Translator: Trina Orsic Reviewer: Sebastian Betti
There are two types of waves
which bring us information about the universe:
electromagnetic waves, such as, for example light,
and gravitational waves.
These are now the new messengers of the universe,
which, with properties completely distinct from those of light,
are opening a new portal for us to explore the cosmos.
Perhaps, we can even discover fantastic things,
incredible things.
Over 400 years ago,
Galileo marked the beginning of a new era in astronomy.
With his rudimentary telescope pointing to the sky,
he discovered the four largest moons of Jupiter.
He did this alone,
although it was based on the techniques of others.
We, the scientists of LIGO,
began a new era in astronomy
on September 14, 2015,
with the first observation of a gravitational wave.
This was possible thanks to these instruments,
to these observatories of gravitational waves
by Interferometer Laser,
optical instruments more sophisticated and more accurate
than ever built before by humans.
These have an L-shape
with arms several kilometers long
and are capable of measuring perturbations of space-time
below one-ten-thousandth of the width of protons.
This thanks to hundreds of scientists
who were working together during various decades.
And also thanks the fact that in a galaxy far away there were two black holes
which had been dancing around each another for millions of years.
But this dance was about to come to its end.
These two black holes fused and merged into one.
In this instant they emitted a large quantity of energy
in the form of gravitational waves.
And this wavefront was traveling for 1.3 billion years
until the day when it arrived to Earth.
And the Earth vibrated.
As it had done many times before and many times after.
But with the difference that, for the first time,
these instruments LIGO had sufficient sensitivity
to be able to detect these waves.
This occurred exactly
a century after Professor Albert Einstein
presented his theory of relativity,
a new theory of gravitation.
It is extremely beautiful and at the same time very complex.
It predicts strange things like black holes and gravitational waves.
Curiously, Einstein
thought that black holes wouldn’t exist or don’t exist in nature
and much less that these waves could ever be detected.
Well this time, Einstein was mistaken.
Today no one doubts the existence of black holes.
We know that supermassive black holes exist
in the middle of almost all galaxies, including ours.
And the first observation of a gravitational wave
merited the Nobel Prize in Physics in 2017.
But this huge accomplishment was not only thanks to the work
of these three Nobel Prize recipients
but rather thanks to the collective work of more than 1300 scientists
spanning over 20 countries
which form the Collaboration LIGO to which I belong.
Because today,
the big advances in science are not accomplished by one person
but rather are the result of this collaborative work,
normally at the core of big collaborations
capable of building cathedrals of science
as in LIGO.
Evidently, this marked a milestone in the history of science
and gave me and my group much visibility.
We received much recognition
and many invitations to events such as this.
According to the theory of general relativity,
gravity is not an ordinary force,
but rather is related with the curvature of space-time.
In some way,
the curvature of space time tells the mass how to move,
and the mass tells space-time how to curve.
When we have mass in movement,
the curvature of space-time must adapt in order to continue.
They produce perturbations,
waves in the fabric of space-time
which travel at the speed of light
and are these gravitational waves.
These waves produce tidal forces on any object they come in contact with.
It’s as if in some way, the fabric of space-time were a net
which expands and contracts when it is acted upon by these waves.
When phenomena are produced
like supernovas or fusions of black holes,
they emit a large quantity of energy in the form of these waves
in all directions.
This causes space-time to vibrate like a drum.
Even when there are catastrophic events,
these waves can be more intense.
The further we move from the source, the more they diminish in intensity,
and when they arrive here on earth, they are extremely weak.
They are so weak, that while practically
any matter or movement can generate many gravitations,
we are only going to be able to measure
gravitational waves sourced from
the most catastrophic and most violent events of the universe,
including the Big Bang itself.
Because with gravitational waves
we will be able to extract information about the universe
when this didn’t even have a second of life.
The challenge for us is not only to detect these minuscule waves,
but also to extract all the information that they contain.
And this could answer innumerable questions.
A few examples could be,
How are black holes formed?
How does matter behave under extreme conditions?
If in fact the theory of general relativity
is the correct theory of gravity?
Or how has the accelerated expansion of the universe occurred?
And I’m not talking about science fiction,
because in reality
there is a global network of these detectors
which are distributed in distinct parts of the planet.
There are already second-generation detectors.
In the United States we have two LIGO observatories
which are instruments of 4 km in length, each of them:
one located in Livingston, Louisiana,
and the other in Hanford, in the state of Washington.
In Europe we have GEO600
which is located in the surrounding area of Hannover in Germany,
and we also have Virgo in Italy, in the area outside of Pisa.
In Japan, there is another instrument, Kagra,
that has arms 3 km in length,
and is the first that is underground in the mines of Kamioka.
All of these observatories had been working together
and have all contributed in making huge discoveries.
And that’s not all,
because LIGO in this moment is building another detector in India
and we are already involved in the design of future detectors
like the Einstein Telescope or even the future space mission LISA.
All this in order to explore the universe thanks to the observation of phenomena
such as fusions of black holes or neutron stars,
neutron stars in rotation, explosions of the type of supernova
or a possible cosmic microwave background
of gravitational waves
that can help us study the primitive universe.
Each one of these phenomena is characterized by distinct signals.
In some way, all of these together
are writing and contributing to the symphony of the universe.
To this day there have been several dozen detectors.
This has permitted, for example,
to describe a new population of black holes
and raise new questions about stellar evolution.
We are not working alone.
We are collaborating with many other observatories.
In August of 2017 we saw the breakthrough
of multi-messenger astronomy and gravitational waves.
And this, thanks to the first detection
of a binary system of neutron stars
which had been observed.
This was a spectacular event,
because apart from gravitational waves,
we could measure or see an explosion of gamma rays
and also a kilanova in which a large quantity of matter
was released after.
This spectacular phenomenon could be observed by all observatories
on Earth as well as in space.
There were many groups from all over the world
who contributed to this study
which gave us a lot of information.
Some examples,
to prove that gravitational waves and light travel at the same velocity,
to relate explosions of gamma rays with fusions of neutron stars,
to study the behavior of the matter inside
and also to measure the Hubble Constant,
the constant expansion of the universe.
And if that weren’t enough,
we could also discover the origin of the majority of heavy elements
which we have here on Earth,
for example all the gold that we have.
As Carl Sagan said, “We are made of stardust.”
Here, my group in the University of the Balearic Islands,
form part of this LIGO Scientific Collaboration,
of GEO, of the space mission LISA
and also of the future Einstein Telescope.
Our work is based on the search of the study of these waves,
stemming from the fusion of black holes
as well as neutron stars.
You can say, we are dedicated to exploring the universe.
But there is a lot behind the scenes, there are people.
There is human capital.
There are young men and women from various countries
who are renovating this field.
All of them work very hard and dedicate a huge part of their life
not only to the investigation but also to transmit this knowledge.
Including in adverse times like this.
In the history of astronomy,
each time there was a new band in the electromagnetic spectrum,
there have been great discoveries.
Now the gravitational waves are these new messengers
which offer us a spectrum completely distinct to that of light,
which has properties completely distinct to those of light,
with which, perhaps, we hope to discover other phenomena
which today I cannot even imagine.
And including, perhaps to revolutionize the actual concepts
that we have of the universe.
The current generation of instruments
has marked for us the beginning of a new era in astronomy.
But curiously these instruments can only observe the tip of the iceberg.
With them we are only exploring a small fragment of the universe.
These gravitational waves are now the new messengers,
because the universe speaks to us.
And now we can listen.
(Applause)