Astrophysics (Index)About

cosmic variance

(density variation on a cosmic scale)

Cosmic variance is variation in density, mass, and populations on the largest scale, i.e., the large scale structure, which is a contributer to the statistics of surveys on the largest scale. Variation is presumed to occur on every observable scale (and presumably on scales beyond) so deep surveys of portions of the sky are presumed to be unrepresentative of the entire sky and statistics derived from the survey must admit a factor regarding the affect of this beyond mere random chance, the cosmic variance. The entire observable universe (to the surface of last scattering or particle horizon) might be affected, more dense or less dense than the "universe" beyond, but though there will be attempts to accommodate that, there are more credible means of dealing with density variations on a small enough scale to be detected in an all-sky survey or strategic samples scattered over the whole sky.

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