The theory of inflation predicts that the density parameter Omega is equal to one. Any deviations from one at the epoch of inflation can be visualized as a slight curvature of space which gets smoothed out as the universe expands by a large factor among the inflationary epoch. One can translate the Omega parameter which measures mass density in terms of the critical value into a mass-to-light ratio by dividing the critical density by the observed luminosity density of an average (and large) volume of the universe. The result is that the mass-to-light ratio equals 1500Omega. In other words, if Omega=1, one needs a mass-to-light ratio of 1500 to close the universe, far greater than is observed. Alternatively, if we adopt the mass-to-light ratio measured on large scales of 300 as being a universal value, we would conclude that Omega=0.2. If inflation theory is correct, one can only reconcile observation and theory if the bulk of the dark matter is uniformly distributed over scales up to 10 Mpc. In this case, it would not have shown up in dynamical measurements, which only sample the clumped component of the mass density.

Joe Silk