Review for
the Midterm
What to really know and what are the key concepts?
Historical Cosmologies:
- Progression from Discovery to Hierarchy
- Magic Universe - Life confronting Life
- Mythic Universe - personality driven
- Geometric Universe - relative motion observed and described;
calendars built
Original Ideas:
- Cosmic Womb
- Earth, Air, Fire and Water
- Universe runs by itself
- Relativity
- Homogeneity
- Gravity is a long range attractive force
-
- Curved spacetime is gravity
Models of the Solar System and the Players:
Now on to the Universe:
Two Key Observations:
- Galaxy redshifts --> redshift correlates with distance implying
an expanding uniform surface
- Microwave background --> uiverse is filled with photons at some
characteristic temparture
The above two observations mean that the universe evolves from a hot,
high density state to a cold low density state
Thermal History of the Universe:
- Universe has a unique temperature at any given expansion time
or radius
- Particle creation (matter+anti-matter) from the radiation field
since
- Quantum mechanics and the uncertainty principle demands that
at, early times, there are large energy fluctuations (birth of the
Universe?)
- Photon energy distribution and particle creation:
- This means there are windows of creation for different particles
depending on their mass
- Observed ratio of photons to baryons is 1 billion to 1 -->
this represents a tiny assymmetry in the amount of matter relative
to anti-matter
- Important Thermal Epochs
- Free Quark Era
- Electroweak symmetry breaking
- Proton and Neutron creation windows
- neutrino interactions to keep number of protons and neutrons
equal
- neutrino decoupling
- closing of electron creation window
- annihilation of electron-positron pairs
- formation of helium to prevent neutron decay
Radiation Dominated Era:
- matter is ionized
- scattering of photons by free electrons couples radiation
and matter
- radiation pressure/momentum tries to smooth out the distribution
of matter (gravity is unimportant)
- how did galaxies form under these conditions?
- At 100,000 years, the universe cools to 3000 degrees and the
electrons recombine with protons
- Matter is no longer ionized and the radiation escapes - we
see this epoch as the surface of last scattering and it is now redshifted
to microwaves - this is the MWB!
- Gravity can now work to clump matter and build structure around
pre-existing density fluctuations (but how?).
return
___________________________________________________________________
The Electronic Universe Project
e-mail: nuts@moo.uoregon.edu
means that photons must follow the
curvature of the universe
