Transcriber: Johannes Duschner Reviewer: Yasmina Casado González
Like a child that never stops asking why,
no matter what you answer,
so I've been driven by the question why,
all my life.
It has pushed me to dig deeper,
to go to the next level
and to the next level.
And so I've ended up
studying the smallest things we know to exist.
I invite you to join me on a journey
exploring, mining to find nature
at its smallest, most fundamental.
You will see that this smallest scale
is deeply linked with a larger scale,
the universe as a whole.
And you'll get to see that this influences
how we perceive our place in the universe.
And so we begin by taking something,
anything and cut it into smaller and smaller pieces.
Eventually you will come to a piece,
which cannot be further divided,
no matter how good the tool for cutting.
You may think that this is the atom of the elements,
but no, the atom is a composite mess;
we need to dig deeper.
But if you catch an electron,
which we know and love from electricity
swirling around the nucleus of the atom,
and you dig in the nucleus itself,
into the protons and neutrons,
to find a quark inside of them,
you will have found what we as of today
believe our fundamental building blocks of nature elementary particles;
and these are small.
They have shown no substructure
down to the size of 10 to the minus 18 meters,
that is, take a meter, cut into a billion pieces,
take one of those pieces and cut it a billion times more.
Small.
But in fact we believe that fundamental building blocks of nature
have no size at all.
If you find that hard to imagine,
don't worry, you're in good company.
That goes for many aspects of the world at its smallest scale,
where quantum physics is the name of the game.
Our human intuition has been built up
by our sensory experience in this macro world
and it simply won't do at the quantum world,
which is not to say
that we don't know what's going on there.
We can calculate and we get sensible answers.
It's just that these answers are very hard to reconcile
with how we perceive the world to work.
Let's get back to the quark in the electron.
These are matter particles
which builds all the things we see around us, ourselves included,
but they are not the full story.
In the early nineteen thirties,
a whole new component of matter was found
which in some cells behave completely opposite of ordinary matter.
Hence, it was given the name antimatter.
Don't be fooled by the name.
Antimatter is perfectly good matter.
Now, more than 80 years later,
antimatter in and of itself is old news.
We even use it actively today
within the field of medical physics for preclinical imaging
in something called PET scanners.
The P comes from Positron
which is the antimatter version of the electron.
But there is something special
and that is the relationship between matter and antimatter.
Perhaps they are the very best of friends,
perhaps they are fierce enemies;
at any rate, whenever they meet, they disappear.
They get obliterated, they annihilate
and are turned into pure energy in the form of light.
So here is where it gets interesting,
yes, downright existential.
If we go back in time to moments after the big bang,
in this early hot and dense state of the universe,
which was the infancy of our universe,
matter and antimatter existed in equal amounts.
Eventually all of that matter and all of that antimatter would meet,
but if that were the case
there would be only pure energy
left in our universe;
no matter,
nothing out of which you could build anything.
But we are here.
And we are asking ourselves this question:
"How come we are here?"
What caused this slight imbalance between matter and antimatter
to which we can thank our existence?
We don't know.
There are many things that we don't know about antimatter
and getting to know it is a challenge,
because antimatter does not linger around.
On the border between Switzerland and France
resides the world's one and only antimatter factory
at the European laboratory CERN,
that's where I work.
The people who work there
are trying to get to know antimatter better.
And as you now may appreciate
trying to understand antimatter better
is like trying to understand our place in the universe better.
We can do so,
thanks to the help of a machine called the antiproton decelerator,
whose job is to make antiprotons move slower and slower
until sluggish enough for us to capture and study.
The amounts that we get are tiny.
With a current pace
it would take us 10 times the lifetime of the universe to get one gram,
but we do get something and we are able to study it.
Currently there are five experiments connected to the antiproton decelerator;
AEgIS, ALPHA, ASACUSA, ATRAP and BASE,
all of which are trying to look at antimatter
from slightly different angles
to collectively get to know as much as possible.
I and my colleagues in the AEgIS experiment
want to see how antimatter response to gravity.
Essentially we're trying to reproduce
the famous experiment by Galileo Galilei in the 14th century
when he dropped heavy and light objects from the leaning tower of Pisa
to find that they fell with exactly the same speed.
The difference?
We want to release antihydrogen, the lightest antimatter element.
Now, antihydrogen is nowhere around,
so we have to produce it ourselves;
one of the many challenges that we are faced with.
But let us focus on the basic idea, the basic question
Imagine that you held an apple made of antimatter in your hand,
an anti-apple,
and you let it drop.
How would it fall?
Just like an apple made of ordinary matter would
or would it fall slightly slower,
perhaps much faster,
or —and this is the real oddball here—
would it fall upwards.
It's not expected that it falls upwards,
but no one really knows
because no one has performed the experiment.
So let us entertain the idea for a while
that antimatter behave so unexpectedly as to fall upwards.
We believe
that there are no large structures
made of antimatter out there in the universe
and I'll explain why.
For this you need to recall that whenever matter antimatter meet
they get turned into pure light.
So if there were a region of antimatter out there,
it would have to border to a region of matter,
after all we are made of matter,
and from this horizon light would stream.
So we look up into the night sky,
we peer deep into the universe and we see no such light.
But if antimatter falls upwards
when released here on Earth,
it means that matter and antimatter gravitationally repel each other
which means that the regions wouldn't meet
and there would be no such light for us to see,
in which case for all that we know
there could be an anti-world somewhere out there.
Now let us for a moment go back to quantum physics.
When you dig to find nature at its most fundamental,
you will eventually, inevitably encounter symmetries.
Symmetries are deeply woven into particle physics;
indeed it's the heart of the theory.
Symmetries decide what may or may not happen
and which forces are at play.
With a symmetry we mean
that something look the same before and after a change,
that it is invariant to the transformation
like a uniform ball.
If you twist it around it looks the same
no matter what, it is symmetric.
Likewise, if we performed a physics experiment here today,
we would get the same result
as if we would have performed that experiment tomorrow
on the other side of the globe,
which means that the physics involved
has to be invariant symmetric
with respect to changes in time and position.
We expect nature in its simplest and most fundamental form to be symmetric
and it is for the most part.
So we expect nature to be symmetric
in her gravitational treatment of matter and antimatter;
that they fall in the same way.
So it is not at all expected that antimatter falls upwards,
but it is not impossible either.
Albeit not plausible, it is theoretically viable.
We simply don't know,
before we go out and have a look for ourselves.
And we have been surprised before.
I can tell you that when the cosmic, microwave background radiation
was discovered initially,
pigeons were blamed for obstructing the measurements
by littering on the experimenters antenna.
Or I could tell you that when the muon particle was discovered,
surprised and perhaps likely dismayed theoretical particle physicist
blurted out: "Who ordered that?"
Oh, yes, nature certainly has the capacity to surprise us,
even shock us as it did
when we first have a look at a particular symmetry
called "charge parity".
Charge parity flips the electrical charge
and all of the spatial coordinates.
Left becomes right,
forward becomes backwards,
up becomes down.
And now you will get to know
what the real difference between matter and antimatter is.
It's the flip of the electrical charge.
Whereas an electron has negative electrical charge,
the positron has positive electrical charge.
So charge parity transforms a matter world
into an antimatter mirror world.
And we expected the rules for these constellations to be the same;
that the situation was symmetric.
So when it was found utterly unexpected
that nature violates charge parity,
physicists felt like
the ground had been removed from underneath their feet.
That charge parities violated means
that the processes involving matter and antimatter
move at slightly different speeds,
which could be the explanation for why matter won over antimatter
in the early universe.
But in our standard model of particle physics,
the processes that violate charge parity are simply not strong enough
to explain the apparent asymmetry between matter and antimatter,
which we observe in our universe today.
So we have to look further.
So we know now that antimatter behaves unexpectedly.
The question is how much and in which ways
and that's what we're trying to find out.
We will soon learn more about antimatter from the ongoing experiments.
We are even upgrading.
Soon a new machine called ELENA will go online
improving upon the job that the antiproton decelerator does.
It will provide more antimatter for us to study.
Most likely, we will find
that matter and antimatter fall in exactly the same way,
in which case, we'll have to look further
for solving the mystery of the missing antimatter.
Why there is something instead of nothing.
We know
that there are several missing pieces to our unterstanding of nature
and we are continuously searching,
probing with a range of multi various experiments
to get to know the universe and our place in it better.
Ultimately, that's what we humans do.
We search for understanding,
we seek to learn, we explore.
It's a fundamental part of our humanity.
So I would like to end on a personal note with an encouragement to you.
Nurture your curiosity.
I believe it's the best thing we can do for the world.
Being open and skeptical
will bring you the humbling experience of getting surprised
and having to revise your view upon the world.
I'm rather sure that when you look at me,
the first thing that meets the eye is not a scientist,
but that's just the thing.
We're all scientists at heart,
no matter what we dress like or it look like, who we are.
And we were all active scientists at one point in our life,
exploring, performing experiments to get to know our surroundings better
when we were kids.
So find back to your inner child,
never stop asking questions,
cultivate your curiosity.
You never know
when you might stumble upon something unexpected.
(Applause)