Original subtitles

NARRATOR: First there was light,

visible light.

Then we viewed the universe in radio waves and X-rays.

Ever since there's been astronomy,

we've been looking at different kinds of light

and opening up the universe a little bit more at a time.

But then in 2015, like, the roof came off.

Something happened that changed everything,

the ability to see waves in space and time itself.

Gravitational waves.

They help us roll back the clock to the dawn of time...

..discover epic cosmic collisions...

..and make earth-shaking discoveries.

Gravitational waves are the biggest game changer

since the invention of the telescope.

We have a completely new universe to view now.

A new exploration of space is just beginning.

(EXPLOSION)

Long ago, 17 billion light years away,

a cataclysmic showdown plays out.

Two black holes lock together in a deadly cosmic dance.

Black holes are unimaginably dense objects

with gravity so intense

that if you get too close to them, you're gone.

Their immense gravitational pull

causes them to spiral towards each other.

When black holes collide, they don't just run into each other,

they are in orbit about each other.

So, what we're talking about is an in-spiralling orbit

that goes faster and faster and faster and faster...

..until they finally collide in a fatal embrace.

(EXPLOSION)

But astronomers don't see a thing.

The problem with observing colliding black holes

is all about the name, black holes. They give off no light.

How can astronomers see something that no telescope can detect?

Across the universe, extraordinary events take place.

But we sometimes miss them because we rely on light.

Now, astronomers have a new tool kit

that's revealing the cosmos in a totally different way.

Using the very fabric of our universe we call spacetime.

Everything with mass, like stars,

planets, and black holes, all curve this fabric.

The more massive the object,

the bigger the distortion of spacetime.

The classical analogy is this stretched rubber sheet, right.

And like a mass, like the sun is like a ball on the sheet

and it distorts and warps the sheet into this valley, right.

And if you roll a marble across it, like the marble's a planet,

the marble will be pulled into orbit around the ball

because of the curvature of the sheet.

But that's only half the picture.

If an object has mass and is accelerating through spacetime,

it creates ripples in that fabric of spacetime,

and we call these gravitational waves.

Gravitational waves give us vital clues

about distant objects that we can't see.

The more massive the object that produces them,

and the faster it's moving, the bigger the ripples.

These ripples pass through planets, stars, and galaxies with ease.

When a gravitational wave passes through an object

like a star or a planet or a person,

it stretches and compresses them, like with this tennis ball.

Now, if you're close to a powerful source of gravitational waves,

like merging supermassive black holes,

those waves are incredibly strong,

and they're capable of actually destroying a planet.

But, like the ripples on a pond,

their strength and size diminishes over distance.

The farther away you are, the weaker they get.

And when they're hundreds of millions of light years away,

they're actually smaller than the size of an atom.

So, to listen for gravitational waves,

scientists built the most sensitive measuring device on the planet.

This is LIGO,

the Laser Interferometer Gravitational-Wave Observatory.

Two enormous detectors

located almost 2,000 miles apart in Louisiana and Washington state.

Each sensor has L-shaped arms, measuring 2.5 miles.

Inside the LIGO detectors,

inside these concrete tunnels,

there is a laser system.

It's called an interferometer.

So, light comes in from a laser beam

and is split into two paths.

Normally, the lengths of the two beams are the same.

That changes when gravitational waves

hit the beams.

When a gravitational wave passes through,

it changes the distance that light travels along these arms.

So, one arm effectively gets longer, and the other one gets shorter.

The length of those two beams varies just ever so slightly

and the very sensitive apparatus in LIGO is able to pick that up.

With this ultra-sensitive laser system,

LIGO picks up distortions in spacetime,

narrower than one millionth of the diameter of an atom.

Just that feat, just the fact that we were able

to build a detector to detect gravitational waves

is just mind-boggling.

All of a sudden now, we're listening

to the faintest whispers of the universe.

In 2015, LIGO picked up a whisper

that had been travelling towards Earth for over a billion years.

Its source? Two colliding stellar black holes.

Watching two black holes spiral in and merge,

that's not something we can do using optical telescopes

or X-ray telescopes or anything like that.

But, with LIGO, we could actually detect that event.

Now, scientists can paint accurate pictures

of invisible objects.

You can tell you are looking at black holes,

you can get their masses, you can get their distance.

There's a phenomenal amount of information in that wave.

The colliding black holes are the most massive

LIGO has ever detected.

One is 66 times the mass of our sun.

The other, 85 times the mass of our sun.

As two black holes are spiralling in,

they are moving faster and faster as they get closer and closer.

That means that the gravitational waves they are emitting

have a higher and higher frequency.

So, as time goes on, the pitch gets higher.

So, it goes oohrup!

Oohrup! Oohrup!

(BEEPING)

When they finally merge, they create a giant.

By analysing that data,

it's possible to establish that the new black hole

from the merger of these two original black holes,

weighs as much as something like 140 times the mass of our sun.

It's difficult to overstate the importance of gravitational wave detection.

It's like adding on an entirely new sense.

All of a sudden, there's a brand new way

to explore the rest of the universe.

Invisible cosmic collisions are just the beginning

of what gravitational wave astronomy can reveal to us.

Now, scientists are using gravitational waves

to revisit other long-standing mysteries.

Like, what causes the brightest explosions in the cosmos?

This is not an everyday car crash.

This is the most dramatic event

that you're ever gonna see in our universe.

Across the universe, strange bursts of light puzzle astronomers.

For just a fraction of a second,

they shine more than a trillion times brighter than the sun.

Then, they vanish.

These brief flashes of light are known

as gamma ray bursts or GRBs for short.

And they're such a mystery because they are insanely energetic,

and we don't know what causes them.

For decades, these short gamma ray bursts have been an enigma.

No explanation was off limits, no matter how wild.

Is it a supernova? Is it an alien civilisation saying hello?

You know, we just don't know.

In August 2017, the Fermi Gamma-ray telescope

detected another short gamma ray burst.

But this one was different.

So, a gamma ray burst went off 130 million light years away,

and it actually produced a ripple in space and time

that LIGO could detect.

Gravitational waves could help finally reveal

what causes one of the brightest explosions in the universe.

LIGO's data suggests the culprit could be two massive objects,

spiralling towards each other and colliding.

But based on the gravitational wave data,

these two objects were too small

to be black holes, they had to be something else.

Not black holes

but the ultra-dense cores of collapsed stars

called neutron stars.

A neutron star is what's left over

after a massive star collapses in on itself.

It's very, very dense,

because it took all essentially the mass of the core,

and contracted it into a really, really small radius.

As the dense neutron stars spiral ever closer,

the gravitational wave signal gets stronger and stronger.

Until they collide,

releasing an epic burst of gravitational waves.

Because they're not black holes, light can get out.

And if you smash two things together,

at these kind of absolutely massive speeds,

there's a huge amount of energy involved.

Energy we detected both as invisible gravitational waves

and visible light.

Could this light be a mysterious and ultra-powerful gamma ray burst?

How could these colliding dead stars

be associated with gamma ray bursts,

which are in fact the most energetic explosions we see in the entire universe?

Neutron stars have powerful magnetic fields

that trap particles of gas and dust.

During a collision, the swirling magnetic fields twist up,

building up more and more energy.

You have lots of little particles of matter

that are trying to keep up with these rapidly spinning magnetic fields,

that starts swooshing them round

until they reach pretty much the speed of light,

and eventually they're kind of shot out of the remnant

in a tight beam.

The beam is a gamma ray burst.

But they're not always easy to detect.

If the jet coming out is pointed right at you,

then you see this extremely high-energy event,

a gamma ray burst.

If it's not pointed at us, we might miss it.

Fortunately, the gravitational waves show us where to look.

Following the gamma ray burst, we spotted a strange red cloud.

Evidence of a heavy element factory.

PAUL: After the initial collision, there is a shell of debris

moving outwards.

But then, high-energy neutrons come slamming into this material

and start to build heavier elements one after another.

We can see the gold,

we can see the potassium, we can see the plutonium

being created before our very eyes.

The neutron star collision produced huge quantities of heavy elements,

blasting out enough gold and platinum

to weigh more than ten times the mass of the Earth,

solving a long-standing mystery.

We knew that supernova explosions

did create some of the heavier elements.

But from everything we've observed about supernova,

they don't happen often enough

to really populate a galaxy with all of the heavier elements that we observe.

This was the missing piece.

The gold on your wedding ring,

the gold in your jewellery

was formed and forged from a titanic collision

before the Earth even existed.

The combination of gravitational waves and telescopes...

..proves that neutron star collisions create precious metals...

..and cause super bright gamma ray bursts.

When you can measure a gravitational wave signal

and a light signal like a gamma ray burst,

you get a whole new way to solve

complicated, intertwined physical processes.

It's like you're watching a symphony on mute,

and then you hit that button and the sound comes on,

and it's just a completely different picture.

The sounds of the cosmos don't just reveal collisions.

It turns out, we can use gravitational waves

to help us understand some of the biggest mysteries

of the cosmos.

Every new way we figure out

to probe the universe is a good thing.

And detecting gravitational waves,

it's a new dimension to being able to study the universe.

It's like, it's like having a new sense.

This new sense could be just what astronomers need

to answer some of the biggest questions in physics.

Like, what is the speed of gravity?

And does it travel at the universe's speed limit?

One of the things we learn early in science is that the universe

has an absolute speed limit,

which is the speed of light in a vacuum, which is 186,000 mi/s.

Light from the sun takes eight minutes and 20 seconds to reach Earth.

So, if the sun disappeared,

we wouldn't miss its light immediately.

But how quickly would we notice its missing gravity?

The first thing that we'd notice is nothing.

Things would seem very normal. But then they wouldn't.

There would be nothing curving space where Earth is located,

and so Earth would take off in a straight line,

moving at the same speed at which it orbits the sun.

And things will get cold and lonely really, really fast.

According to Albert Einstein, our skies would go dark,

and the Earth would be flung into deep space

at exactly the same time.

It's a foundation of his famous Theory of Relativity,

still the most complete theory of how our universe works.

Einstein's Theory of Relativity has been a fantastic theory.

It explains so many things for us, including gravity.

But when we look out at the universe, there are many mysteries.

There are things that are quite hard to explain.

At the top of the list, the mystery of our expanding universe.

There is something pushing outward

that is making that expansion rate ever and ever faster.

Astronomers call this "something" dark energy.

It accounts for 70% of the total energy in the universe.

Einstein's models of the universe need dark energy to work.

But we have no idea what it is.

Dark energy is not something we actually understand.

It's kind of a placeholder term for something we don't understand.

And so, people, naturally, are looking for better theories.

Theories that are a bit like Einstein's theory,

but just go that bit further and explain

some of these things that we don't currently understand.

One way to excise dark energy is with a new theory of gravity.

One where the speed of gravitational waves

is different from the speed of light.

There are some so-called "non-Einsteinian theories"

for the structure of spacetime itself,

that don't actually require dark energy.

For example, if gravity doesn't propagate through spacetime

at the same speed that light does,

you could find models that don't actually require dark energy.

It could be a clean, simple,

albeit very, very profound solution, to this underlying problem.

In order to overthrow Einstein, and eliminate dark energy,

the speeds of light and gravity must be different.

We know the speed of light.

So, how do we test the speed of gravity?

In order to test the speed of gravity,

you need to have a system that emits both gravitational waves and light.

The colliding neutron stars detected by LIGO in 2017

are part of the solution.

The collision released a flash of light

along with a burst of gravitational waves.

But the universe threw a curve ball.

The light signal arrived 1.7 seconds after the gravitational wave signal.

Does that mean gravitational waves travel slightly faster than light?

Albert Einstein predicted

that gravitational waves would move at the speed of light.

So, what if Albert Einstein was wrong?

I know, sounds crazy, right?

That's like almost as crazy as me being wrong, right?

But if Einstein was wrong, that's one thing,

but a bigger problem is that we'd have to rethink our physics.

Before we do that, let's take a closer look

at the neutron star collision site.

It's surrounded by a shroud of gas and dust.

Light is made of particles called photons,

which scatter when they hit obstacles.

But gravitational waves pass through anything.

They pass right through everything like it's not there.

Light, on the other hand,

was slowed down by interactions with that matter.

It didn't just escape immediately

like the gravitational wave signal did.

The debris gave the gravitational waves a head start

by slowing the light.

So, gravitational waves and light do in fact travel at the same speed.

Einstein was right.

This one event ruled out the other theories of gravity

that are competing with Einstein's theory.

Things that people have been working on all their life,

and overnight, it's gone.

Thanks to gravitational waves,

dark energy remains our best explanation

for why the universe's expansion is accelerating.

Maybe dark energy isn't what we think it is.

And maybe tomorrow, or maybe next year,

or maybe next decade, or next century,

we'll discover that.

Gravitational waves are a huge step forward

in our effort to understand the universe.

And I mean everything. Space, time, matter, dark energy.

We have a completely new universe to view now.

Now, astronomers want to use gravitational waves

to answer another mystery.

What happens when supermassive black holes collide?

We first detected gravitational waves in 2015.

Since then, they've revealed colliding black holes

across the universe.

Prior to LIGO going online,

we'd never witnessed black hole collisions directly.

But now that we can witness them with our observatories,

we're finding them pretty regularly.

We're seeing gravitational waves

come across the LIGO experiment left and right.

But LIGO has only been listening for gravitational waves

from black holes on the smaller end of the cosmic scale.

When we look at the cosmic zoo of black holes out there,

we find small ones

weighing, you know, ten, maybe 30 times as much as the sun.

And then large all the way up to extra-large,

going from like a million to a billion times as much as the sun.

These "supermassive" black holes lurk at the hearts of galaxies.

When galaxies merge, supermassive black holes should merge, too.

But even though we see galaxies colliding across the universe,

we've never seen two supermassive black holes collide.

Because they have too much orbital energy

to get close enough to merge.

That orbital energy has to go somewhere.

And what supermassive black holes do

is they throw out stars that are around the core of the galaxy.

But when they get sufficiently close,

there are just no more stars to throw out.

And, so, the idea is, they can't merge.

So, there's a problem. How is it that they manage to bridge that gap

and finally spiral in?

The only way to understand if supermassive black holes merge

is by looking at their gravitational wave signal.

Two supermassive black holes merging

should release a burst of gravitational waves

millions of times more powerful than a stellar mass

black hole merger.

But LIGO won't hear a thing.

The problem with using LIGO to detect the merger of supermassive black holes

is actually a scale of time.

One wave, as these things move around each other very slowly,

will take over ten years to go by. Just one wave.

In order to detect a gravitational wave with periods of decades,

you also need an experiment

that can be extremely stable over that amount of time.

Vibrations from earthquakes, weather, or even nearby traffic,

prevent LIGO from listening for a decade,

just to hear one wave.

But there may be another way to detect

gravitational waves from supermassive black holes.

Using a strange type of dead star called a pulsar.

A pulsar is a kind of neutron star

that is rapidly spinning and has a beam of radiation

that makes wide circles across the sky.

And when that flash of circle washes over the planet Earth,

we get a little beep, a little beep.

We get pulses of radiation, hence pulsar.

Pulsars are the best timekeepers in the universe.

But passing gravitational waves make them miss a beat.

What if we noticed that the frequency of a pulsar was shifting

very, very slowly, year to year to year,

over ten years or more,

just slightly getting a little bit longer,

as space itself was changing between us and the pulsar?

By monitoring dozens of pulsars,

Chiara Mingarelli and a team of astronomers

have created a galaxy-sized gravitational wave detector.

It's called a pulsar timing array.

You can really look for deviations in those arrival times over decades.

Almost like a tsunami warning system

to show you when a gravitational wave is passing by.

After 12 years, the team detected

the same change in a number of pulsars.

These pulsars are all thousands of light years apart.

If you think about it, it's difficult to make

a signal that's the same in all of these pulsars.

This has to be this common signal

from something like a gravitational wave event.

The signal the team detected wasn't created

by just two supermassive black holes colliding.

It's evidence of gravitational waves

from hundreds of pairs of supermassive black holes,

all in different stages of merging.

Because it takes so long

for one of these individual binary systems to merge,

there could be thousands, if not millions,

of these signals all being emitted at the same time.

All of them. They all create this gravitational wave background

that we're just starting to see the first signs of now.

Astronomers predict this gravitational wave background

fills our universe.

If the signal the team detected is confirmed,

it's proof that supermassive black holes do merge.

The next step is to observe that as it happens.

It would be a dream to see

two supermassive black holes merging,

emitting gravitational waves,

and also being able to point a telescope at them

and to see the physics of how they merge.

Gravitational waves reveal the hidden workings of the cosmos.

They reach the farthest corners of our universe.

Now, astronomers are using gravitational waves

to look back in time.

They'll let us see all the way back

to the earliest moments of our Big Bang.

(EXPLOSION)

13.8 billion years ago...

..the universe sparks into life.

The tiny speck of energy expands and cools.

The infant cosmos is a fog of tiny particles of matter.

Over time, the particles form atoms of hydrogen and helium.

The fog clears and the first light races across the universe.

We call that light the cosmic microwave background.

The Cosmic Microwave Background is simply the most distant light we can see.

So, looking at it gives us baby pictures of our universe,

the way it looked 400,000 years after our Big Bang.

What happened before these baby pictures remains a mystery.

The leading theory is that in the very first second of the Big Bang...

..our infant universe had a growth spurt.

Scientists call this idea inflation.

In a billionth of a billionth of a billionth of a second,

our universe grew a billion, billion, billion, billion,

billion, billion times bigger.

That is the mother of all growth spurts.

It laid the foundations for the entire cosmos

that we know today.

Inflation is just a theory.

But there may be a way to prove it happened.

Scientists think that during that brief moment of cosmic expansion,

inflation stretched tiny fluctuations of gravity.

That is such a violent process that it actually

causes ripples and distortions

in the very shape and fabric of space itself,

which we can see today as gravitational waves.

Scientists call these theoretical ripples

through the early universe primordial gravitational waves.

When they were first released, these were deafening.

But in the billions of years since,

our universe has grown bigger and colder,

and these gravitational waves have diluted

so that they barely even exist today.

Scientists searched for signs of these very weak,

primordial gravitational waves in the cosmic microwave background.

And in 2014, a team, using their purpose-built microwave array

in Antarctica called BICEP, found a strange, swirling pattern.

When they saw those swirls, they saw those patterns,

they thought they had seen the signature

of primordial gravitational waves.

Now, this is really the conclusive evidence

that inflation had to have happened.

The results were exciting. But there was a glitch.

This amazement lasted...

for a few months until cracks

started to appear in this, and gradually it all collapsed.

The signal, thought to be proof of primordial gravitational waves,

and the theory of inflation,

turned out to be a case of mistaken identity.

As this light from the ancient universe,

from the cosmic microwave background,

travels through the universe, it had to travel

through dust before reaching our detectors.

And the dust itself

can affect the light

and mimic what the primordial gravitational waves can do.

The primordial gravitational wave signal

turned out to be mainly clouds of dust floating through space.

That's how BICEP bit the dust.

BICEP failed to detect primordial gravitational waves.

Can LIGO do any better?

Everything changed in 2015

with that announcement of first detection

of gravitational waves.

That is one of the great triumphs in all of science.

We have broken through the electromagnetic window on our universe.

And we've moved into the gravitational wave.

Ladies and gentlemen,

we have detected gravitational waves.

We did it. (APPLAUSE)

They were jumping up and down, they were crying, they were smiling.

The first LIGO detection of two black holes spiralling in and merging

and emitting these gravitational waves

was a very big deal.

This was the very first time gravitational waves

had ever been directly detected.

And we've been trying for, like, half a century.

Einstein predicted this in the early 20th century.

And it took us literally 100 years

before we could detect them for the first time.

I'm getting goosebumps just thinking about that.

We really had found a gravitational wave.

HAKEEM: Unfortunately, LIGO can't help us

in observing primordial gravitational waves.

It can't even observe supermassive black holes at the centres of galaxies.

It is designed to observe in a particular frequency range.

Primordial gravitational waves are at such a low frequency

and such a low amplitude,

that there is no hope of LIGO being able to detect them.

But scientists hope that an ambitious project

called LISA will.

Not on Earth but from 30 million miles above.

LISA is like LIGO but bigger and in space.

LISA, or the Laser Interferometer Space Antenna,

will be a system of three satellites,

arranged in a giant triangular formation

1.5 million miles apart.

If a gravitational wave passes through them

and changes that distance, they can detect that.

Because the satellites are so much farther apart,

a very low frequency wave can make a detectable change.

LIGO wouldn't be able to see that but LISA could.

As well as listening for low-frequency gravitational wave sources

like supermassive black hole mergers,

LISA will listen for primordial gravitational waves

from the dawn of time.

If it detects them, we will know that the infant universe inflated.

Inflation has explained

almost everything we measure in modern cosmology.

It's an incredibly successful theory.

The icing on the cake will be if we could also discover these

gravitational waves that it's supposed to have created.

From the Big Bang, to the most massive black holes,

the universe talks to us using gravitational waves.

Just like with telescopes,

we're using gravitational waves

to look at different types of objects,

neutron star mergers, and black hole mergers,

and learn more about the universe around us.

They could even reveal the most elusive substance

in the universe. Dark matter.

If anything's gonna help us

understand the nature of dark matter,

it might just be gravitational waves.

Across the universe, an invisible substance

holds galaxies together.

Without it, they would fly apart.

The Milky Way should have dispersed long ago.

And the Magellanic clouds right in front of us are exactly the same.

These things should be just shedding stars left and right

as they fly off this rotating galaxy.

Instead, they're not, they're holding together.

There are motions in the stars that we just cannot account for

unless there's something holding the whole thing together.

We call this mysterious substance dark matter.

It doesn't interact with light, so we can't see it.

But we cannot ignore it.

From the motions of stars inside of galaxies,

to the motions of galaxies inside of clusters,

to the very structure of the universe itself,

we see evidence for dark matter everywhere we look.

We think dark matter makes up 85% of the matter in the universe.

But because we can't see dark matter with telescopes,

we know very little about it.

While we know that it's there,

we haven't actually answered the question of what it is,

or how it interacts, or why it's there, or how it's created.

So, you have to be really creative,

if you want to go after this stuff and really understand what's it made out of.

One creative theory suggests that black holes make up dark matter.

Not the regular stellar mass black holes that LIGO detects.

Or the supermassive black holes that lurk at the centre of galaxies.

But tiny primordial black holes,

born during the period of rapid expansion

in the first moments of the Big Bang.

Primordial black holes could be potential explanations

for what we call dark matter.

And if there's enough of them, they can hold an entire galaxy together.

But we don't know if primordial black holes exist.

But gravitational waves could change that.

When you form a primordial black hole,

you send out a burst of gravitational waves

that, in principle, carries on travelling through the universe

and you might be able to detect it, still today.

The problem is that these things would have emitted gravitational waves

at a frequency that is not detectable by LIGO.

And, so, it's very hard to discern

whether or not they are plentiful enough

to actually serve as a compelling dark matter candidate.

But some scientists have a radical idea.

Could LIGO have already spotted that?

LIGO's detection of black holes,

more than 50 times the mass of our Sun,

could provide tantalising evidence.

We expect stellar mass black holes

to be up to maybe 10 or 20 times the mass of the sun.

We know that they are born from the deaths of massive stars,

and so the mass of the parent star

sets a limit to how big the black holes can be.

Some scientists are wondering,

could these black holes already detected by LIGO in fact

be primordial black holes grown up?

Could we have already detected a form of dark matter?

It's possible that tiny black holes

could have been formed in the early universe.

And then slowly over time, they snack on gas and dust

so that over the course of billions of years,

they become 10 to 50 times the mass of the sun.

And there's one more piece of evidence.

Because stars themselves are spinning,

black holes that are born from stars must also spin

because you can't get rid of the spin.

But the black holes that LIGO discovered merging

didn't have a lot of spin.

And that's a very curious situation.

Even more curious, is the fact that primordial black holes

born from collapsing spacetime in the early universe

shouldn't spin either.

Is it possible we've detected a grown-up primordial black hole?

It's definitely a speculative idea.

But on the other hand, physics definitely turns up

very weird things from time to time,

so you can certainly say stranger things have happened.

If primordial black holes do exist,

they still might not explain all the dark matter

in the universe.

They might be working with another type of dark matter

to hold galaxies together.

The upcoming LISA mission may fill in the blanks.

What we call dark matter could be simple.

It could just be made of one thing that absolutely floods the universe.

Or it could be made of many different things

that all work together to combine to make this effect.

Is dark matter all primordial black holes?

Is it something else that we haven't thought of yet?

Gravitational waves could provide those answers.

The detection of tiny gravitational waves

generated by primordial black holes

will be a huge advance in our understanding of dark matter.

With gravitational wave astronomy, we're seeing things

that we have never seen before.

So, who knows what we're gonna see

as we continue to look out into space?

We have been able to see dozens of black holes merge,

two neutron stars merging,

and discovered from that merger

that neutron stars can make platinum and gold.

From thinking that we would never be able to see gravitational waves,

to seeing gravitational wave signals happen on the regular,

it's just crazy.

Already, we've heard epic explosions.

We've identified the brightest lights in the cosmos.

And we have solved some of the biggest mysteries in astronomy.

But that is just the beginning.

MICHELLE: Right now is a golden age in astronomy.

Think of the time that you're living in,

the first detection of gravitational waves by LIGO was only a couple of years ago.

You were here at the birth

of this entirely new view of the universe.

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