The Drake Equation

A photograph of Frank Drake, posing in front of his equation written on a white board. Frank Drake is an American astrophysicist, most notable as one of the pioneers in the search for alien intelligence, and the creator of the Arecibo Message - a digital encoding of an astronomical and biological description of the Earth and its lifeforms for transmission into the cosmos.  Source: SETI Institute

In 1974, we humans sent a message – an interstellar communiqué, if you will – aimed at Messier 13, a globular cluster of stars, about 21,000 light-years away.

Its content was determined by astrophysicist and Search for Extra-Terrestrial Intelligence (SETI) founder Frank Drake, and visionary Carl Sagan.

Frank Drake is most notable as one of the pioneers in the search for extraterrestrial intelligence, including the founding of SETI. He mounted the first observational attempts at detecting extraterrestrial communications in 1960 in Project Ozma, and developed his famous equation.

The Drake equation is a probabilistic argument used to arrive at an estimate of the number of active, communicative extraterrestrial civilisations in the Milky Way galaxy.  The number of such civilisations, N, is assumed to be equal to the mathematical product of

(i) the average rate of star formation, R*, in our galaxy,
(ii) the fraction of formed stars, fp, that have planets,
(iii) the average number of planets per star, ne, that can potentially support life,
(iv) the fraction of those planets, fl, that actually develop life,
(v) the fraction of planets bearing life on which intelligent, civilised life, fi, has developed,
(vi) the fraction of these civilisations that have developed communications, fc, i.e., technologies that release detectable signs into space, and
(vii) the length of time, L, over which such civilisations release detectable signals, for a combined expression of:

N=R^{\ast} \cdot f_p \cdot n_e \cdot f_l \cdot f_i \cdot f_c \cdot L

Little 'Bytes' about Natural Phenomena, Theoretical Physics and the Latest Worldwide Scientific Findings. Edited from Glasgow, Scotland.