Suggested reading: Longair "Galaxy Formation" Sections 1.1 - 1.3
How n:p ratio determines fraction of 4He
Measurement of primordial He abundance
Why do no elements like carbon get made?
Nuclear reaction network: note problem at B, Be and Li with mass 8.
What controls abundances of 3He, D and Li?
Baryon density and ratio to photon density
Observational tests of BBN predictions
Measuring the primordial deuterium abundance
Absorption lines in QSO spectra: note "Ly alpha forest"
Measurement of H abundance using damping wings on H line
Detecting higher-order D lines (a very small wavelength shift from H lines)
Detailed fits of D and H lines
Final measurement of D abundance
Measurements from different QSO absorbers
Comparison with predictions: it works really well!
Implications: Big Bang theory works; there is lots of non-baryonic dark matter
History: use of galaxy clusters to show that Omega_matter can't be 1
Count (luminous) baryons in rich cluster
If clusters are representative of the universe, we have a contradiction
Lambda came to the rescue a few years later
