Original subtitles

- [Narrator] We know it's there

and we usually pay it little mind.

Yet, we notice it when it's not there.

Gravity is the all encompassing force

keeping us on the ground

and the planets in their orbits.

In space, we are merely cheating gravity.

Falling just as fast, but missing the ground.

An orbit, a so called condition of microgravity.

Now this fundamental universal force

is slowly giving up its secrets.

(dramatic music)

(light music)

Humans live in a gravity field.

So what happens when they spend extended time

in the zero-G environments?

And how can we utilize what we learn to help human beings?

This A310 zero-G aircraft is being used

by the European Space Agency

for research in conditions of microgravity.

To obtain zero-G, the plane must perform

a series of parabolas.

On each maneuver, people first experience almost two Gs,

feeling twice their normal weight.

When the aircraft reaches a specific point,

they inject the plane into the parabola.

Everyone on board is then in microgravity.

- It's now called out the angle, it's 40 degrees at 50,

injection that is weightlessness.

Here I go.

The scientists have 20 seconds of weightlessness

to do their experiments behind me.

But there will be 30 of these parabolas.

So they have plenty of time, 10 minutes in fact,

to do their experiments.

Time to get down now, 'cause there'll be a nasty thud.

There we go.

- [Narrator] There are 12 experiments on this flight.

Including six by students as part

of ESA's flying thesis program.

The experiments cover everything

from fundamental physics and neuroscience to psychology,

looking at body image and perception.

This experiment is examining the effect of microgravity

on the brain.

That's important for astronauts

doing long-duration stays on the ISS.

But there are also wider applications.

- We are also interested in people with diseases.

For example Alzheimer's disease or dementia.

If we know the mechanisms which are linked

of a reduction of cognitive performance

and brain activity and where that comes from,

we might be able to better design strategies

to then help these people.

- [Narrator] Inside here is a pulsating heat pipe.

Potentially a new way of managing the thermal conditions

of satellites or components on board the ISS.

The copper pipe, seen here showing the flow

of a condensed vapor,

also has a section made of sapphire

that is transparent to visible and infrared radiation.

- In this experiment, we're using the infrared camera

of the European Space Agency.

It's a new camera, high-speed infrared camera,

that will be used also on the International Space Station

for the next experiment.

- [Narrator] After each parabola,

there is another 20 seconds of two G

as the plane pulls out to level flight.

A few minutes later, the next parabola begins.

In between each one, scientists must quickly

reset their experiments and prepare

for the next bout of microgravity.

- This is the only microgravity platform

where the scientists get to interact

with their own experiment while it is in zero gravity.

Rather than doing it by remote

on a robotic capture or sounding rocket.

Or on the ISS it's humans of course,

but then it's astronauts doing it

and they can't possibly be as in tune

with the scientific needs as the scientists themselves.

So this is the only platform

that really allows that kind of access.

And as such it's unique.

- [Narrator] In the final few parabolas,

everyone works hard to finish their science.

For the German Mars Society experiment, however,

there's only one shot to get this right

as it involves testing the initial deployment

of a densely packed balloon

that they hope one day will carry instruments

for studying Mars' atmosphere.

Whether it's preparing for Mars

or helping life on board the space station and on Earth,

the zero-G plane offers a unique environment for research.

And the closest conditions possible to being in space.

Of course the ISS is the ideal place

to experiment with gravity or the lack of it.

Many experiments are conducted by the crew every day.

With new experiments being sent up to the crews

in cargo and crew capsules.

(announcement over speaker)

Fundamental questions are still to be explained.

Most fundamental of all, what is gravity?

How can such a weak force dominate the entire universe?

(electronic music)

How does it keep moons and planets in orbit?

It affects everything, no matter what its mass may be.

A leaf will fall as fast as a handful

of nuts and bolts in vacuum

as tested on the lunar surface

many years earlier by Apollo astronauts.

It was this man who explained the force of gravity

in the space-time continuum early in the 20th century.

He theorized that gravitational waves

were oscillations in the fabric of space-time,

moving at the speed of light,

and caused by the acceleration of massive objects.

- [David] Gravitational waves were predicted by Einstein

almost 100 years ago.

- A gravitational wave is a ripple in the fabric

of space and time

that's produced somewhere in the distant universe

and travels across the universe.

- [David] When any massive object moves,

it's changing the nature of space-time,

that's what Einstein taught us.

- So you have a motion that stretches space in one direction

and compresses space in the other direction.

- Nobody really believed at the time of the prediction

that you could ever detect them,

because the size of the effect was so small.

- [Narrator] It would take multiple, massive detectors

around the world to sense such a small effect

passing through the Earth.

(upbeat music)

(dramatic music)

Question, how do you detect gravitational waves?

Answer, with a Michelson interferometer.

This is the GO 600 in Germany.

Laser light is split and sent

along different paths in a vacuum,

the longer the better.

Then reflected back on mirrors

suspended on glass threads.

Completely isolated from any earthly vibrations.

The laser light is then brought back together

and the interference patterns of the two beams compared.

The sensitivity required is astounding.

- We literally look for changes

in the space-time distance in our instruments

as the gravitational wave goes by.

- And the gravitational wave pushes them together and apart.

By one 1,000th the diameter of the nucleus of an atom.

No wonder its taken so long to pull this off.

- [Narrator] The first detection was made by LIGO,

two detectors a continent apart.

- We have observed gravitational waves

from two black holes forming a larger black hole.

- They're moving at the velocity of light.

Damn near it, that velocity.

30 solar masses moving that fast,

I mean they're putting out incredible amounts of energy.

- [Kip] And when they collide with one another

they produce a bigger black hole.

But they also produce gravitational waves.

And in that process, about three solar masses

just disappears and goes into gravitational waves.

- [Narrator] September 2015 confirmed

Einstein's vision of the waves

and allowed a fascinating and unique view

into the dark side of the cosmos,

creating a new science, gravitational wave astronomy.

Gravitational waves carry information

that you can't obtain any other way.

Massive events like a supernova,

two neutron stars colliding,

even the universe-creating Big Bang itself

have all produced gravitational waves.

These can now be detected, adding pieces

to the jigsaw picture of nature

and the forces that define space-time.

Barely two years later,

another scientific milestone was reached.

Astronomers using a fleet of ESO telescopes

have observed a visible counterpart

to gravitational waves for the first time,

a kilonova from merging neutron stars.

(dramatic music)

August 2017, the LIGO facilities

in collaboration with their European counterpart, Virgo,

together detected gravitational waves

rippling through the fabric of space-time.

Just two seconds later,

two space telescopes from ESA and NASA

detected a short gamma ray burst

coming from the same general area of the sky.

This coincidence had never been seen before.

Astronomers hope this was not just a coincidence,

but another indicator of this cataclysmic event.

Two neutron stars combining in an explosive merger.

If scientists were right,

then a visible light counterpart

known as a kilonova would be expected to follow,

revealing the exact location of the source

of gravitational and gamma rays.

The hunt was on.

ESO and ESO partner telescopes in Chile

joined other observatories to search

for a new light source.

They were looking for a needle in a hay stack,

a faint new glimmer amid millions of stars.

But amazingly, they found it just a few hours later

in the galaxy NCG 4993, 130 million light years from Earth.

(dramatic music)

Neutron star mergers are the furnaces

where most of the chemical elements

heavier than iron are forged.

The kilonova, an event 1,000 times brighter

than a typical nova,

spreads the newly formed elements

including gold, platinum, and uranium,

into the surrounding space.

(dramatic music)

Such an explosion had never been confirmed before.

But here was one that could be studied in great detail.

The ESO observations revealed an extraordinary

and rapidly changing event, closely mirroring theory.

(dramatic music)

Heavy, radioactive elements were shot into space

at one fifth the speed of light.

In just a matter of days,

the kilonova's color changed rapidly from blue to red,

faster than any other observed stellar explosion.

(dramatic music)

This event marks the start of a new era

of multi-messenger astronomy.

For the first time in history,

we can now combine light signals

with gravitational waves,

providing a totally new way to probe the universe.

(upbeat music)

(light music)

The advancement of gravitational wave detection

didn't stop there.

Talented engineers and scientists

set about developing even more sensitive detectors

that could be mounted in space

free of nagging, earthy vibrations

and detector size limitations.

(countdown in French)

A proof of concept mission,

laser interferometer space antenna, or LISA pathfinder,

was launched to test the feasibility

of a space-based gravity detector.

(bright music)

LISA pathfinder was launched from Kourou, French Guiana

aboard a Vega launcher into a slightly elliptical

parking orbit.

(bright music)

Using its own propulsion module,

it progressively expanded its Earth orbit

over a period of two weeks

before the cruise phase to its operational orbit,

the first Sun-Earth like Lagrange point L1.

One and a half kilometers from Earth towards the Sun.

(bright music)

The science package was built

around two, identical, gold and platinum cubes,

each floating free in a vacuum.

They act both as mirrors for the interferometer

and as inertia references for the drag-free control system.

A disturbance reduction system, or DRS,

was supplied by NASA and consisted

of two clusters of colloidal micro-propulsion thrusters

and an electronic unit containing a computer,

with associated drag-free control software.

- So to me the highlight of LISA pathfinder

is the very first day we turned her on.

Because we didn't expect the performance to be as good.

We thought we would be close to what we had to do

and then we would improve it.

We would think about what we have to do,

we'd fix things, and we'd get better.

On day number one it met requirements.

And what it showed us is that this

is a very complex type of instrument but it's doable.

And industry now have the experience

and know how to make a machine like LISA

and LISA pathfinder.

- These signals are very, very tiny indeed.

And we've been able to show with these test masses

inside the LISA pathfinder satellite

that we would be able to see gravitational waves

in the frequency band where we're interested in.

- I think LISA pathfinder is already

the most treated that is possible actually.

To place two test masses free-fall in space

is with residual relative acceleration

at the level required

for the future gravitational wave detector.

(people murmuring)

- [Narrator] LISA pathfinder confirmed the technology

for a space-based gravitational wave detector

even before the science operations began.

- So a space-based detector like LISA

is looking for low-frequency gravitational waves.

And by low-frequency, really we're talking

about very big objects which are in motion.

So we're looking at the centers of galaxies,

the super massive black holes

at the center of a galaxy.

And when two galaxies merge,

the two black holes eventually form one big entity.

And it's in that merging of the two black holes

is what we're picking up through LISA.

- [Narrator] Proving this type of technology in situ

is a big leap forward in detectors.

- It has worked flawlessly

and her performance is better

than we could ever have dreamt.

Even on the very first day we had met our requirements

and since then we've just made it better.

And it's just wonderful to see

how well this instrument is performing.

The success of LISA pathfinder demonstrates

that we now know how to build a mission like LISA

and over the next months and years,

that mission will now start to be in the design phase

leading to a launch in the late 2020s or 2030s.

(upbeat music)

(electronic music)

Gravity is the fundamental force of the universe.

At the largest scales,

I'm talking about stars, galaxies, the universe,

they're dominated by gravity.

However, gravity does not get absorbed

very well by matter.

We're sitting here in a building,

we're not floating off in space,

we've got a building between us and the air.

So gravity penetrates all matter.

So, for that reason the gravity

is passing through our detector

and it doesn't really dump any energy

in the detector that we, an electromagnetic telescope,

would pick up light.

So we have to actually look at the ripples in space-time.

We have to look at the effect of gravity over all of space.

- [Narrator] And like other waves propagating through space,

gravity waves, too, have various wavelengths or frequencies.

- We need LISA because it's looking

at a whole new part of the spectrum of gravitational waves.

It's a whole new type of science we're doing.

So with the LIGO detections

they're looking at objects roughly the size of the Sun

so anywhere from one to 100 times the mass of the Sun.

And in their case it was about 30 solar mass black holes

which were orbiting each other.

Whereas with LISA, we're looking at galaxies merging.

Which is no longer stellar light objects,

it's now galactic objects.

So things which are maybe a million times

the mass of the Sun.

The big black hole at the center of galaxies

when galaxies merge together,

events of these black holes collide.

And when that happens it rips the universe apart.

And we're looking for that universe vibrating

from these mergers, these big, big events.

Something you could never, ever do that on the ground.

So LIGO will never be able to see events we see with LISA.

(electronic music)

- [Narrator] The LISA mission

will consist of three satellites,

precisely positioned to each other

in an Earth-trailing orbit.

There, they will connect to each other via laser beams

forming a single detector.

(electronic music)

- [Paul] So the big difference between LISA

and LISA pathfinder is the length of the arc.

So in LISA pathfinder we had two, gold-platinum cubes

in our space craft,

and were separated by about 40 centimeters.

Whereas in LISA, the little cubes

are separated by two and a half million kilometers.

So to put that in perspective,

that's about six times the distance to the moon.

So that is a long, long way.

(electronic music)

- [Narrator] Work has begun on the LISA project.

It will take over a decade to plan, design and build,

and test the three space craft.

When LISA launches in 2034,

it will be able to detect gravitational waves

from objects up to 100 times the mass of our Sun.

The engineering challenges alone are daunting.

- So the challenges of a mission like LISA

or LISA pathfinder is the fact that it's built

with I think we had 40 different companies

from 14 different countries building aspects.

And unlike some of the planetary missions,

some of those early missions,

where you have a camera and a telescope,

our whole satellite is one instrument.

And if we go to LISA, all three satellites

form one instrument.

So everything has to come together,

it has to work, and that's what happened.

You know, with our very great collaboration within Europe.

And when it all came together,

it worked as an instrument on day one.

(electronic music)

- [Narrator] But none of that would've been possible

without Albert Einstein, LIGO, and the LISA pathfinder.

Its success has paved the way

for a whole new window into the mysteries of our universe.

(dramatic music)

- Gravitational waves allow us to see

the dark side of the universe.

The things which are not shining light,

for example, black holes.

So now we can actually go out there

and we can really observe these things

which we've got no other way to see.

And also the gravitational waves

were predicted by Einstein.

And this is one of the main pillars of general relativity.

And with LIGO, and even better with LISA,

we can really start to probe general relativity

and see if that is actually theory

which governs the gravity of the universe.

(dramatic music)