The Cosmological Principle
Considering the largest
scales in the universe, we make the following fundamental assumptions:
1) Homogeneity: On the
largest scales, the local universe has the same physical
properties throughout the universe.
Every region has the same physical properties (mass density, expansion rate, visible vs. dark matter, etc.)
2) Isotropy: On the
largest scales, the local universe looks the same in any direction
that one observes.
You should see the same large-scale structure in any direction.
3) Universality: The
laws of physics are the same everywhere in the universe.
