Drake equation


is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy

Related formulas


Nthe number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light cone) (dimensionless)
Rthe average number of star formation per year in our galaxy (year-1)
fpthe fraction of those stars that have planets (dimensionless)
nethe average number of planets that can potentially support life per star that has planets (dimensionless)
flthe fraction of planets that could support life that actually develop life at some point (dimensionless)
fithe fraction of planets with life that actually go on to develop intelligent life (civilizations) (dimensionless)
fcthe fraction of civilizations that develop a technology that releases detectable signs of their existence into space (dimensionless)
Lthe length of time for which such civilizations release detectable signals into space (year)