Transcript How to measure things you can’t see?

How to measure things you can’t see
Particle physics
Dr. Julie Roche
I will tell you:
-What I study (really small particles you can’t see with your eyes)
-And How I study it (by throwing things at them)
But I would like to start by playing a little game with you:
Take a piece of paper and draw a physicist.
Who’s the physicist?
3: both of them
are physicists
1
Albert Einstein
Physics Nobel Price
2
Marie Curie
Physics Nobel Price
Chemistry Nobel Price
Who’s the physicist?
3: both of them
are physicists
1
J. Webster
Professor of English
Ohio U
2
J. Matthews
Professor or Physics
MIT
Who’s the physicist?
3: both of them
are physicists
1
G. Mavimbela
PhD student in Physics
Ohio U
2
A nice girl in front
of a computer
Who’s the physicist?
2
1
2
3: both of them
are physicists
To finish our little game:
Look back at the physicist you have drawn.
Most people will draw an old white man (à la Albert Einstein).
But in reality, physicists come in all genders and all races.
They also come from all social background:
do you know graduate school in Physics is very often FREE?
You can become a Physicist if you want to.
What I really want you to tell you today is:
You don’t have to choose to become a scientist today but
-Act now to keep your career options open (and easy).
Take all the math and science class you can.
Get involved in science fairs and other extra-curricular science activities.
-Nurture your own goals and talents.
Read, watch and listen about science, visit web sites, museums, etc…
Talk about your future with your parents, teachers, friends.
How to measure things you can’t see
Particle physics
Dr. Julie Roche
I will tell you:
-What I study (really small particles you can’t see with your eyes)
-And How I study it (by throwing things at them)
What is the world made of?
We believe the world is made of 12
fundamental particles.
Fundamental means that these
particles are not made of
anything smaller.
What holds the world together?
By observing the simplest objects
the fundamental particles form,
we can learn about the four most
fundamental forces of our
universe.
The trouble is that we can’t see
with our eyes these simplest
objects because they are so
small.
BY THE WAY,
HOW DO WE SEE ?
To see, we detect with our eyes the information of
the bounced-around light.
Light is actually a wave of energy.
Light carries information about the physical
world because it interacts with what it hits.
Other animals, like dolphins and bats, emit and
detect sound waves. In fact, any kind of reflected
wave can be used to get information about the
surroundings
Pretend that you are unlucky enough to fall
into a cave without a flashlight.
However, you are lucky enough to have a
bucket of glow-in-the-dark basketballs.
Suddenly, you hear a snuffling sound.
WHAT’S THAT ????
Basket balls:
It’s a big thing…
Tennis balls:
No much better
Marble balls:
It’s a bear: RUN!!!
The morals of the preceding story are:
•
Don't throw things at hungry bears
• To gather the most information about an object, use a probe
that matches the object you want to study.
The tool I use to measure the proton is the
Thomas Jefferson National Accelerator Facility
BY THE WAY,
HOW DO WE SEE ?
Just as light carries information about the physical
world because it interacts with what it hits,
electrons scattering of small target particles
reveal the shape and size of these objects.
Here are a two examples with light.
Use scattering to guess the shape of an object
The pink lines represent rays of light. The light bounces off
an object that is underneath the cloud.
What is the shape of the object under the cloud?
1. Square
2. Circle
3. Triangle
Use scattering to guess the shape of an object
The pink lines represent rays of light. The light bounces off
an object that is underneath the cloud.
What is the shape of the object under the cloud?
1. Square
2. Circle
3. Triangle
Change the energy of the probe to guess the
shape of an object
BY THE WAY,
HOW DO WE SEE ?
To see, we detect with our eyes the information of
the bounced-around light.
Just as light carries information about the physical
world because it interacts with what it hits,
electrons scattering of small target particles
reveal the shape and size of these objects.