Transcript: The big bang model cannot be properly described without a measurement of the dark matter density in the universe. Observations of individual galaxies, either their rotation curves or velocity dispersions, and observations of clusters of galaxies show that ninety to ninety-five percent of the matter in the universe is dark. We don’t yet know what it is, but it’s almost certainly in the form of microscopic particles not yet detected in labs on the Earth. A variety of techniques are used by astronomers to measure dark matter on different scales. They show that galaxies are imbedded in dark matter, that there’s a large amount of dark matter in clusters, and that even in the space between galaxies there is dark matter. The cosmic density of dark matter with the current best measurements is about thirty percent of the critical density; omega equals 0.3. Even with the baryonic material added, dark matter does not have sufficient density to close the universe or overcome the cosmic expansion.