The Drake Equation

The Drake Equation[2], often written as

$N=Rf_pn_ef_lf_if_cL$,

is a way to estimate the number of sources that SETI might detect. The purpose of the drake equation is to identify the factors that influence this number:

• $R$ is the rate at which new stars are formed
• $f_p$ is the fraction of such starts that have planets
• $n_e$ is the fraction of such planets which can support life
• $f_l$ is the fraction of such planets on which live develops
• $f_i$ is the fraction of biospheres where intelligence arises
• $f_C$ is the fraction of intelligent civilizations which develop interstellar communications
• $L$ is the length of time that such a civilizaion remains in communication