Big Bang Cosmology

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Big Bang Cosmology

• A crash course about what is important
• (and what is not)

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Our Universe Expands!
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The Universe Cools(and therefore used to be much
hotter!)
Primordial Nucleosynthesis
Cosmic Microwave Background
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The density of the Universe determines its future!
Open Universes O lt 1
Closed Universes O gt 1
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Friedmanns equation and geometry
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Photons get redshifted and run along
null-geodesics
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Most of the density of the Universe is
unseenDark Energy Dark Matter
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Simple Big Bang Models has problems.

• The Horizon problem why is our Universe so
  Homogeneous?
• The Composition problem why are there a billion
  photons for each atom?
• The Flatness problem why is O so close to unity?

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Out of particle physics comes a possible
solution Inflation

• In Inflation the Universe expands rapidly for a
  short time
• The vacuum energy needed for Inflation comes from
  some quantum scalar field.

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A Universe after Inflation..

• Is almost flat O 1 a very small number
• Has no Horizon Problem

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The concentration of stable particles in the
Universe is determined by Interaction Strength
and by Mass

• Massless particles are always as abundant as
  photons
• Weakly interacting particles (leptons) are more
  abundant than strongly interacting particles
  (quarks)
• More massive particles are less abundant than
  less massive particles
• A small asymmetry between matter and anti-matter
  is sufficient to explain the large number of
  photons per baryon

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The Concordance Modelthe sum of current
knowledge of the Universe
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