Inhomogeneous cosmology
Encyclopedia
Inhomogeneous cosmology usually means the study of structure in the universe by means of exact solutions of Einstein's field equations (i.e. metrics
). Such models are not homogeneous, but contain enough matter to be possible cosmological models
, or models of cosmological structures such as voids or galaxy clusters.
The best known example of such solutions is the Lemaitre-Tolman metric
(or LT model). Some other examples are the Szekeres metric, Szafron metric, Stephani metric, Kantowski-Sachs metric, Barnes metric, Kustaanheimo-Qvist metric, Senovilla metric.
(In contrast, perturbation theory, which deals with small perturbations from e.g. a homogeneous metric, only holds as long as the perturabtions are not too large, and N-body simulations use Newtonian gravity which is only a good approximation when speeds are low and gravitational fields are weak.)
Metric tensor (general relativity)
In general relativity, the metric tensor is the fundamental object of study. It may loosely be thought of as a generalization of the gravitational field familiar from Newtonian gravitation...
). Such models are not homogeneous, but contain enough matter to be possible cosmological models
Physical cosmology
Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...
, or models of cosmological structures such as voids or galaxy clusters.
The best known example of such solutions is the Lemaitre-Tolman metric
Lemaitre-Tolman metric
The Lemaître–Tolman metric is the spherically symmetric dust solution of Einstein's field equations was first found by Lemaître in 1933 and then Tolman in 1934. It was later investigated by Bondi in 1947. This solution describes a spherical cloud of dust that is expanding or collapsing under...
(or LT model). Some other examples are the Szekeres metric, Szafron metric, Stephani metric, Kantowski-Sachs metric, Barnes metric, Kustaanheimo-Qvist metric, Senovilla metric.
(In contrast, perturbation theory, which deals with small perturbations from e.g. a homogeneous metric, only holds as long as the perturabtions are not too large, and N-body simulations use Newtonian gravity which is only a good approximation when speeds are low and gravitational fields are weak.)