File:Cosmic expansion visual.gif

English: Top Row: A visualization of a pulse of light, represented by the circle, as observed at rest with respect to the expanding universe. The radius of the light pulse grows linearly with the speed of light. The rate of cosmological expansion is shown by the moving gridlines. The dotted grid marks the original location of the grid in space prior to expansion. On the left hand side is a representation of this expansion and the consequential observation of the light pulse, given the assumption that the universe is dominated by radiation. This expansion rate is proportional to t^(1/2). Similarly, on the right is a visual reprentation of the same light pulse, as viewed by a static observer in a matter dominated universe. In this case the universal expansion is proportional to t^(2/3).

Bottom Row: A visualization of a pulse of light as viewed by a comoving observer, i.e. an observer moving with the Hubble Flow/cosmological expansion. Notice that the gridlines appear static, since the perspective of the comoving observer moves with the expansion. On the left, the light pulse expands at the speed of light, just as in the top row. On the left hand side, the effects of an expanding universe dominated by radiation is shown. Similarly on the right, the observation of the light pulse is shown from the same perspective, but assuming a matter dominated universe.

This animation was created by cosmology graduate students from the Astronomy Department at the University of Illinois at Urbana-Champaign.