Drake equation
probabilistic argument to estimate the number of alien civilizations in the galaxy / From Wikipedia, the free encyclopedia
In 1961, Frank Drake wrote down an equation for the chance of a contactable alien civilization from another planet in the Milky Way Galaxy. This is known as the Drake Equation (sometimes called the Green Bank equation or the Green Bank Formula). Carl Sagan mentioned the Drake equation so often that it has been mistaken for the 'Sagan equation'.