Drake equation

A mathematical expression, formulated by Frank Drake in 1961, which gives the number of potentially detectable civilizations in space (beyond the solar system) as the product of several distinct factors. Drake originally wrote his expression in the form: N = R fp ne fl fi fc L where Nis the number of detectable civilizations, R is the rate of star formation, fp is the fraction of stars forming planetary systems, ne is the number of planets hospitable to life, fl is the fraction of those planets where life actually emerges, fi is the fraction of planets where life evolves into intelligent civilizations, fc is the fraction of planets with intelligent beings capable of interstellar communication and L is the length of time that such a civilization remains detectable.