Cosmologists understand well the statistical properties of the Universe when it was a mere 380,000 years old. The COBE, WMAP, and PLANCK satellite missions have mapped out the tiny temperature fluctuations which grew from quantum seeds implanted in the first instants of the Big Bang. The Universe then was a plasma described by linear fluid equations and characterized by a small set of cosmological parameters. Comparison of linear calculation predictions to the data yields high precision constraints for many of these parameters, but significant degeneracies remain from this analysis alone.
Right: A region of synthetic sky from an N-body simulation dressed with empirical properties. The image, which includes stars and all of the expected instrumental effects (bad pixels, cosmic rays, etc), contains a distant galaxy cluster (red, circled galaxies, with squares showing the true members found in 3D) as well as numerous foreground/background objects. (Courtesy of A. Evrard)