### Why ET Hasn’t Called

##### The lifetime of civilizations in the Drake equation

for estimating extraterrestrial ntelligences

is greatly exaggerated

In science there is arguably no more suppositional formula than that proposed in 1961 by radio astronomer Frank Drake for estimating the number of technological civilizations that reside in our galaxy: *N = R fp ne fl fi fc L*

In this equation, *N* is the number of communicative civilizations, *R* is the rate of formation of suitable stars, *fp* is the fraction of those stars with planets, *ne* is the number of Earth-like planets per solar system, *fl* is the fraction of planets with life, *fi* is the fraction of planets with intelligent life, *fc* is the fraction of planets with communicating technology, and *L* is the lifetime of communicating civilizations. (continue reading…)