Translator: Maria K. Reviewer: Queenie Lee
What is the smallest thing you can imagine?
A peanut, an atom, this logo?
(Laughter)
From the chair you are sitting on to the walls, or even my hands.
What are they made of?
Of course, in our chemistry classes,
they taught us, yet, this is made of atoms and molecules.
But these, in turn, they're even made of even smaller particles
that we call protons and neutrons, and there's electrons going around them.
But, we physicists, we're smarter than chemists,
and I don't think there're chemists in the room; I can say this.
And we can look even deeper into this matter.
And we see that even a proton isn't the smallest.
A proton consists of even smaller particles called quarks.
And at CERN,
these are actually the questions we want to answer.
We want to answer three questions:
Where do we come from?
What are we made of?
Where are we going?
And there's actually a fourth question -
that's: What are we having for dinner tonight?
(Laughter)
But there are basically two ways of answering these questions.
There's a first way, that's by using logic and thinking about it,
and it's called theoretical physics.
And that's me; I am a theoretical physicist.
And another way is to make your hands dirty and to do experiments.
And somewhere along the line, the theory and the experiment should agree.
Now, how does one exactly do an experiment?
How does one try to figure out what's inside an atom?
How does one figure out what's inside a proton?
There's not a single microscope strong enough to look that deep.
Well, the way we do this is we take two protons
and we smash them together as hard as we can.
Then, from all the pieces that come out, we try to figure out what happens.
Now, while doing this, there's something really interesting, what happens,
and that is that some of the pieces that come out of this collision
were not even in there in the first place.
So by hitting protons together very, very, very fast
you can actually create new matter.
And one of the things that we might hope to do
is that some of the particles that get created in these collisions,
that's something that we don't know yet what it is,
that we maybe have found, like, a new building block of nature.
Now, how is this done in practice at CERN?
We have this huge tunnel called the Large Hadron Collider,
and we use this to give an incredible speed to protons before they are collided.
And to give you an idea how fast these protons go in this tunnel,
at top speeds, they would go around the Earth
about seven and a half times per second.
That's huge.
But anyway,
(Laughter)
I'm a theoretical physicist,
so this is for engineers and experimentalists to worry about.
I'm here to talk about theoretical stuff.
So what we get to do
is we get to think about what we don't understand yet.
And
one of the things that we don't understand
is, for example, when the astronomers,
when they take their telescope and they look into the sky,
and they see that the star is moving away from us,
they take their telescope, they look into another direction,
and this star is moving away from us as well.
And suddenly they noticed that all the stars in the universe
are moving away,
so the universe seems to be expanding.
But this is okay,
I mean, somewhere in the past, there was a big bang,
and the universe started to expand.
But then they looked closer, and they noticed something strange.
The universe seemed to be expanding at an accelerating rate.
That means that the stars are moving faster and faster and faster away from us.
Now why is this strange?
You would expect that since the universe, the galaxies, our solar system,
it's all made of matter.
So something like gravity would be able to pull it back together.
But actually, the opposite thing is happening.
There's something pulling the universe apart.
And we don't really understand how this works,
so what we then do in physics is we give a fancy name to it.
And we call this thing pulling it apart, we called "dark energy."
And there's one way that we don't know how to describe it very well,
but we can put a number to this, like, "Do you know how strong this is?"
And this number, we call the cosmological constant.
Why am I saying this?
I will need it later.
So remember "cosmological constant."
Now, one really strange thing about gravity
is that we don't really know how it works.
And this might sound strange to you, because, of course, some long time ago,
Newton, he found out, oh, the apple falls down a tree.
Or we understand by the laws of general relativity of Einstein
how the Earth goes around the Sun.
But if you were to zoom in, in gravity, you look at it very closely,
then we don't really know how it works.
Yeah, you might have noticed,
I'm the guy that's going to talk about nerdy all the time.
Let me compare this to light, for example.
If you zoom in on light waves,
then you see, like, very little particles called photons.
And the exact same thing,
we don't know how to describe it for gravity.
That's an open question; we don't know.
Well, actually, there are a lot of ideas.
Because I mean, if we don't know,
someone has an idea, another person has an idea.
And there's only one idea I would like to talk about today.
And it's called string theory.
Of course, at some point along the way, this is still an idea
until somewhere in the future we might find an experiment that says,
okay, this is the right way or you guys are completely crazy,
that something else is the truth.
So string theory says that if you would zoom in, in matter,
and you look very, very, very closely
that you would see that matter consists of little vibrating strings.
And like all the notes on a guitar, you can play different notes of music,
the different notes on these strings
would correspond to all the different particles we can see in the universe.
So the basic building blocks of nature would be these little strings.
But then, something strange happens.
When this theory has to be consistent,
at least, for mathematicians - and mathematicians are very smart -
if they tell you something is true, it's true.
And they tell us that this theory only makes sense
if the universe is made of ten dimensions.
Now, what is a dimension?
Well, I have an "x" dimension, a "y" dimension, and a "z" dimension.
And that's three.
And we physicists, we like to call time a dimension as well.
So, let's say we have four dimensions that we can see in this room,
which means that if string theory were to be true
and the universe is ten-dimensional,
where are those six extra dimensions?
Well, we think that the solution is that they are rolled up,
and they're so small that we cannot see them.
Now, let me explain this a bit better.
Imagine I were a little ant, and I went to walk around on this bottle.
I can walk around clockwise or counterclockwise.
And at some point, I will end up at the same point again.
This is one of the rolled-up dimensions.
Well, in the other direction, imagine this bottle being much longer,
this ant can keep walking for a much longer time.
Now, the idea is that the extra dimensions, they are rolled-up,
and they're so small that we cannot see them,
not even with the best experiment that we have.
Not even the LHC has been able to notice that the extra dimensions are there.
Actually, they have been looking for extra dimensions at the LHC,
but I think that chances are quite small that they will find them.
But don't tell this to my employer.
(Laughter)
So we have these extra dimensions that are rolled up.
And that gives room for us theorists to think:
How are they rolled up?
I mean, of course, for example, I want to roll up two dimensions.
And I can make a bowling ball.
I can walk in this direction, this direction,
and I will end up at the same spot again.
So it's okay; two dimensions are rolled up.
But then, I can also make a doughnut.
It's something completely different.
But it's also two dimensions rolled up.
Or I can think of even something more complicated, a pretzel, for example.
And mathematicians, they come up with even more complex stuff,
like they call Calabi–Yau manifolds, but let's not go in that direction.
And then you can even just think about how complex,
how many possibilities there are
if you want to roll up the six extra dimensions.
And some very smart people have put a number to this.
And it seems that there's more possibilities
to roll up these six extra dimensions than there are particles in the universe.
So we have huge ideas
that we can choose from,
like how can they look like.
And then the interesting thing
is that for every different configuration of these extra dimensions,
the laws of physics and the four dimensions that we know
change.
So, somehow, our goal is,
if you want to make sense of string theory,
to find configurations of these extra dimensions,
so that the laws of nature that come out of string theory
correspond to the laws of nature that we can find here, in this room.
And what I've been doing in the last months
is exactly this cosmological constant.
I've been trying to find some configurations,
which reproduce the cosmological constant,
like we think it is,
like the experimentalists tell us it is.
To give you a heads-up, I haven't found it yet.
(Laughter)
But some day maybe.
But
have you noticed anything?
I started talking about the smallest of the smallest.
I was interested in what is the universe made of,
what are the basic building blocks of the universe,
and I ended up talking about something as big as the universe itself.
So, somewhere,
the smallest of the smallest and the biggest of the biggest
seem to be related.
If we want to understand these basic building blocks of nature,
we have to understand the universe as a whole, or vice versa.
If we want to understand the universe as a whole,
we'd better try to understand
what the basic building blocks of nature are.
Let me compare this to something that happened in the past.
People have been wondering how the Sun gets its energy
for ages before we found out.
It was only until we managed to understand nuclear interactions
that we managed to understand how to apply these nuclear reactions
like the smallest nuclear interactions
between something as small as an atom and something as big as a Sun,
how we found out how this works.
So maybe someday, we can look even deeper in matter
to find out about something even bigger than the Sun,
about something as big as the universe itself.
Thank you.
(Applause)