Translator: Guy Petrucci Reviewer: Cesar Augusto Zanin
This is Julia.
Julia is four and a half years old and like all children that age
spends her time observing things around her and asking herself,
"How is this made? How does it work? And above all, why does it work this way?"
The other day Julia put a glass of water in front of me and asked:
"Dad, what is this glass of water made of?"
As a profession I do particle physics
and so I didn't hesitate a second to respond,
"Well, that glass of water is made of three million billion billion
water molecules,"
with a very easy little calculation
that all high school students are capable of doing.
Of course the response didn't satisfy her at all.
"What's a water molecule?" she asked me.
To which I made this drawing, I said to her,
"A water molecule is a chemical compound
made of one oxygen atom and two hydrogen atoms."
"What's an atom?" she asked me at that point.
"Well, an atom is the smallest part of a chemical element made of a nucleus
around which some particles that we call electrons buzz."
And her again, "What's a nucleus? What are electrons?"
And I realized that I would not get away easily.
I noticed on the ground, on the floor of the living room, like in all houses
where there are kids of that age, a pile of Legos spread out,
and so I started to explain to her,
"Look, everything that surrounds us - and when I say everything,
I really mean me, you, mom, the glass of water, flowers, stars -
is made of a very limited number
of tiny little bricks that we call particles."
I started to pick up the little Lego pieces and line them up on the table.
Out of them came a diagram of this sort:
all of the matter that surrounds us is made of twelve particles of two types
which we call leptons and quarks,
but also divided into three families of four
that you see lined up in columns, underneath the big yellow pieces.
And these particles speak to each other by exchanging other particles -
they are like messengers, or some zoo keepers, if you will.
The one that everyone knows is the photon, the red little brick,
the speck of light, the messenger of electromagnetic interaction.
But there are others.
For example, gluons, the transparent brick,
which glue together the quarks inside the atoms' nuclei.
And two others, the green little bricks: the W boson and Z boson.
They are the particles for which Carlo Rubbia won the Nobel Prize in 1984,
which carry the weak interaction.
So you see, you can get started playing
with these particles, a bit like with Legos,
and for example you can put together two up quarks and a down quark
- physicists always give bizarre names to particles -
two blue bricks and one light blue,
glue them with some gluons and make a proton.
Or two down quarks and one up quark and make a neutron.
Now with a proton and a neutron you can make in various amounts
all of the atomic nuclei possible.
For example, in the simplest way, you can take a proton and put
an electron there buzzing around,
held with a lasso by the photon of the electromagnetic field, and voilà,
you've made a hydrogen atom -
one of those atoms that was in the water molecule that we saw earlier.
And the W and Z bosons are kind of like the wizards of the group,
they're the ones that are allowed to transform one particle into another -
for example: an up quark into a down quark or vice versa.
A neutron into a proton, therefore
emitting electrons and neutrons at the same time -
a reaction that may seem exotic and perhaps useless,
but thanks to which our sun shines.
Julia always puts a lot of time into cleaning up her toys.
The Legos often remain spread out on the living room carpet.
Then she looked at this diagram which is so precise, so ordered and asked me,
"How much time did you guys spend making this whole arrangement?"
Really it took a while, if you think that the first block discovered,
the electron, was discovered in 1897 by Mr. Thomson in England,
and to find the last little piece it took over 100 years.
The Tau neutrino was discovered in 2000 by the DONUT collaboration,
which in English means donut
- not because they ate so many of them but because the experiment resembled one -
more than a hundred years later in order to complete the picture.
So Julia looked at me with a bit of a perplexed look on her face and said,
"But if you've put everything in order,
if you understand so well how the little pieces put themselves together
and assemble everything that surrounds us,
then what do you do for work, dad?" (Laughter)
And it's actually a reasonable question because one could
be led to think that this wonderful diagram,
which we usually call amongst ourselves the standard model,
can truly explain everything.
And it does, in a lot of ways.
But it also oozes questions, of why - that go unanswered.
So usually we don't draw it on blackboards in brick form,
usually we draw it in equation form.
I've taken the simplest one for you because it's Saturday morning.
This equation basically describes what I've told you about now
and it works very well.
But it has a bunch of defects.
To point one out, it describes particles as if they didn't have mass.
But we know particles have a mass, it's one thing that we measure.
And so? Where's the problem?
Well, this is a typical case
that explains to us how physics tries to resolve problems.
Why do particles have mass?
Why does a W boson or a Z boson weigh 80 or 90 times more than a proton
when our equation treats them as if they don't have mass at all?
One of us set out on a blackboard, this man for example,
whose name is Peter Higgs, and in 1964 thought that he could add
a piece to the equation that I showed you, that piece drawn in orange,
which I don't ask you to understand in detail,
but regarded the capacity to predict how the world
of the first equations functions, explaining at the same time
why particles have mass.
What did Peter Higgs do?
He imagined that particles didn't actually have mass
but that in the world a sort of substratum exists,
which we call the Higgs field, to which particles without mass
stick themselves either less or more strongly
and those that stick themselves stronger, it seems they have a larger mass,
while some, like the photon, the red little brick,
don't stick at all, and appear to us as massless.
The brilliant thing about a theory like this,
isn't just that it explains a phenomenon in nature,
but that it predicts new phenomena and therefore,
getting to discover if these new predicted phenomena are true,
we can understand if the theory is real,
if nature really has chosen this mechanism to give mass,
in this case to particles.
In the case of Mr. Higgs' theory,
the interesting thing is that this substratum
to which particles stick themselves,
sometimes coagulates on itself, giving life to a new one
that we all know as the Higgs boson, but if you prefer
we could call it the blue little brick with yellow wheels this morning,
because we're amongst friends.
How does one go about looking for a new particle to see if it exists?
Well, in the case of the Higgs boson it was necessary to put into motion
the largest scientific experiment in the history of mankind.
Where I work, at CERN in Geneva,
European lab for particle physics,
there are twenty European states
plus another seventy states from around the world
that have come together to provide about 10,000 physicists and engineers,
to construct the largest, most powerful particle accelerator in the world:
LHC, the Large Hadron Collider.
What is it about?
LHC is a 27 km tunnel
dug about 100 meters underground,
inside which we take some protons -
you know, those made with the blue little bricks -
and we have them circulate on the inside,
at a speed equal to 99.99999% of the speed of light.
Think that at this speed the protons do 11,000 full laps
around the loop in a second.
Imagine the difficulty of keeping them on the path
so that they don't fall out in the curves.
And when they've achieved this speed that's so high,
we have some of them collide into some others,
so all of the energy that they've put together can free itself
to make up new particles and recreate
the universe's initial conditions, in which it is more likely
to see these new particles appear.
And what do we do to see them?
Well, at the points where the protons collide,
we've constructed gigantic detectors.
When I say gigantic -
this is Atlas, the detector that I work at -
this guy is 40 meters long and 20 meters high.
If you look at it closely, you'll see that there are some little figurines
- we aren't there usually, 100 meters underground,
but it helps give you an idea of how big this object is.
Basically this is a huge camera,
capable of taking 40 million photographs per second
of what's going on during the collisions,
and of the paths that the particles which have been produced leave.
And so my colleagues and I
- there's about 3,000 of us that work on this experiment -
we choose the best particles and photographs taken of the particles,
40 million photographs in a second, to see if there are traces
of the appearance of new particles.
And then yes!
It can happen, as was said earlier and as you've read in the newspapers,
that at a certain point in our detectors
appear some traces of an appearance of the Higgs boson
or of a blue little wagon with yellow wheels...
And yes, last 4th of July we were able to announce to the world
that this particle exists, or at least a particle
that resembles it very much and it really seems that -
a mechanism that's similar to what Mr. Higgs in 1964,
48 years ago, had invented on his chalkboard,
is what nature has chosen to give mass to particles.
Now I imagine it would be nice to tell you
that only we made this discovery,
but it's a discovery in which everyone participated because CERN,
its workers, the accelerator, and the detectors
were financed by every one of you.
Every one of you put the equivalent of about a coffee,
of the cost of a coffee a year in the last ten years,
or if you prefer, the cost of ten coffees.
And I don't know about you, but to me,
this seems like a very interesting investment
because of the return there's been.
(Applause)
But at this point I imagine
you guys sitting here are asking the same question
that Julia did in the beginning,
we've added another little brick to our pile, we've understood,
and so now what do we do?
What am I going to keep doing for work right now?
Did we solve everything? Did we learn how everything works?
I wish it was that way.
Actually there are still a lot of questions to be answered.
I will give you some examples.
For example: why is there more matter than antimatter?
Our equations tell us that for every particle
there exists a particle equal in every way except its electric charge,
like a twin in the mirror, and that when one particle
meets its antiparticle they go ... poof!
And they disappear leaving a light speck in their place,
in a process that we call annihilation.
Our equations tell us
that there's a perfect symmetry between matter and antimatter.
But if it's that way, why are we made of matter?
Because everything that we see is made of matter,
and we have to go to look for antimatter in our experiments with a little lamp.
If matter and antimatter
disappear leaving just specks of light,
why isn't the universe made of just specks of light?
We have no idea.
And why do similar particles in our equations playing the same role
have such different masses?
Why does the muon weigh 200 times more than an electron?
Why does the tau weigh 16 times more than the muon
and over 3,000 times the electron?
We have no idea.
And while we're at it, why are there three particle families when actually,
to build all that surrounds us it only takes little bricks from the first one,
the blue little bricks, the electrons and neutrons
that I showed you?
What are the other two families for?
And while we're at it, why are there three of them and not two or four or five?
We have no idea.
And where are the particles for dark matter,
those whose effects we see very clearly
when we look at the motion of the galaxies,
but which no one has ever seen traces of in our experiments?
We have no idea.
So we'll keep on asking ourselves like 4,5 year old children,
"What is all that surrounds us made of? Why is it made up this way?"
Some of us do it in front of chalkboards, like Mr. Higgs,
searching to extend our theories further,
or invent some completely new ones.
Others, like my colleagues and me,
to dig into the minuscule and deepest intimacy of nature,
with the hope of finding traces
that can confirm the goodness of our new theories
or that can give us some clues to form some alternative ones.
With this deep ambition of being able to explain
looking at the infinitely small and infinitely big
like everything functions.
Yes, because, you see, this truly is the ambition that we have,
of the history that we want to recount:
it's the history of the same bunch of particles
that I've talked to you about up to now, which about 14 billion years ago
was confined in a space not bigger than that
which is taken up by a single atom,
that of which there are three million billion billion
inside a glass of water.
Then at a certain point, for reasons again we don't understand very well,
this space began expanding,
first more quickly and then more slowly.
The Higgs field was present and gave mass to particles.
It changed the way in which the weak interaction
and the electromagnetic interaction behave.
Gravity is another one of the things we don't understand very well.
It too started behaving in a different way.
Matter annihilated itself with antimatter,
but there was a bit more, for reasons we don't grasp,
a bit of matter kept going around,
the quarks joined themselves and formed the first protons,
the electrons started to buzz around,
the first hydrogen and helium atoms were formed, in 400 million years.
The first stars started to shine, in the heart of the stars,
like in giant cosmic furnaces, the heaviest elements formed:
carbon, nitrogen, oxygen, everything that makes water
and the elements that form the life that we know on our planet.
Think that if the intensity of the weak interaction,
the one mediated by the green little bricks,
had been a bit different from what we measure,
oxygen and carbon would not have been stable in the heart of stars,
there would not have been water, there would not have been life,
and we would not be here today, to recount this history
and imagine into future.
And why is it this way?
We have no idea.
(Applause)
At the end of the 1800s, when of the particles I showed you,
the only known one was the electron, the yellow little brick,
some physicists asserted that science was finite
and that from that moment onward physics would only be occupied
by measuring in more precise ways than we already knew.
The hundred years that followed have brought numerous revolutions
in the way we see the world and have resoundingly proved them wrong,
and I can guarantee you that today
none of us would dare say something like that.
For so many things that we've discovered and we know more about,
compared to our colleagues more than a century ago,
there are so many more that we don't know about.
And if you want, awareness of this ignorance
is what pushes us to keep looking.
So it's clear that awareness of this ignorance can even give us fear,
because we're used to thinking about science as a discipline
that has answers, that we can turn to.
And instead we see it often as a discipline
that has certain answers but often has more questions than answers.
Don't believe that physicists are immune to this fear.
Albert Einstein, one of the most famous physicists of the past century, said,
"Whoever faces the mysteries of the universe
remains shocked, as if paralyzed by the immensity of what surrounds us
and of the difficulty to make sense of it."
But he also said that in the face of this shock,
the important thing is to never stop asking questions.
Like four and half year old children,
we continue to exercise our curiosity.
Thank you. (Applause)