**Cosmological Constant; Lambda**

A constant term (labeled Lambda) which Einstein added to his general theory of
relativity in the mistaken belief that the Universe was neither expanding nor
contracting. The cosmological constant was found to be unnecessary once
observations indicated the Universe was expanding. Had Einstein believed what
his equations were telling him, he could have claimed the expansion of the
Universe as perhaps the greatest and most convincing prediction of general
relativity; he called this the "greatest blunder of my life".

In physical
cosmology,
the

**cosmological constant**(usually denoted by the Greek capital letter lambda: Λ) is equivalent to an energy density in otherwise empty space. It was originally proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. Einstein abandoned the concept after the observation of the Hubble redshift indicated that the universe might not be stationary, as he had based his theory on the idea that the universe is unchanging. However, a number of observations including the discovery of cosmic acceleration in 1998 have revived the cosmological constant, and the current standard model of cosmology includes this term.
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