Cosmological Principle
We do not occupy a preferred place in the Universe (Copernican belief)
and further, that at a given time, the Universe
appears homogeneous and isotropic to all
observers
Homogeneity and Isotropy of the Universe
- homogeneous and isotropic
- homogeneous
The question of the homogeneity and isotropy of the Universe
cannot be answered until one
specifies the size of the region which should be averaged over. For
example, the Solar System is clearly inhomogeneous; there is a star at
the center of the system which is surrounded by objects. The Solar System
looks differently depending upon where you look. The
scale upon
which the Universe should appear homogeneous and isotropic is not
well-defined, outside of the requirement that it is large.
The homogeneous and isotropic assumptions are tough. Recall that the
CMBR is homogeneous and isotropic but that regions in the
Universe which are in opposite directions are
not causally connected and so really have no
reason why they should have the same properties.
Why?
This is known as the Horizon Problem