The Drake Equation

Is there a way to estimate the number of technologically advanced civilizations that might exist in our Galaxy? While working at the National Radio Astronomy Observatory in Green Bank, West Virginia, Dr. Frank Drake conceived a means to mathematically estimate the number of worlds that might harbor beings with technology sufficient to communicate across the vast gulfs of interstellar space. The Drake Equation, as it came to be known, was formulated in 1961 and is generally accepted by the scientific community.

N = R* f_p n_e f_l f_i f_c L
where,

• N = The number of communicative civilizations
• R* = The rate of formation of suitable stars (stars such as our Sun)
• f_p = The fraction of those stars with planets. (Current evidence indicates that planetary systems may be common for stars like the Sun.)
• n_e = The number of Earth-like worlds per planetary system
• f_l = The fraction of those Earth-like planets where life actually develops
• f_i = The fraction of life sites where intelligence develops
• f_c = The fraction of communicative planets (those on which electromagnetic communications technology develops)
• L = The "lifetime" of communicating civilizations

Frank Drake's own current solution to the Drake Equation estimates 10,000 communicative civilizations in the Milky Way. Dr. Drake, who serves on the SETI League's advisory board, has personally endorsed SETI's planned all-sky survey.