precision cosmology

Wayne Hu (Chicago) gave his talk today about precision cosmology. Blandford forced Hu to slow way down when he was discussing the specific assumptions that go into the determination of the distance to last scattering. Hu's discussion was absolutely great; he argued that there are very few assumptions involved, except maybe adiabaticity (which is tested, but not at the level required). He spent some additional time encouraging us to determine the Hubble Constant. He espoused some heresies including that he considered a small amount of spatial curvature much more plausible than a non-trivial equation of state for the dark energy (I agree); these are degenerate for some experiments.

In the afternoon we continued on the Hubble Constant. I spent time re-reading Eisenstein et al (2005), a paper on which I am proud to be a co-author, though I can't take credit for some of the best parts. The baryon acoustic feature in the LRG correlation function constrains strongly the distance to redshift 0.35, but less strongly the Hubble Constant, because uncertainties in the world model enter. Similarly, I realized, the lensing time delays only measure the Hubble Constant in the context of a specific world model; really each system constrains a combination of cosmological parameters. It's my job to figure that out tomorrow.