Translator: kitty bian Reviewer: Xinyi He
Around the clock the sky is raining silver and gold
and all kinds of other elements
carbon, copper, hydrogen, oxygen, etc.
Luckily we don't get soaked with these rain particles
because we have a protective umbrella that we call atmosphere.
These particles travel near the speed of light
toward us from all directions constantly
Then, once in a very long, long while,
one of the fastest bits of matter hits the top of the atmosphere.
We call these very rare particles ultra high energy cosmic rays.
Let's start with the lowest energy cosmic rays.
The lowest energy cosmic rays are thrown at us by the Sun
in a stream of charged particles known as the solar wind.
Some of us have actually seen these particles
and we call them the Northern Light.
The rate at which these particles arrive
to the top of the atmosphere falls
very very rapidly with increasing energy.
This makes sense because what it says
is that the faster you wanna accelerate
these particles, the harder it is.
And therefore, they are more and more rare to reach us.
So for example, these lowest energy particles
hit every square meter of the atmosphere
10,000 of them every second
we know even higher energy particles
for example we know of sources of high energy
cosmic rays in our own galaxy, the Milky Way
for example this is how rapidly
this rate falls.
If you look at a particle with
a thousand times higher energy
the rate of arrival at the atmosphere is
a billion times lower
a billion with a bs in bernie
This means that that same square meter of
atmosphere, instead of being heated by
10,000 particles per second,
now at the center she's heated by
10 particles every hour.
So that's how steep this is.
And this is...I stopped at the center intentionally
because this is the energy range we have mastered
for example here we know how to
produce irons.
Here you have a very young and handsome
despite the short hair,
playing with his vibes source of negative ions
We also know how to accelerate sub-atomic particles.
This is a ? posing for a photo
next to the Tevatron
this circular particle accelerator
accelerated protons and antiprotons
along this 4-mile-long ring
at the energy of 1 trillion electron volts
which means that these protons were
travelling along the 4-mile-ring at
a speed of 99.99995% of
the speed of light.
This was the highest energy particle accelerator
until the large Hadron Collider was built
near Geneva, Illinois.
Near Geneva Switzerland.
In this machine, this machine is
17 miles long, is the largest single machine
in the world, the most powerful accelerator.
Here, portons go through this 17-mile run at
7 trillion electron volts, or
99.999999% of the speed of light.
So many nines, which means that
in one second, these protons go around
the 17 miles more that 10 thousand times.
Ok? This is the most impressive machine
most complex experimental facility that
we can build.
And particles of the same energy
bombard thisconstantly
so there are sources out there
that can accelerate these particles
to this energy, and for my pretty graph
you can already tell that there are sources
that can go to even higher energies.
In fact, some cosmic rays
there are sources of cosmic rays that can
accelerate these cosmic rays to a power
that we cannot even explain yet.
Some of the sources may lie in other
galaxies, where some very exotic objects live,
like supermassive blackholes, which may be
the drivers of this acceleration mechanism.
We have actually detected cosmic rays
with energies 100 millions times higher
that what we can do on earth with
the most powerful machine.
This energy is so huge, this acceleration
so big that these particles are extremely rare
So the rate of arrival of these particle
to the top of the atmosphere is
one per square kilometer every century.
That is very rare.
So we want to detect these particle
the direct observation of cosmic rays
can only happen on top of our
protective umbrella, so on top
of the atmosphere, and these high energy
cosmic rays are so rare that it's impossible
to leave the detector in the space
big enough to capture significant number of
these cosmic rays.
So we have to do it on the ground.
And for that we put
detectors on the ground and we
use the fact that when these cosmic rays
hit the top of the atmosphere,
the collisions with air molecules create
a large cascade of secondary particles.
These extensive showers have billions of
secondary particles that fall
and reach to the ground, covering
a huge area of many square miles.
So we put detectorsand we cover a
large area on the ground.
This is a particle detector.
I know it looks a lot like a water tank,
but it's actually a big water tank, because
12 tons of ultra pure water and
instruments that can detect the
secondary particles when they reach the ground
at that point. So we deploit 1600 of these
detectors in western Argentina,
and each detector is one mile apart in a
triangular grid covering a total area
of 3000 square kilometers
This is 10 times the size of Paris
This is the size of the whole state of
Rhode Island.
So just to give you and idea I will compare
these two huge areas we cover with detectors
with the two largest cities in the world
This is New York metro area
Her you have Manhattan,
Manhattan is only like 60 square kilometers
This is Tokyo, so if you recognize
the Yamanote line, it's this one right here
And for the local people in the audience,
we have put detectors from Lewis Town to
Huntingdon, Tyrone, Philisburg, Lock Haven
There is one detector every single mile
covering that whole area.
This is in the provice of Mendoza in Argentina
This is the provice where all the good
? come from. And I know what you are thinking
there's no correlation between that and
being located there.
This is the footprint, this is actual data
from publicly available from the
observatory. This is the footprint
of one sub-atomic particle,
say a proton for example,
that hit the top of the atmosphere
with ultra high energy.
It collided within the atmosphere and
it created these extensive secondary particles
that spread and left signals on the ground
on each one of these detectors covering
the whole area of more that
20 square miles.
One single proton hitting the top of the atmosphere
And I know what you are thinking
right now at this point,
is that this is cool, I don't know
about sexy, but this is cool, and
but why is this important?
What are you hoping to learn from this?
And more importantly, why should
you be intersted in the study
of cosmic rays?
These are all excellent questions, and
they are all related.
Cosmic rays are messengers from space.
They are real samples of the
star stuff that have travelled millions
of years before reaching us.
We use cosmic rays to infer
useful properties about our galaxy
such as its composition,
its basic structure. In fact,
cosmic rays are one of the very few handles
we have in which we can sample real matter
from protons all the way to the
heaviest elements, coming from
beyond our solar system.
By identifying these diverse nuclei,
we are hoping to unravel the mechanism
that can actually produce those nuclei.
We want to know how they are produced,
we want to know how these nuclei can
reach near the speed of light,
we want to know what these
nuclear collisions that occur in super ?
Just to think about this.
The iron in your blood came from
a supernova billions of years ago
in our own solar neighborhood.
Cosmic rays also opened the world of
sub-atomic particles.
We discover the positron,
the first particle of anti-matter,
the positron was discovered in the
cosmic rays. We learn that
when energy is converted into mass,
it shows up as matter and anti matter
in equal parts.
This is just a cartoon of a shower from
a cosmic ray. These are actual tracks from
my electrons and anti-electrons,
aka a positrons.
Before we learned how to build our own
particle accelerators, this natural radiation
was the only way of studying the
sub-atomic world.
And again this is pretty cool, but
you could still say
'you haven't touch my reality.'
And I'll give you one example,
that 'P' in PET scan stands for positron.
Not only we discover anti matter,
we learn how to use it.
We learned that when anti-matter
meets with matter, they annihilate,
and they emit energy.
So a PET scan is a nuclear medicine imaging
that by detecting these energy can show
the structure and function of
organs and tissues.
So this is what we do.
Fundamental research is what drives our reality.
So we helped unravel new laws of physics,
we helped to discover new particles,
and ou can always say
so ok, how about my reality
and, you know,
Can you harness this sort of high energy.
That's a typical question.
Can you get all this ultra high energy.
How can you improve my quality of life
with this cosmic rays
？I don't know.
I guess I'm like a character in
Winnie the Pooh, I'm not smart enough.
In my defense, though,
when Anderson discovered positrons,
he was not thinking about PET scans.
When Faraday discovered electromagnetic induction
he was not thinking about
generating electricity.
When Einstein figured out General Relativity
he was certainly not thinking about the
GPS in your smart phones.
They are all doing fundamental research.
They were all trying to figure out
how the universe works.
So my fundamental question is
how do these cosmic rays reach these
ultra high energies.
We will discover new laws of physics,
we will find super heavy particles that
we cannot possibly recreate on earth.
I don't know.
But what I do know is that this
acceleration mechanism is truly impressive.
If we want to build a machine to
accelerate protons to ultra high energies
this ring, instead of 17 miles,
there are clear conference on the rings
for ultra high energy protons would be
comparable to the orbit of Mars.
So that's something not even
Hollywood can make.
So that's why for the past twenty years
my reality has been driven by the hunt
of the fastest particle in the universe.
Thank you.
(Applause)