Gravitational waves: the long journey of science | Gabriela González | TEDxCórdoba

Gabriela is a renowned scientist from Córdoba. She proposes to reflect on what was most asked during the last year following the discovery of gravitational waves: what is science good for?

Gabriela has a B.Sc. in physics from the National University of Córdoba (Argentina) and a Ph.D. from Syracuse University (USA). Nowadays, she is a professor at the Louisiana State University, where, together with her research group, she is dedicated to the calibration, characterization and data analysis of the gravitational waves detectors in the states of Louisiana and Washington (USA). She is the elected spokeswoman of the LIGO scientific collaboration project (Laser Interferometer Gravitational waves Observatory), and she was part of the scientific team that announced to the world the discovery of gravitational waves in February 2016. This work, led by Gabriela and carried out by a team of more than a 1000 scientists from 15 countries, corroborates propositions of the theory of relativity enunciated by Einstein a century ago. From that moment on she has achieved great international recognition, and the journal "Nature" has named her one of the 10 most influential scientists of 2016.

This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Learn more at http://ted.com/tedx

1,300 million years ago,

there were two huge black holes
that were dancing tango.

They were, while dancing,
forming waves in space-time,

deformations of space-time.

And they were getting closer and closer,
turning faster and faster,

almost at the speed of light,

until, embracing each other,
they formed a single black hole,

60 times the mass of our Sun,

with a radius of 200 km.

And gravitational waves
took the message of that embrace,

at the speed of light,
to the rest of the Universe.

This, sounding like science fiction,
a Hollywood movie, was true.

And we know it was true

because we measured
those gravitational waves,

last year in 2015.

The story of this discovery
is also pretty long.

When this event happened
1,300 millions years ago

in a faraway galaxy,

on Earth, the first multicellular
organisms were just appearing.

Life, humanity, societies grew, advanced,

and a little over 100 years ago,

in 1915,

Einstein published his
theory of general relativity.

It's a theory of gravity.

Relativity and gravity don't sound like
the same thing, but they are.

His theory says that two masses
attract each other,

two black holes,
or the Earth and the Sun,

attract each other, not because,
as we're taught at school,

there's a gravitational force,

but because all masses,
according to this theory,

deform space-time,

just as we do when
we lie down on a mattress.

When we, a physical mass,
lie down on a bed,

we deform the mattress,
making a depression.

And if someone else lies down on the bed,
they will roll closer to us.

That is the force of gravity
as Einstein imagined.

The Sun deforms space-time.

The Earth does not feel
an instant gravitational force,

but it sees the space-time curvature,

and the Earth spins around the Sun
as we know it to do.

What is space-time?

We have to imagine space-time as a grid,

not a two dimensional grid,
but a three dimensional one,

the three spatial dimensions
that we can measure with rulers,

with time, with clocks.

A grid of rulers and clocks.

Four dimensions,
and all of them are connected.

That is the space-time that gets deformed
according to Einstein's theory.

The theory is pretty complicated,

but what matters with theories
are the predictions they make,

and the checking of those predictions

to prove them right or wrong
experimentally,

so as to know whether to believe
the theory or not.

And Einstein's theory
makes many predictions,

all of them very crazy,

quite incredible.

One, for example,

the first to be verified
a few years later in 1919,

is that light does not travel
in a straight line

but deflects when it passes
close to a mass,

it deflects a little bit,
by a certain amount.

And that was verified in 1919,

and the theory
was rather better believed.

But it also made other predictions.

For example, it being
a theory of space and time,

that clocks are not always synchronized.

If we start, me and you,

with atomic clocks synchronized
to the millionth of a second here,

but then you go and hike up the Aconcagua,

our clocks will no longer be synchronized.

Yours will be always ahead of mine.

And why is that?

It's because space-time is dynamic,

and your clock is further
from the Earth than mine.

Distances and gravity change time too.

Another prediction was
this prediction of gravitational waves.

Since masses distort space-time,

and masses are moving,

those little ripples in space-time
are also moving,

and they are traveling
at the speed of light.

And what they do, is to take distances
and stretch and shrink them,

stretch and shrink them,
in proportion to distance.

But when Einstein,

or any of the other scientists
that followed him,

calculated how much
the distances distorted,

it was very, very little.

He even wrote that this would
probably never be measured.

And many people thought he was right,

that this was one of those predictions
that cannot be measured.

As I said, it is a long story.

In the 70s, people thought that
it indeed could be measured.

There are some instruments

that are widely used
in physics and engineering

to measure distances very precisely,

which are called interferometers.

Interferometers because they use light,
and the interference of light.

We take a ray of light,

split it in two
with a half-silvered mirror,

reflect them back with mirrors,

and when the two rays
arrive back, they interfere.

The waves interfere destructively,

they destroy each other,
and there is no resulting light,

if this distance
and this distance are the same.

But if this distance gets shorter
and this one gets longer,

or the other way round,

then the interference out here
is not totally destructive,

and we can see a little light, or not.

So, by measuring with a photodetector
how much resulting light there is,

we can measure the difference in distance
between this distance and that distance.

It looks simple enough
to measure distances,

and it is used a lot,

but what's the amount we have to measure?

That is the big question.

The theory predicts that,
resulting from these black holes,

the distance between
the Earth and the Sun

changed by an atomic diameter.

And all smaller distances
by less than that.

But those scientists in the 70s,
starting with scientists at MIT,

said this can be measured.

If we construct interferometers 4 km long

in a vacuum with hanging mirrors,

we could get to measure differences
between this 4 km and that 4 km

of a millionth of a proton.

Many laughed; others didn't.

Many other people
started believing this.

The national science agency
of the United States

bet on this in the 90s.

From the 70s to the 90s,

when these interferometers
began to be constructed,

two interferometers, two LIGOs,

one in the state of Washington,

and one in the state of Louisiana -
quite close to where I live -

3,000 km apart.

They were completed in the 2000s.

First generation technology
was operated and it went well.

It didn't discover gravitational waves,

but it was known that the technology
had to be made more advanced.

In 2010, the second generation
of this technology began to be installed.

It worked.

It works - more or less.

In 2015, we said that we should start
taking a look at what is happening,

in spite of needing
to do more work on the detectors.

In 2015, we started collecting data
with these two detectors.

And in September,

on September 14th, 2015,

these photodetectors told us

that, 3,000 km away, we had signals
indicating this gravitational wave.

We couldn't believe it.

And in December it happened again.

Listen.

(Sounds)

That sound seemed impressive to us.

We marveled.

It left us speechless
and dancing afterwards.

This is the sound of the Universe.

This is the music of the Universe.

We felt that from that moment -

Before that we were looking
at the Universe

with electromagnetic waves
and telescopes and observatories,

and now we were listening to it,

with gravitational waves.

We had added another sense.

And from then on,

we have not only been working
to measure more gravitational waves,

but we have also been talking about this.

And many people ask me:

"And what are gravitational
waves good for?"

And I say, "And what are
gravitational waves good for?

What is astrophysics good for?
What is science good for?"

Ah, that we know. We all know
what science is good for.

All the technological advances
that we use in communication,

in transport, in medicine,
all that is based on science,

we all know.

But gravitational waves, astrophysics?

Actually the path
science takes, is very long.

It starts with basic theories
relating to how the Universe works,

and then, they are applied.

First they test to see
if the theories are good or bad.

After that, ways in which
they can be applied are discovered,

in general, in other areas
of physics or chemistry.

Engineers take hold of it all
to build precision instruments.

And finally, sometimes,
new useful technologies appear.

If Einstein had been asked in 1915:
"What is your theory good for, sir?"

He would have said:
"To better understand the Universe,

to explain gravity.

What else does a theory
need to be good for?"

Yet, today, many of you
are going to use the theory of relativity

when leaving here

if you are going somewhere you don't know.

Because GPS needs
the theory of relativity.

It needs many other things,

but if it doesn't take into account
that the clocks in the GPS satellites

and ours, our clock, our little device,

are desynchronized

because they are
at different distances from Earth,

the GPS will lead us to the wrong place.

And I, that uses it all the time,
would get lost.

So the theory of relativity,
almost 100 years later,

has practical applications.

And so it is with everything.

Science takes a lot of time

in producing useful
applications and technologies,

and many people working
with many different abilities.

If we think what technologies
we wouldn't have today,

what wouldn't have been invented

if basic effects in physics,
in chemistry, in mathematics,

had not been studied a 100 years ago,

there would be a lot of technologies
that would not exist today.

The laser, GPS, medicines,
medical applications.

A whole load of technologies.

The challenge I put to you

is to imagine

when you hear about a discovery
like the one of gravitational waves

or any other discovery in astronomy,
in physics, in mathematics,

that show up in the newspapers
many times a year,

when you hear about those discoveries,

what technologies
will there be in a 100 years

that will use these theories?

That is the challenge for you.

Thank you.

(Applause)