Topics to Investigate: Observational Constraints

• H₀ from direct measurements (e.g., HSTKP)
• q₀ from type Ia supernovae (e.g., Hi-z; SCP)
• Age constraints [f(q₀,1/H₀)] from globular clusters (e.g., VSB)
• Ω_b from deuterium & other light element abundances (e.g., Olive; TOSL)
• Ω_m from
  • kinematics
  • large scale structure (e.g., 2dF; 2dF-lite, and many, many SDSS works)
  • cluster baryon fractions (e.g., Evrard)
  • cluster mass-to-light ratios (e.g., BCDO; CNOC)
    SHF combine several of these
• Ω_Λ from gravitational lensing statistics (e.g., CQM; K)
• Ω_m + Ω_Λ from the cosmic microwave background (e.g., WMAP) and baryon acoustic oscillations.
• See the more general list of topics for more ideas.

Also see the extended reference list for further pointers.

A brief discussion combining many of these topics is given by
The Observational Case for a Low Density Universe with a Non-Zero Cosmological Constant
Ostriker & Steinhardt 1995, Nature, 377, 600
I will lead a discussion of this paper to launch our more detailed discussion of the individual observational constraints.

Note that many of the observational constraints often boil down to a statement like "Ω_bh² = 0.019 +/- 0.001." This is the essence of what you're after, though of course you need to understand the method in order to appreciate how the result is obtained and what might go wrong. But we will need something like this as a bottom-line answer for intercomparison of results in the culminating debate.

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