Space's Deepest Secrets (2016–…): Season 8, Episode 2 - Space's Great Wall - full transcript
Astronomers discover a cosmic structure one billion light years long.
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.
captions paid for by
discovery communications
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?
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.
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.
captions paid for by
discovery communications
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?
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.