cosmology, field of study that brings together the natural sciences, particularly astronomy and physics, in a joint effort to understand the physical universe as a unified whole.
The “observable universe” is the region of space that humans can actually or theoretically observe with the aid of technology..
Research in cosmology involves astronomy, but also gravitational physics, particle physics, and challenging questions about the interpretation of phenomena we can't see directly — such as the possible existence of something before the Big Bang..
Quantum cosmology then refers to the quantization of a restricted set of the degrees of freedom allowed in quantum gravity.
The geometries commonly encountered in (classical) cosmology like Robertson-Walker, de Sitter, and mixmaster universes are only the homogeneous anisotropic solutions to Einstein's equations.
After introducing the equilibrium distributions for different particles, we perform an inventory of the constituents of the universe:
