© Courtesy of V. Springel, Max-Planck-Institute for Astrophysics, Germany.
Large structures formed as small density fluctuations in the early universe collapsed under the influence of gravity. Here, we see three different stages of structure formation in a computer simulation starting on the left with 10 billion particles almost uniformly distributed in space. The center box shows an intermediate stage in the evolution of the universe, and the rightmost box shows the universe at the present time, with filaments and clusters of galaxies strung out in space. (Unit: 4)