- Thank you to Draper and its Hack The Moon initiative
for supporting PBS Digital Studios.
Here's a ridiculous idea,
imagine I snapped a twig in an isolated forest,
then a listener on the opposite side of the planet
hears the sound vibrations created by the snap,
and just by hearing it, can tell you exactly where I was,
at what time I snapped it,
and even what kind of tree the twig came from.
Of course, this is impossible,
but what if I told you
that human beings could do something similar,
but even more impressive.
Instead of a snapped twig,
the source of the vibration is a violent event in space,
an event that we can detect here on Earth,
even though it occurred billions of light years away
and billions of years in the past.
All we had to do was build
one of the largest and most sensitive devices ever created,
the Laser Interferometer Gravitational Wave Observatory,
LIGO.
(ethereal music)
I'm driving alongside
one of the four kilometer long arms of LIGO,
the first ever observatory to observe gravitational waves.
The arm is so long that they actually had to correct
for the curvature of the earth,
and we're about to go inside to the facility
to see all the instrumentation.
I am so excited.
We're getting on some of our clean room garb.
This is a Class 10,000 clean room.
There's more classes, but this is pretty clean.
Oh, yes.
Yeah, this is cool.
So, this is like, laser starts over there,
Then there's mirrors here, beam splitter, laser splits.
We've got the arm going this way,
another arm going that way.
- It's all in this room.
- So, this is like the brain, the guts,
the like, this is everything. - Yes.
- Up until extremely recently,
astronomy was based almost exclusively on studying light,
but LIGO is not like other observatories, it's blind.
It senses no part of the electromagnetic spectrum,
like visible light, microwaves, radio waves,
instead, it detects gravitational waves,
which are a completely separate phenomenon from light.
In 1916,
when Albert Einstein published
his Theory of General Relativity,
he predicted that masses accelerating in space
would create ripples in the fabric of space time itself.
For decades,
no one knew if these ripples, called gravitational waves,
actually existed, but 99 years later, in 2015,
the LIGO team finally sensed a series
of extremely tiny vibrations,
1/1,000 the width of the proton.
To get to that level of sensitivity,
they needed to create an observatory
that was unlike anything else on earth.
Rather than pointing a mirrored sensor at the stars,
they built this L-shaped detector
with two, four kilometer long vacuum tubes.
The arms are covered in concrete,
so they're completely protected from all the elements.
Then they use lasers and mirrors
to detect the compression of gravity
with special suspensions that actively cancel out
any vibrations generated from activity on the earth,
and they needed to build two of them 3,000 kilometers apart
to operate in complete coordination,
because a random vibration at one location
could create a false signal
that looks like a gravitational wave, but isn't.
If a detection is made at both places,
you eliminate the possibility
of it just being a local disturbance.
- [Amber] The beam splitter itself,
is in this large chamber right here.
- [Dianne] Oh cool.
- But part of the reason why that's so large as well
is not just the mirror,
but you've got it in that quad suspension system,
and that quad suspension system is really where the magic is
in reducing the ground vibrations.
Because if you don't reduce those ground vibrations,
you don't make detections.
- And you have that quad suspension system on?
- On the four main mirrors, as well as the beam splitter,
so the five largest optics that we have
that is in those suspension systems.
We really say every vibration bothers us, and we mean it.
From the thermal effects on the mirrors
to earthquakes in Australia, they all can cause us problems.
- After months of analysis,
scientists confirmed that the vibrations detected in 2015
were the signature of two black holes merging.
It was a violent event
that had occurred 1.3 billion light years away
and 1.3 billion years in the past.
It also confirmed
that an entirely new type of astronomy was possible.
Wow, so this is it.
- Those are where the lasers exit the enclosure area
and go directly into the vacuum system.
- Wow.
There are laser beams going through these tubes.
- [Amber] Yes.
- That is very exciting.
They're in infrared though,
so we would not even be able to see them,
if there were no protective tubes there, but still.
There's this laser beam that comes out, and it's got,
it's a bit messy, it's got different,
it's different sort of spatial patterns,
and they clean it before it gets sent out into the arms.
But then, you're telling me now,
that they also clean the input that comes back in,
or the output is what you call it.
- Yeah, absolutely,
so you're getting rid of the patterns
of light you don't want. - [Dianne] Right.
- And then, you do that before it goes in,
and you also do that on the way back out.
So yeah, the light comes back in, recombines,
and then it goes down here for detection.
- And then, detection happens over here.
So this like this part that we're gonna walk up to,
this is where the detection happened?
- Yeah.
I hate to say where the magic happened,
because the magic happens all over,
but this is where the actual detections are made.
- This is amazing.
You've got to see this.
(both laughs)
The beam makes it here where you've got the detector,
that's where the detection happens.
- And, I actually have the photo diode in my office
that solved the first gravitational wave ever, GW 150914.
- How did you get that?
- Well, 'cause I have to put it out.
- Okay.
We're putting goggles on
to protect from the infrared laser,
which you wouldn't be able to see,
but you would be able to feel it.
LIGO is allowing researchers
to explore areas of the universe that were previously hidden
because their energy is emitted
by objects that are inherently dark,
like the collision of black holes.
We now know that over millions of pairs of black holes
revolve around each other in binary systems.
As they orbit, these pairs emit gravitational waves,
which remove some of the system's energy
and forces the pair to rotate faster and closer together.
But because this energy isn't released as light,
prior to the detection of gravitational waves,
we were never able to observe them,
and the very existence of such black hole binaries
was contested.
But perhaps,
the most exciting use of gravitational wave detection
is yet to come.
In the very first moments of the universe,
the electromagnetic force and the weak nuclear force,
two of the fundamental forces of the universe,
were indistinguishable.
But when those forces separated,
they're believed to have produced gravitational waves,
and unlike light waves,
gravitational waves interact extremely weakly with matter,
so much so that gravitational waves could still be traveling
from a time when the universe was a billionth of a billionth
of a billionth of a billionth of a second old.
If we can build a detector
with enough sensitivity to observe these waves,
they might give us some information
about the very first moments of our universe,
which is very exciting.
And while this degree of accuracy might be far off,
the stunning success of LIGO so far
has empowered the advancement
of bigger, more sensitive gravitational wave detectors
around the world and even in space.
Ultimately,
gravitational waves tell us how stars live and die.
They give us insight
into the lifespan of ravenous black holes,
and they may reveal
what happened at the very beginning of time.
Gravitational waves are a profound expansion
of our human senses, broadening our vision,
and bringing us one step closer
to understanding the inner workings of the universe.
Now that you know all about gravitational waves,
keep watching as Joe Hanson explores
how scientists created
humanity's first image of a black hole
with a telescope the size of the earth.
Thank you to Draper and its Hack the Moon initiative
for supporting PBS Digital Studios.
You know the story
of the astronauts who landed on the moon.
Now, you can log onto wehackthemoon.com
to discover the story of the male and female engineers
who guided them there and back, safely.
Hack the Moon chronicles the engineers and technologies
behind the Apollo missions.
Brought to you by Draper,
the site is full of images, videos,
and stories about the people who hacked the moon.
PBS is bringing you the universe with the Summer of Space,
which includes six incredible new science and history shows
airing on PBS
and streaming on pbs.org and the PBS video app.
Watch it all on pbs.org/summerofspace.