Where are those extra dimensions in the string theory? Rob Knoops at TEDxAUBG


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)

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