# cosmological constant

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## cosmological constant

(koz-mŏ-**loj**-ă-kăl) A constant term that can be added to Einstein's field equations of general relativity theory. The cosmological constant was originally put forward by Albert Einstein in 1917 to ensure that the application of general relativity theory to the Universe results in a static Universe rather than an expanding or contracting Universe. The discovery that the Universe is expanding removed the necessity for introducing the cosmological constant but cosmological models with a nonzero cosmological constant have been considered by theoreticians.

For many years it was thought that the value of the cosmological constant is exactly zero but, starting in the late 1990s, evidence began to accumulate that the cosmological constant has a small but nonzero value. This has the consequence that the expansion of the Universe is accelerating. There have been many attempts to show why the value of the cosmological constant is either zero or very small but there is no consensus as to why this should be the case.

## Cosmological Constant

the constant A introduced by A. Einstein in 1917 into his equations of gravitation (1916) so that these equations would have solutions describing a static universe and would satisfy the requirement of the relativity of inertia. The physical meaning of the introduction of the constant consists in the assumed existence of special cosmic forces (of repulsion at ∧ > 0 and of attraction at ∧ < 0) that increase with distance. Since the requirement of a static universe became redundant with the discovery that galaxies are receding from one another, Einstein abandoned the cosmological constant in 1931. From this time on, it was assumed that ∧ ≡ 0. Another possibility is being considered at present (the 1970’s), namely, that the cosmological constant is extremely small (∽10^{−55} cm^{−2}).

### REFERENCE

Zel’dovich, la. B., and I. D. Novikov.*Reliativistskaia astrofizika*. Moscow, 1967.

G. I. NAAN