Cosmological Constant

A term (represented by the Greek letter Lambda, Λ) that Albert Einstein originally introduced into his equations of General Relativity to allow for a static, unchanging universe. He later called it his "greatest blunder" after the discovery of the universe's expansion. However, the concept was spectacularly revived with the 1998 discovery of the universe's accelerating expansion, for which the Nobel Prize was awarded in 2011. It is now the leading explanation for Dark Energy. The Cosmological Constant represents a constant energy density filling the vacuum of space homogeneously, producing a repulsive gravitational force that drives cosmic acceleration. Its incredibly small, yet non-zero, value poses the most severe fine-tuning problem in physics, known as the Cosmological Constant Problem.