Mysteries Needing Explanation
1) Where does structure come from?
2) Why is the overall distribution of matter so
uniform?
3) Why is the density of the universe so close
to the critical density?
An early episode of rapid inflation can
“solve” these “problems” in the standard
picture!
Inflation can
make all the
structure by
stretching tiny
quantum ripples
to enormous size
These ripples in
density then
become the
seeds for all
structures
How can microwave temperature be nearly identical on
opposite sides of the sky?
Regions now on opposite side of the sky were close
together before inflation pushed them far apart
Inflation of
universe flattens
overall
geometry like
the inflation of a
balloon, causing
overall density
of matter plus
energy to be
very close to
critical density
The major problem with INFLATION is it is non-decideable.
It cannot be disproved!!!
It is also pretty arbitrary and has no real physical reason to
exist.
And what causes the rapid expansion?
What is everything in the universe made of?
What are the fundamental particles?
bricks
sand
concrete
silicates
atoms
protons, neutrons, and
electrons
?
Physicists have discovered that protons and neutrons are
composed of even smaller particles called Quarks.
As far as we know, quarks are like points in geometry. They're
not made up of anything else.
After extensively testing this theory, scientists now suspect
that quarks and leptons like the electron are fundamental
(cannot be subdivided).
The Modern Atom
Electron (size < 10-18 m)
e
Quark (size < 10-18 m)
Proton (size < 10-15 m)
Electrons are in constant
motion around the
nucleus, protons and
neutrons jiggle within the
nucleus, and quarks jiggle
within the protons and
neutrons.
u
u d
e
d
d
u
Nucleus (size ~ 10-14 m)
Atom (size < 10-10 m)
d
u d
u u
d
This picture is distorted. If we drew the atom to scale and made protons and
neutrons a centimeter in diameter, then the electrons and quarks would be less
than the diameter of a hair and the entire atom's diameter would be greater than
the length of thirty football fields! 99.999999999999% of an atom's volume is just
empty space!
An atom is tiny, but the nucleus is ten
thousand times smaller than the atom
and the quarks and electrons are at
least ten thousand times smaller than
that. We don't know exactly how small
quarks and electrons are; they are
definitely smaller than 10-18 meters,
and they might literally be points, but
we do not know.
We have now discovered about two hundred particles (most of which
aren't fundamental). To keep track of all of these particles, they are
named with letters from the Greek and Roman alphabets.
Of course, the names of particles are but a small part of any physical
theory. You should not be discouraged if you have trouble
remembering them. Take heart: even the great Nobel Prize winner
Enrico Fermi once said to his student (future Nobel winner) Leon
Lederman,
"Young man, if I could remember the names of these particles, I would
have been a botanist!"
Particle
Composition
Theorized
Discovered
Comments
Electron e− elementary (lepton)
G. Johnstone Stoney (1874)
J. J. Thomson (1897)
Minimum unit of
electrical charge, for
which Stoney
suggested the name
in 1891.[10]
alpha (α)
comp (atomic nucleus)
never
Ernest Rutherford (1899) Proven by Rutherford
and Thomas Royds in
1907 to be helium
nuclei.
Photon γ
elementary (quantum)
Max Planck (1900)
Einstein (1905) or Rutherford (1899) as γ rays
Necessary to solve
the problem of black
body radiation in
thermodynamics.
Proton p
composite (baryon)
Long ago
Rutherford (1919, named 1920)
The nucleus of H.
Neutron n
composite (baryon)
Ernest Rutherford (c.1918)
James Chadwick (1932)
Paul Dirac (1928)
Carl Anderson (e+, 1932) Now explained with
CPT symmetry.
Hideki Yukawa (1935)
César Lattes, Giuseppe Occhialini (1947) and
Cecil Powell
Explains the nuclear
force between
nucleons. The first
meson (by modern
definition) to be
discovered.
Antiparticles
Pions π
composite (mesons)
The second nucleon.
Particle
Composition
Theorized
Discovered
Comments
Muon μ−
elementary (lepton)
never
Carl D. Anderson (1936)
The first named
meson; today
considered a lepton.
Kaons K
composite (mesons)
never
1947
Discovered in cosmic
rays. The first strange
particle.
Lambda Λ
composite (baryon)
never
U Melbourne (Λ0, 1950)
The first hyperon
discovered.
Neutrino ν
elementary (lepton)
Pauli (1930), named by Fermi
C. Cowan, F. Reines (νe, 1956)
Solved the problem of
energy spectrum of
beta decay.
Q’s (uds)
elementary
Murray Gell-Mann
George Zweig (1964)
charm Q c
elementary (quark)
1970
1974
bottom Q b
elementary (quark)
1973
1977
W+/- Z
elementary (quantum)
Glashow, Weinberg, Salam (1968)
CERN (1983)
Properties verified
through the 1990s.
top Q t
elementary (quark)
1973
1995
Not found in hadrons,
but is necessary to
complete the S M
No particular
confirmation event for
the quark model.
Particle
Composition
Theorized
Discovered
Comments
Higgs boson elementary (quantum)
Peter Higgs et al. (1964)
CERN (2012)
Thought to be
confirmed in 2013.
More evidence 2014
Tetraquark
composite
?
Zc(3900), 2013 to be conf A new class of hadron
Graviton
elementary (quantum)
Albert Einstein (1916)
Not discovered
monopole
elementary (unclassified) Paul Dirac (1931)
Not discovered
Interpretation of a
grav wave as a
particle is
controversial
u
ü
Mesons
(neutral Pion)
Hadrons
u
u d
Baryons
(proton)
Incredibly, all the mesons
and baryons we find can be
constructed with the 6 quarks
and their anti-quarks in the
Standard Model. No single
quarks have ever been seen –
they seem to exist only in
At about the same time that these new particles were
being discovered, two new forces were also found.
To see how it all fits together, lets take a step
backwards…
Newton found that the force of gravity was given by:
m1m2
Fg  G 2
r
Later, people noticed that the force acting on one charged particle
from another was given by:
q1q2
Fe  k 2
r
The only two forces known at the time were very similar!
m1m2
Fg  G 2
r
q1q2
Fe  k 2
r
G and k are simply constants that scale the force and mass seems to do
the same thing in the gravity equation as electric charge in the
electromagnetic equation (except we don’t see negative mass). This
led people to think that perhaps all forces could be put in the same
framework and the formulas etc. would all be the same…
Unfortunately – the weak and strong nuclear forces – found with the
new particles, were completely different.
The strong force has a range of about 10-15 meters and is about 100
times as strong as the electromagnetic force (out to that length). The
strong force holds protons together in the nucleus of an atom.
The weak force is also very short-ranged 10-18 meters – about 0.1% of
the diameter of a proton. It is also much weaker than the strong force
(about one millionth). The weak force keeps a neutron from decaying
into a proton and an electron…
proton
Strong force
10-15
Electromagnetic
force
Weak force
Gravity
Field Theory
Remember what the gravitational field was?
We rearranged the law of universal gravitation and got:
m1m2  m1 
Fg  G 2  G 2  m2
r
 r 
Fg  [ g ]m2
where g is the gravitational field – maybe this is the way to go…
Field Theory
This is similar to:
FE  [ E ]q1
Fg  [ g ]m2
And:
FB  v  [ B ]q1
E,B, and g are the Electric, Magnetic, and Gravitational fields and the
sources of the fields are charge, moving charge, and mass
(respectively)
The old picture of what happens is the field representation – action at
a distance. The fields, like gravity are generated by something (mass)
and affect us at the speed of light. We wander through unseen fields
which push us in one direction or another.
Modern physicists use a different model to account for the action at a
distance – the exchange of an intermediate, force-carrying, virtual
particle.
These virtual particles are called
Intermediate Vector Bosons (IVB).
If the force has infinite range (like gravity and electromagnetism) the
IVB has to be massless. If a force has a finite range then the IVB must
have a mass which is actually given by the range of the force! Since the
theory makes these predictions we can look for the IVBs of each of the
known 4 forces.
Force
IVB
mass? Group
Gravity
graviton
massless
Electromagnetism
photon massless
U(1)
Weak
W+/-, Z > 80 GeV
SU(2)
Strong
gluon
>>>
SU(3)
The large Hadron
Collider – based on the
collider philosophy:
+
=
+
The ‘fear’ with the LHC is that you may force two
massive particles together with enough force to create
a singularity!
Fortunately, Black holes evaporate!
Virtual particles that appear in pairs near a event horizon
may not be able to mutually annihilate each other if only
one manages to survive a trip along the event horizon.
This process draws energy out of the black hole causing it
to evaporate. The time it takes depends only on its mass:
2560  2Gm   m 
t
 2   
3  c  h
17
3
t  3 10 m  s 
2
2
a black hole that lives for only a second has a mass of ~2 x
105 kg
Since the collision of two protons will yield much less
mass in a black hole – these will evaporate almost
instantaneously – so the Earth is saved.
(Also, much
higher energy
collisions happen
every year and we
are still here…)
If we look at the vast array of different particles we start to see some pretty
startling similarities. The Standard Model was put together to explain those
similarities.
The model explains what the world is and what holds it together. It is a simple and
comprehensive theory that explains all the hundreds of particles and complex
interactions with only:
•6 quarks.
•6 leptons. (The best-known lepton is the electron)
•4 Force carrier particles, the IVB
The Standard Model is a pretty good theory. Experiments have verified its
predictions to incredible precision, and all the particles predicted by this theory
have been found. But it does not explain everything. For example; gravity is not
included in the Standard Model; there have to be about ~20 physical constants
which have to be tuned to amazing precision; and there is no method (or reason)
to make the masses we observe.
Generation I
II
III
u
c
t
d
s
b
Quarks
Leptons
e   
e  
Charge
2
3
1

3
0
1