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Astronomy and astrophysics Definition

Physical cosmology

Builds on Cosmological principleFriedmann–Lemaître–Robertson–Walker metricFriedmann equationsCosmological perturbation theory

Definition

Physical cosmology is the part of astrophysics whose object of study is the universe as a whole, on scales much larger than galaxies. Its models have three parts.

  1. A background spacetime that obeys the cosmological principle: the Friedmann–Lemaître–Robertson–Walker metric, whose scale factor evolves by the Friedmann equations for given matter and energy contents.
  2. Small deviations from homogeneity and their growth, described by cosmological perturbation theory and, in the nonlinear regime, by simulations.
  3. The physics of the contents, such as nuclear reactions, radiation and atoms, in this expanding background, which predicts observable quantities.

Remarks

Example: the prediction of the abundance of helium from nuclear reactions in the first minutes is a question of physical cosmology. It uses all three parts.

Non-example: the structure of a single star does not belong to physical cosmology; it does not depend on the expansion or on the large-scale state of the universe.

The current standard model of physical cosmology is the Λ\LambdaCDM model, with a cosmological constant, cold dark matter, ordinary matter and radiation.

Reading path

To understand this page from the ground up, read these 11 pages in order. The foundations come first.

Show the path as a graph
Cosmological constant, concept, no evidence levelCosmological constantconceptCosmological perturbation theory, concept, no evidence levelCosmological perturba…conceptCosmological principle, concept, no evidence levelCosmological principleconceptEinstein field equations, concept, no evidence levelEinstein field equati…conceptPerfect fluid, concept, no evidence levelPerfect fluidconceptScale factor, concept, no evidence levelScale factorconceptSpace form, concept, no evidence levelSpace formconceptSpacetime, concept, no evidence levelSpacetimeconceptFriedmann–Lemaître–Robertson–Walker metric, example, no evidence levelFriedmann–Lemaître–Ro…exampleFriedmann equations, statement, no evidence levelFriedmann equationsstatementPhysical cosmology, definition, no evidence levelPhysical cosmologydefinition
Each page uses the pages above it. The colour of the bar on a box shows how strong the evidence is, and the box also gives it as text. The list has the same pages.
  • no evidence level
  1. Cosmological constant concept
  2. Cosmological perturbation theory concept
  3. Cosmological principle concept
  4. Einstein field equations concept
  5. Perfect fluid concept
  6. Scale factor concept
  7. Space form concept
  8. Spacetime concept
  9. Friedmann–Lemaître–Robertson–Walker metric example
  10. Friedmann equations statement
  11. Physical cosmology definition

Further reading

  1. Web https://en.wikipedia.org/wiki/Physical_cosmology
About this page
TagE2HR63CT8P
URIm2://E2HR63CT8P
Kinddefinition
WritingW0 stub
MSC85A40, 83F05
DefinesPhysical cosmology
UsesCosmological principle, Friedmann–Lemaître–Robertson–Walker metric, Friedmann equations, Cosmological perturbation theory
Changed3 November 2026

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