An Etymological Dictionary of Astronomy and Astrophysics

A solution to → Einstein’s field equations of → general relativity which contains no ordinary matter (Ω_M = 0) or radiation (Ω_R = 0), is → Euclidean (k = 0), but has a → cosmological constant (Ω_Λ > 0). The Universe expands exponentially forever. This solution was the first model expanding of → expanding Universe. See also → empty Universe, → Milne Universe.

See also: After the Dutch mathematician and physicist Willem de Sitter (1872-1934) who worked out the model in 1917; → universe.