A constant introduced by Einstein Eric Weisstein's World of Biography (1917) into the equations of general relativity to allow a steady state cosmological solution to the Einstein field equations. The constant was introduced before the concept of the Big Bang had been conceived, so an expanding or contracting universe Eric Weisstein's World of Astronomy was regarded as physically implausible, leading Einstein to add as a "fudge factor." In theory, the constant can be derived from quantum field theory, but the derivation has not yet been performed. Einstein's cosmological constant is equivalent to a vacuum energy density, which means it can be put on the left hand side of Einstein's equations with the geometry (as Einstein did), or on the right hand side with the stress-energy, both forms being mathematically equivalent.
Generally, does not play a significant role in the early universe. Eric Weisstein's World of Astronomy
Big Bang, Cosmology, Einstein Field Equations
References
Einstein, A. "Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie." Sitzungsber. Preuss. Akad. Wiss., 142-152, 1917. Reprinted in English in Lorentz, H. A.; Einstein, A.; Minkowski, H.; and Weyl, H. The Principle of Relativity: A Collection of Original Memoirs on the Special and General Theory of Relativity. New York: Dover, 1952.
Goldsmith, D. Einstein's Greatest Blunder? The Cosmological Constant and Other Fudge Factors in the Physics of the Universe. Cambridge, MA: Harvard University Press, 1997.
Ridpath, I. (Ed.). A Dictionary of Astronomy. Oxford, England: Oxford University Press, 1998.
Weinberg, S. Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity. New York: Wiley, p. 613, 1972.
