Space's Deepest Secrets

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?

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.