| Astrophysics (Index) | About |
The cosmological principle is that on a large enough scale, there is no particular place or direction in the universe: in any direction and at any (long) distance you find the same amount of matter, i.e., the distribution of matter is homogeneous and isotropic when viewed at a sufficiently large scale.
A consequence is a size-limit of large scale structures within the universe: given any two points (at any given time) within the universe between which light has not had sufficient time to travel within their age of the universe, the relationship between what is at each point must be random, i.e., a single structure spanning them both could not be created other than by pure coincidence. Announcements of patterns (indicating structures) discerned in the universe that exceed such a size invariably lead to debate and challenge.
I've seen the cosmological principle stated to be "the laws of physics are the same everywhere" (I would put this as "there exists a set of laws of all physics that apply everywhere"). This has also been stated to be a consequence of the cosmological principle.