Exploring the Forces of Nature
Having a “Blast” doing Physics!
Manuel Calderón de la Barca Sanchez
UC Davis
Let me tell you…
• a little about me.
• why did I choose to study Physics?
• what is this “blast” I’m talking
about?
• How do Science and Physics help
us learn about our world?
My early education
• Born in Mexico, in Mexico City.
• Goal in middle school: Wanted to
work with computers.
– Liked programming (and video games!).
• High school:
– Physics: help us understand our universe
– Questions:
• Why is there night and day?
• What are we made of? How do we know?
• How does the sun shine? Will it ever stop
shining?
– Math: a way to check if our answers to these
questions are correct.
• Geometry: How do we know Earth is round
without leaving Earth? How big is it?
A place for everything: College
• College: Majored in Engineering
Physics
– Computing, Electronics, Math, and
Physics.
• Learned many wonderful things
– Same behavior:
•
•
•
•
Apples falling from a tree
Planets around the sun.
Galaxies and the universe.
Gravity!
More questions to be asked…
• Learned there are many
more questions!
– I wanted to keep doing Physics!
• Just one example:
• What are we really made of?
• Is matter continuous or
lumpy?
• Can we divide any chunk of
matter infinitely many times?
• Where next? Graduate
school.
What’s the matter?
• Nuclear and Particle Physics:
– Study the blocks we need to build all of the
things we see.
• Take a piece of coal, and cut it…
• keep cutting, and cutting and
cutting…
– When does it stop being coal?
• Molecules: Smallest unit of a substance that
retains its chemical and physical properties.
– Does it burn? Does it react with oth
• Current knowledge: molecules a group of
atoms, held together by electrical forces.
– There are millions of molecules!
• Water, lactose, carbon dioxide, wood, cotton,
rubber, proteins, …
– However, these are made of only 100 distinct
units: atoms.
The Elements
Can the atomic elements be cut?
• Yes! This was done in the 1900s and
1910s.
• There are 3 particles that make up ALL the
elements
– Proton, Neutron and electron.
An atom
• A Picture:
– nucleus with most of the
mass in the center
electron
• How do we know? Ask
me why later!
– electrons around it
neutron
• Note: scale is totally
wrong!
– Ask me why later!
• Can we cut a nucleus?
– Yes, eventually you get
only protons and neutrons.
– Where do the names come
from?
• Can we cut a proton or
a neutron?
proton
Cutting protons and neutrons
• Yes, we can cut
protons and neutrons!
• We find
quark
neutron
– Quarks: “three quarks for
muster Mark”
– Gluons: “the strongest
glue”
proton
How do “Quarks” make proton and
neutrons?
• Proton: electric charge +1.
• Neutron: electric charge 0.
• Puzzled a lot of people…
– Needed objects with fractional
charges!
up:
+2/3
up:
+2/3
• Can be done with two quarks:
– up : electric charge +2/3
– down : electric charge -1/3
down:
-1/3
Quarks and gluons in a proton
Radius of a baseball:
5 cm = 5 x 10-2 m.
Radius of a proton:
~1 fm = 1 x 10-15 m.
A proton is:
10,000,000,000,000
smaller than a
baseball
•
Center for Subatomic Structure. Physics Dept. U. of Adelaide, Australia. 2003.
Quarks and gluons are interesting!
– They make up protons and
neutrons.
– But we never see a single
quark, or a single gluon.
• We can melt the atom:
– “free” the electrons and protons
in an atom
– electric “plasma”: The sun
• Can we free the quarks?
– It needs to get hotter than the
sun!
Melting the proton
Quarks are quirky:
We never see quarks and gluons
by themselves.
To free them, we need to melt the
proton.
• heating
• compression
 quark-gluon plasma !
Hadronic
Nuclear
Matter
Quark
GluonMatter
Plasma:
(confined)
Freed
the quarks!
Imagine…
You live in world so cold there is only ice…
Your theorist buddies compute that heating
ice produces something new: call it water…
You don’t have a way to heat ice…
So you put millions of ice cubes in an iceaccelerator
Send them at 99.995% of the speed of light
to collide
Generating thousands of ice-cube+ice-cube
collisions per second…
And you watch it all from the vicinity of Mars!
Collisions at the highest velocities!
• Fast:
– 99.995% of the
speed of light
• Massive
nuclei:
– About 200
nucleons smash
against 200
nucleons
• Many Quarks!
• Collisions:
– kinetic energy
into heat
Producing a mini-bang in the Lab
Collisions in the Laboratory
• What do I work on:
•Collider experiments.
• We smash particles
together!
• Use a large collider.
• See what comes out of this
blast.
New York City
Relativistic Heavy Ion Collider (RHIC)
PHOBOS
PHENIX
2 km
RHIC
BRAHMS
STAR
v = 0.99995c = 186,000 miles/sec
AGS
TANDEMS
Having a Blast in my experiment!
PHOBOS
PHENIX
RHIC
BRAHMS
STAR
AGS
TANDEMS
STAR: One experiment, ~500 Scientists!
• How do
• teach us about our world?
– Example: the discovery of atmospheric pressure.
What did we know about air?
– Explanation in 1600s: The vacuum created in the
straw pulls on the water. “Nature abhors a vacuum.”
– Observation: water can only be raised in a tube up to
10.28 meters.
– Making a stronger pump to improve the vacuum
made no difference.
• Evangelista Torricelli: “Aristotle’s
explanation is wrong. Air has weight.”
vacuum
• Aristotle thought air had no mass, no
weight.
• Up to the 1600s this was accepted.
• Why does water go up when we suck on a
straw?
Torricelli’s Idea: Scientific reasoning
• If air has weight, it is not unlike water, only
“lighter” (less dense).
• What happens when we dive in a pool as we
go deeper and deeper?
– What do your ears feel?
– Weight of water exerts pressure on us!!!
• We are in a “pool” of air!
• What happens if we create a vacuum above?
– We remove air pushing on us.
– Imbalance! Air outside pushes,
• What does this mean for the column of water?
– Weight of the column of water must balance
• What if we use a “heavier” (denser) fluid in
the tube?
vacuum
– Air is pushing on us! “Air pressure”
• Density: how much mass is
in a given volume.
– Density of Mercury: 13.53 g/cm3.
– Density of Water: 1 g/cm3.
• If water reaches 10.28 m in
the tube, how high will
mercury reach?
vacuum
Using a very dense fluid: Mercury.
Calculation: the power of Math!
Weight air = Weight water
Weight air = Weight mercury
But air is the same in both cases!
Weight air = Weight water
• Weight = density x volume
• Vol: area of cylinder x h
• But area of cylinder is the same in both cases!
Water density x area of cylinder x water height =
Mercury density x area of cylinder x mercury height
• Shorthand: Algebra!!
– Dw x A x hw = Dm x A x hm
– hm = hw x (Dw/Dm) = (10.28 m) x (1/13.53) = 0.76 m
vacuum
vacuum
•
•
•
•
How science works
• Sometimes accepted wisdom does not match what
we see.
• A new idea is needed.
• Idea must be tested.
• Calculate expected behavior: Use MATH!
– Predict the result of an experiment before you carry it out!
• Perform experiment: Check what Nature
says!
– Nature is always right.
• If it works every time we try it, we trust the
idea more and more.
– Idea must work everywhere, not just in your lab: in another
place, in another country, maybe in another planet…
• We can use the new knowledge to our advantage:
– Example: mercury barometer: measure changes in atmospheric
pressure.
Pressure demonstration:
• Creating a vacuum
in a sphere:
– Very little pressure
inside
– Atmospheric
pressure outside
• Air molecules
outside win!
• They push
spheres together:
– Force can be very
large!
Pressure on Magdeburg Hemispheres
• Atoms banging on walls: pressure
– 1 atm = 10.28 m of water = 760 mm Hg
• Equivalent way to use pressure:
mass/area
– 1028 cm (1 g/cm3) = 1028 g/cm2 =14.7 lb/in2
• How much mass can they support if we
create a pressure difference p of 400
mm of Hg?
– Assume effective area A is (p (5 cm)2)
– So (p x A) gives the total mass that the spheres
can support due to pressure difference:
approximately
– (1.028 kg/cm2) x (400/760) x (p (5 cm)2)
– mass = 42 kg
Science and Physics as a Career
• Why I like it:
– I get to explore how the universe works.
– I work with people from all over the world.
– What we find applies to everything!
• In our lab, halfway around the world, on the moon, in
another galaxy…
• Why is it beneficial:
– Improve our understanding.
• One scientist can help clear up thousands of years of
misconceptions. Examples:
• Matter is made of tiny particles (not continuous).
• Even air is made up of particles, it has weight and
exerts pressure.
– Cool applications!
• Our knowledge of matter and the forces improve our
health, our life.
• Maybe you can help produce the next
breakthrough!
– Medicine: e.g. cure of diseases.
– Technology: tackle global warming.
Additional Material
Cathode Rays: e-. discovery
• 1897:
Joseph John “J. J.” Thompson
– Studied “rays” present when applying High Voltage between two electrodes
in a vacuum tube, and established their nature.
• First experiment: Rays bent in Magnetic field.
• 2nd Experiment: Rays bent in Electric field (Shown below)
• 3rd Experiment: Measure mass/charge. Found it to be 103 times
smaller than mass/charge for H+ ion.
• Conclusion: Cathode rays are made of particles (“corpuscules”).
1906 Nobel Prize
Thompson’s Plum Pudding Model.
• Atoms: Two components with opposite
charge.
• Thompson’s model: electrons free to
move in a region of positive charge.
–
–
–
–
–
Electrons are negatively charged
Blob is positively charged
Total charge of atom is zero.
Pros: Explains why atoms are stable.
Cons: Can’t explain light emitted from atoms is
only of certain colors, not of ALL colors.
Rutherford:
Collisions between particles – metal foil
• Shoot alpha particles at a thin gold foil
• Expected results:
– Small deflection angle
• alpha particle is dense
• + charge is spread out
– all particles deflected the same way
• + charge fills space uniformly
Rutherford’s Lab
(Done by H. Geiger and E.
Marsden
was an undergrad!
Marsden)
• Most alpha particles passed through foil
– No deflection!
• Rutherford said “What about large
deflection angles?”
• Large deflections observed!
– Some even reversed direction!
Rutherford Model: Like a “solar
system”
• Massive, + charged nucleus
– Located at the center.
– Hydrogen: mp/me = 1836
• Light, - charged electrons
– Located orbiting far away from
nucleus.
• Most of the atom is empty
space.
• Size of hydrogen: ~10-11 m
• Size of nucleus: ~10-15 m
The standard model.
• 6 types of
quarks:
“flavors”.