1
Q
Thermal History of the Universe
A
- Started very hot and dense
- Expanding ever since -> steady decrease of temperature (T) and density (ρ)
2
Q
Reactions in Thermodynamic Equilibrium
A
- Rates for forward and backward reactions are equal
- Reaction rate (Γ) faster than expansion rate (H)
3
Q
Equilibrium Condition
A
Γ ≫ H - Reaction rate is much faster than the expansion rate.
4
Q
Non-Equilibrium Condition
A
Γ ≪ H - Reaction rate is much slower than the expansion rate.
5
Q
Pair Production and Annihilation (Photons)
A
- Photon pairs can create matter and anti-matter particle pairs
- Photon energy must exceed the rest mass energy of the particle
6
Q
Early Universe Epochs (in order)
A
- Quark
- Hadron
- Lepton
- Big Bang Nucleosynthesis
- Photon
- Dark Ages
Quickly, Harry’s Little Beagle Photographed Distant Asteroids
7
Q
Quark Epoch
A
- Time: < 10-6 seconds
- Quark-gluon plasma existed
- Energies too high for hadron fromation
8
Q
Hadron Epoch
A
- Time: 10-6-1 seconds
- Quarks are bound into hadrons
- Only stable hadrons like protons and neutrons survive
9
Q
Lepton Epoch
A
- Time: 1-10 seconds
- Composition: interacting matter mostly Leptons
- Most leptons eventually annihilate
10
Q
Big Bang Nucleosynthesis
A
- Time: 10 - 1’000 seconds
- Composition: Proton-neutron equilibrium
- Helium synthesis takes place: observed H/He ratio of approximately 10
11
Q
Photon Epoch
A
- Time: 1’000 seconds - 380,000 years
- Composition: plasma in thermodynamic equilibrium
- Epoch ended with
– Formation of atoms
– Universe becoming transparent
– Release of the CMB
12
Q
Dark Ages
A
- Time: 380,000 - 108 years
- Composition cold, neutral H and He gas
- End of era marked by formation of the first stars
