The Cosmological Constant
arXiv:1211.6337
Abstract
Contrary to popular mythology, Einstein did not invent the cosmological constant just in order construct his model universe. He discussed it earlier in "The Foundations of General Relativity" in connection with the proper structure of the source-free field equations. There he dismissed it as arbitrary and unnecessary. It was later that he found its inclusion to be essential to the construction of his model.
3 pages