Cosmological principle

Under the cosmological principle ( or cosmological postulate ) are two basic assumptions summarized in the scientific cosmology, which are their models of the universe as a whole is based. It is closely linked with the Copernican principle. The cosmological principle was introduced in 1933 by the astrophysicist Edward A. Milne.

• The universe is homogeneous - that is, it raises an observer regardless of the point of the room in which it is located, is always the same (principle of homogeneity, also known as the Copernican principle).
• The universe is isotropic - that is, it appears to the observer regardless of the direction of observation in space is always the same (principle of isotropy ).

A stronger version of the cosmological principle, the so-called perfect cosmological principle requires, beyond the spatial, temporal homogeneity. This version, initially assisted by representatives of steady-state cosmologies such as Hermann Bondi and Fred Hoyle, today plays only a minor role.

Since the matter in the universe to " short distances " is not evenly distributed, these assumptions are valid only under the condition that you look at areas of such an extent, that is distributed in this matter on average equal.

However, the cosmological principle leads to the assumption of some cosmologies olbersschen paradox, so that it is consistent only with certain cosmologies, such as the Big Bang theory.