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Announcements
•Don’t forget about your project.
Presentations will be next Monday May 1 at
3:20pm. A written paper is also due at the
same time. Exam 4 is after the presentations
•Last exam will cover from Chapter 9
Rotating Black Holes through Chapter 13. All
essay exam…pick five from a list of eight to
ten. Exam 4 samples have been updated to
include Chapter 13
After Inflation, the strong nuclear
force “freezes out” and the universe
enters the Quark Epoch
The universe is now
a quark-gluon
plasma. The quarks
were created in the
Unified Era and
move around almost
unbound during the
Quark Era
Gluons are the exchange particles
that bind quarks together
During the Quark Epoch there were
three forces
The strong force governs quarks and gluons, the electroweak
force governs charges and leptons as well as exotic particles
and gravity governs the large scale structure of the universe.
The Electroweak Force won
Weinberg, Salam and Glashow the
Nobel Prize in Physics in 1979
James Clerk Maxwell unified
the Electric force with the
Magnetic force into the
Electromagnetic force.
Glashow, Salam and
Weinberg unified the
Electromagnetic force with
the Weak force into the
Electroweak force
For a while the quarks still roamed
free but that eventually changed
Quark-Gluon Plasma
Quarks confined into hadrons
Finally, the temperature cools to
1015 degrees and the Weak force
“freezes out”
At this point, the universe
enters the Lepton Epoch
As the temperature decreased only
electrons were left
The heavier
muon and tau
particles stopped
being created
because there
wasn’t enough
energy density to
produce them
Once the temperature fell to 1010
degrees certain reactions resulted
in more protons than neutrons
  p e n

 ne  p

Because the neutron is more massive, the reaction that
creates it is less likely than the one that creates a proton
When the temperature falls to a
billion Kelvin nucleosynthesis begins
n p  d 
The first step forms deuterium, a heavy isotope of
hydrogen. At first the deuterons are broken up by the
high energy gamma rays. Once the temperature cools
enough they can survive long enough for the next step.
H-H and D-H fusion starts to
produce 4He
Once 4He is made other fusions
occur for a short while
4
He  He  Li  
4
He  He  Be  
7
Be  e  Li  
3
7
3
7

7
Since 7Li is easily destroyed, the abundance of
this isotope in the universe gives us fundamental
information about this period of time
The relative abundance of certain
isotopes restricts the baryon matter
density of the universe
The best current
estimates say the
baryonic matter
density is only
0.04 times the
critical density
For several hundred thousand years
after the end of nucleosynthesis the
universe was a plasma
The plasma was
denser than the
surface of the sun so
it was opaque to light
Finally, the density of mass became
equal to the density of energy
Once matter became dominate the
next important event was
Recombination
After Recombination matter started
to clump together
Watch Cosmic Evolution WMAP video
Measuring the Universe
What parameters do we
measure?
H0: current value of the Hubble “constant”
k: curvature parameter
WM: mass/energy density parameter
WDM: dark matter density parameter
WL: cosmological constant parameter
q0: deceleration parameter
Determining these parameters will determine
which model best fits the universe
Measuring H0
Simple enough: measure the recessional velocity and
distance to a bunch of galaxies and plot the data on a
Hubble plot…the slope equals H0
Measuring H is a little more
complicated
Shape factor and
mass density
affect H,
especially when
you get to large Z