Translator: Michele Gianella Reviewer: Federico MINELLE
I'll tell you a story
that started 1,2 billion years ago.
More or less.
It's a love story,
With a quite unusual couple: they are two black holes.
For millions and millions years,
they spin around each others, slowly getting closer and closer.
For millions and millions of years.
Even among black holes, love is complicated!
At a certain moment,
they were so close that they collided
and merged in a single black hole.
That generated a huge gravitational wave,
which traveled across space and time for countless years and kilometers,
and last September it got here, on Earth,
and we saw it!
Then, after months and months of analysis, statistics,
and whatnot - and poor sleep also -,
we announced to the whole world
we have seen the first gravitational wave.
This story could finish now,
but I bet you have a lot of questions now.
Like, what the hell is this guy talking about?
What are these gravitational waves?
Time for some history.
Let's come back to 100 years ago,
when a man you probably heard about already,
he was called Einstein, if I remind well,
wrote a paper about something he called relativity.
He said a lot of crazy things:
moving clocks run slower than still ones;
motion shrinks objects;
space and time interact among each other.
Amazing!
And he didn't stop:
ten years later, he also said
that each mass affects the space around it.
This is really crazy.
And as I already said,
one year later he introduced gravitational waves.
But what does it mean that mass warps space?
Imagine that space is like an elastic surface.
If you walk on it,
you just go straight, and it is done.
But if you put something on the surface,
it gets distorted,
and you have to walk around this warp.
So, for instance, the Sun warps the surface around,
e we let the Earth run around it.
What happens?
Earth follows this warp,
like when there's a vortex in the sea,
and ships follow the vortex and cannot escape.
Let's go on a bit, now.
Ok, let's take mass in movement on the surface.
If these masses move, the surface also moves,
and what are the consequences?
That not only near masses move,
but also those far away.
If we drop a stone in the water, what happens?
Waves propagate far away.
So this surface that continuosly moves
far away from the masses, these are gravitational waves.
Now we know what they are.
What do they do?
When a gravitational wave comes to Earth,
it happens what you see in this movie.
That's scaring, isn't it?
So, why on September 14th you did not see this?
Why you do not see your friends moving like this?
When a gravitational wave arrives,
distances are squeezed and stirred.
But they shake very, very little.
We are speaking of distance less than a nucleus of an atom,
we cannot see it with our eyes.
So, how can we detect a gravitational wave?
In the 60s,
scientists developed resonant detectors, made with aluminium bars.
They tried to see if these bars were enlarging.
The idea was good... but it didn't work very well.
So, some years later, they built these so-called interferometers.
What are interferometers?
We take lasers, because lasers are always
And what do we do?
We shoot a laser beam and let it run on two different directions.
The laser beams travel the same distance,
and when they come back to the starting point,
they sum and cancel,
so we don't see anything.
But if a gravitational wave passes by,
the two distances traveled by the lasers beams are different,
they no longer annihilate like before,
and we see some light.
Looking at this light, we see the waves.
So, we essentially understand how to see these waves,
but what can we do with them?
Now our friend Fido, behind me,
invites you to play a game.
At my signal, substantially
close your ears for some seconds.
I raise my hand,
so when I'll put it down, you can restart to hear.
Ready? Understood? OK?
3-2-1, Go!
Good, very good.
A second game now, our friend likes to play.
Now you close your eyes,
and my voice will tell you when to open them back again.
Ready? 3-2-1 Go!
Now relax.
You are in the park,
birds are chirping.
There's also a gentle breeze.
Your boyfriend, or girlfriend brought a picnic.
Ready to eat?
Go ahead.
OK, you can open your eyes.
What did we do with these games?
When we close our ears,
that's how we looked at the Universe so far:
with light, with eyes.
This is the light visible spectrum,
but you can see that there are holes, it's called absorption spectrum.
Why?
Because when light travels in our atmosphere,
it meets hydrogen, helium, nitrogen, and whatever is there.
Hydrogen takes something from the light, so does helium,
nitrogen another piece, and we have holes.
Let's do one example:
it is like sending a mail to a friend of yours,
and the postman delete some words.
What a bastard...
You can read the mail, of course, but you lost some words.
Same thing with light.
Gravitational waves envelopes are so tough,
that no postman can open them.
But there is more to it.
When you used only eyes,
you could just see a stupid man on the teather with a hand up.
But when you listened to me, probably someone of you
really felt to be in that park.
Gravitational waves
are a new messenger to describe the Universe.
We have already a lot of them: visible light, infrared light, gamma rays,
and everyone gives new, different information.
So even gravitational waves are in a sense our way
to hear the Universe, not just see it.
So do they give us new information.
Really? Yes!
Take black holes, for instance.
For the first time
we really heard black holes speaking.
Up to now, we cannot see, because they are black.
Nothing can exit from a black hole.
But gravitational waves from black holes arrive to us.
And we saw it.
Should we stop here?
We can, but we want more.
There's more than black holes in the Universe.
Neutron stars are also there, for instance.
Neutron stars are objects
more complicated than black holes:
the equation of state, the internal processes...
Then light coming from neutron stars
gives a lot of information, but we don't know everything.
We can learn more from gravitational waves
coming from neutron stars, when we will see them.
Something more?
Why not? Supernovae!
Super novae are huge explosions happening in the Universe,
that make light, neutrinos, gamma rays and infrared light,
and gravitational waves.
They're another messenger that can describe
how these explosion could happen.
And last but not least, the Big Bang.
We know very little about it,
basically nothing!
From its gravitational waves, however,
we could discover the first moment of Universe's life.
Those moments we don't know yet.
So what do we do now? Let's play!
Now really we can detect gravitational waves.
We can play with them.
We can go back to their generation process.
And we can learn something more about how love works in the Universe.
(Applause)