.

When you think about
things pulling together

under the force of gravity,

you would assume the universe is
very good at making big blobs,

everything just orbiting
around everything else.

But at the scale
of superclusters,

the galaxies form
very interesting,

very well-defined shapes.

The observable universe

contains an estimated
10 million superclusters.

The galaxies in 70 percent
of these structures

appear to line up
in long shapes called filaments.

Astronomers believe that
a quirk of gravity

unlocks why so many
are this shape.

The big bang scatters energy
across the universe,

where it condenses into huge,
elongated clouds of matter.

Gravity squashes an
elongated cloud to a point

where dense areas collapse
to form stars and galaxies.

Next, gravity attracts
the densest parts of the cloud

to each other.

The gas and galaxies
flatten into a sheet.

Gravity then draws together
the densest parts of the sheet

to eventually form
long filaments.

Astronomers think that
the way gravity molds gas

and dark matter on a huge scale

provides a clue about
how the great wall

joins to the wider universe.

Starting soon
after the big bang,

gravity sculpts the gas and
galaxies of the early universe

into sparkling, tube-like
superclusters.

The bright galaxies
inside four superclusters form

the distinctive shape
of the great wall.

But the great wall may not
float alone through space.

Its superclusters could stretch

for many more millions
of light-years

and intersect with similar tubes
of gas to make a cosmic web

of which the great wall
is merely a part.

Galaxies are not randomly
strewn throughout the universe.

They form into superclusters.

Superclusters aren't
randomly strewn

throughout the universe, either.

They form a pattern,
a web of filaments.

This pattern is telling us
about how the universe

is built on an immense scale.

The superclusters
in the great wall

could be just the bright,
visible sections of super long,

invisible threads of gas
and dark matter

that crisscross the universe.

What is the shape
of this cosmic web?

Researchers at the university
of California, Santa Cruz,

believe that one of earth's
strangest creatures

might unlock the mystery.

This is a slime mold.

The entire organism consists
of a single giant cell.

Slime molds thrive on bacteria
and rotting matter.

But this food is spread out.

So this strange organism
has a cunning strategy

to scavenge the greatest area

using the least amount
of energy.

It grows a feeding network.

A slime mold is
a very simple organism

that lives
in decaying vegetation.

They actually send out
little tendrils.

The tendrils connect, and
the slime mold grows over time,

so you have this larger,
web-like structure evolve.

The researchers
believe that the algorithm

the slime mold uses
to search for food

could predict how the universe
weaves great walls

into a cosmic web.

The researchers decode
the algorithm

that the slime mold uses
to build its network

and inject it into a 3D model
of 37,000 nearby galaxies.

This is the result.

The virtual slime mold
sees the galaxies as food

and builds a network
between them.

This network predicts the exact
paths of the invisible filaments

of gas and dark matter
that link the universe together.

But does the slime mold match
the pattern of the real cosmos?

And how big can the great walls
in this giant web get?

The boss great wall
is the largest structure

ever seen in the universe.

Many astronomers believe

that it is part of a larger
network of gas filaments

that weave superclusters
into a vast cosmic web.

One theory is that the way
a simple slime mold

grows its feeding network

can predict the actual layout
of these filaments.

But can a single-celled
organism on earth

really reveal the shape
of the cosmos?

There is a way to find out.

The Hubble space telescope
photographs

nearly 1,000 quasars
between 1990 and 2020.

Astronomers think that quasars
are supermassive black holes

at the hearts of
distant galaxies.

The massive gravity of quasars

superheats the matter
that gets close to them.

This energy produces
an intensely powerful light.

Some of the predicted
gas filaments

sit directly in front
of a quasar.

The pictures from Hubble show
that the light it sees

coming from these quasars
is dimmer than expected.

This is strong evidence
that invisible gas filaments

block some of the light.

The cosmic web that links
superclusters and great walls

across the universe really could
be the shape of a slime mold.

The universe really
produces some weird connections.

And one of the weirdest is
the fact that the networks

and connections that the
slime molds make with each other

looks a lot like what we see
in a large-scale structure.

Scientists do not know
for sure why the slime mold

and the universe
grow into similar shapes.

Both networks appear to follow
a hidden mathematical rule

that allows them to fill
the maximum volume of space

with a limited amount of matter.

Astronomers believe that
great walls are the largest,

densest patches of galaxies
and gas in a vast cosmic web.

And thanks to the tiny
slime mold, we can now see

how these vast megastructures
connect across the universe.

The boss great wall is huge.

But is there something
even bigger out there

waiting to be discovered?

Astronomers think that the
answer hinges on the outcome

of a battle between two forces
that shape our universe.

The first force is
the pull of gravity.

Gravity attracts
things together.

And not just that,
the closer you are to something,

the stronger
the gravitational force.

So all across space,

you're attracted
to your nearest neighbor.

That builds up structure
from galaxies

to clusters
to superclusters and larger.

The second force
is the push of the big bang.

On the very largest scales,

we have the force of expansion

left over
from the big bang itself

that has caused
the universe to grow

93 billion light-years across
over the last 14 billion years.

The universe will build

ever more massive structures

if gravity beats
the force of expansion.

But structures can't grow bigger

if expansion pushes matter
out of reach faster

than gravity
can gather it together.

Finding a structure greater
than the great wall

rests on unlocking which of
these two factors

is the more powerful.

And so to figure out
how much pulling together

and pushing apart there are,

we need to make
a very precise measurement

of the expansion rate
of the universe.

Astronomers at
Arizona's Kitt peak observatory

get a front-row seat
at this cosmic contest.

This is the Mayall telescope.

It measures the distances
between thousands of galaxies.

Astronomers compare the average
distance between galaxies today

with the distance
between galaxies

in the younger parts
of the universe.

This comparison charts
the speed of the expansion.

The data from
the Mayall telescope

reveals something extraordinary.

The expansion is getting faster
and faster over time.

This acceleration
puts ever greater distances

between the matter
the universe needs

to build superclusters
of galaxies.

This means that there is a limit
to how big great walls can get.

It is possible
that the boss great wall

is the largest structure
in the universe.

Why is the expansion
of the universe accelerating?

And what does it mean for the
future of the boss great wall?

The boss great wall
is the largest collection

of galaxies ever discovered.

And many astronomers think
that its size

is the largest that
any structure will ever grow to.

The reason is the discovery that
the expansion of the universe

is getting faster and faster

and driving galaxies
further apart.

Why is this expansion
accelerating?

A clue lies in what happens
in the coldest, darkest,

and emptiest parts of space.

In 2019, scientists
in Zurich, Switzerland,

detect tiny energy fluctuations
in a vacuum chamber

chilled to just
above absolute zero.

These bursts could come
from strange exotic particles

that pop in
and out of existence.

Their energy produces
a tiny outward force,

like a small push
on the fabric of space itself.

In places where
there is lots of matter,

like around planets,
stars, and galaxies,

these minute effects
go unnoticed.

But in empty regions of space,

like the voids between
the threads of the cosmic web,

it could be a different story.

This whole time, we've been
letting our eyes be drawn

to the bright parts
of the universe,

this beautiful cosmic web
that stretches across space,

but if you look
in between the filaments,

there are these vast voids
where there is almost nothing.

And could it be that
very empty regions of space

behave in some fundamentally
different way?

Scientists pin this
different behavior onto a weird

hidden force called dark energy.

The way dark energy works
could explain

why the expansion
of the universe is accelerating.

The tiny push from dark energy
expands the space around it

like an oil bubble
growing in clear water.

This new space
contains dark energy,

and the push from
this new dark energy

creates even more new space.

This never-ending cycle
continuously increases

the amount of dark energy.

The expansion
of the universe accelerates,

and this could signal the end

for structures
like the great wall.

As the mega voids grow,

they flood the space around them
with dark energy.

And the great wall is
right in the firing line.

The dark energy rips
the superclusters

from the great wall.

And tears them apart.

The dark force is so strong

that it shreds superclusters
into their building blocks.

Eventually, the galaxies
themselves disintegrate.

They leave stars and planets
drifting alone through space

with skies devoid of starlight.

We live in a special time
in the universe...

The era of superclusters.

The universe is expanding.

Moreover, we think that
that expansion is accelerating.

It's expanding faster
and faster every day.

This spells doom
for the great wall

because eventually dark energy
will tear clusters apart.

The great wall is
a wonder of the cosmos.

It is a vast assembly
of gas and galaxies

that stretches over a billion
light-years of space.

Even though
the great wall is one of

the largest known structures
in the universe,

it's so ephemeral
and so easy to miss,

and so its actual
discovery has been

one of the great achievements
of observational astronomy.

Astronomers now know
that the great wall

is just one small part
of a network

that holds everything
in the universe together.

A giant cosmic web
of trillions of galaxies

stretching billions of
light-years across the universe,

filling the entire space.

It's just mind-blowing.

Quantum fluctuations
frozen in time

trillionths of a second
after the big bang

lay the foundations
of the great wall.

Dark matter then chisels out
the megastructure

when the universe is young.

Dark energy threatens to tear it
down billions of years from now.

The universe appears to
be almost ripping itself apart.

Even superclusters,
even clusters of galaxies,

may not survive dark energy.

We have never seen
anything quite like

the great wall.

And we may never see anything
quite like it in the future.

But while it lasts,

it is one of the biggest
highlights of the cosmos.

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