De Sitter universe

A cosmological solution with a positive cosmological constant and no matter, in which space expands exponentially. It models the late-time behavior of universes dominated by dark energy.

Cosmological constant: A constant term in Einstein’s field equations that contributes uniform energy density to spacetime. Its positive value drives the exponential expansion of a De Sitter universe.
General relativity: A theory of gravity in which matter and energy determine spacetime curvature. De Sitter geometry is an exact solution of Einstein’s gravitational equations.
Willem de Sitter: A Dutch astronomer and physicist who developed early relativistic cosmological models. His 1917 solution gave the universe its name.
Einstein static universe: A relativistic cosmological model with constant scale factor, supported by matter and a cosmological constant. Unlike De Sitter space, it is static and contains matter.
Hubble parameter: The rate of cosmic expansion at a given time, expressed as fractional change in scale per unit time. It remains constant during ideal De Sitter expansion.
Einstein field equations: Equations relating spacetime curvature to matter, energy, and the cosmological constant. They admit De Sitter spacetime when the cosmological constant is positive and matter is absent.
Einstein–de Sitter controversy: A debate over whether Einstein’s static cosmology or de Sitter’s expanding solution described the universe. Their disagreement shaped early interpretations of the cosmological constant and cosmic expansion.
Anti-de Sitter space: A maximally symmetric spacetime with negative cosmological constant and constant negative curvature. Its negative curvature and boundary structure contrast with De Sitter space.
De Sitter horizon: A causal boundary in De Sitter spacetime beyond which events cannot send signals to a given observer. Exponential expansion gives each observer a finite cosmic horizon.
Homogeneous universe: A cosmological model whose properties are the same at every spatial location on large scales. The standard De Sitter cosmology assumes spatial homogeneity.

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