The above cube represents a chunk of our universe as simulated by the Grand Challenge Cosmology Consortium (GC3). The cube is huge - it would take light 500 million years to cross it. Low density gas is shown as blue, and high density gas as red. In the beginning of the universe, matter and gas were spread quite uniformly. As this computer universe evolved, gravity caused high density areas to be created. This simulation hypothesized that 1/3 of the universe is composed of slow moving "cold dark matter", and 2/3 composed of fast moving "hot dark matter." The areas of high and low density resulting from this computer simulation are similar to those observed by astronomers in the real universe.