Thamarai's Blog

Cral Sagan stated that we define an advanced civilization as one capable of radio astronomy, but that this is a parochial definition because there could be countless worlds on which the inhabitants are accomplished linguists or superb poets but indifferent radio astronomers, so we will not hear from them. Following the lead, he presented the equation created by Frank Drake of Cornell University, which tries to derive an estimation of N, the possible number of advanced technical civilizations in the galaxy. Here it is, Sagan - Drake Formula :

N = N_* x f_p x n_e x f_l x f_i x f_c x f_L

where

N_* is the number of stars in the MilkyWay Galaxy;

f_p is the fraction of stars that have planetary systems;

n_e is the number of planets in a given system that are ecologically suitable for life;

f_l is the fraction of otherwise suitable planets on which life actually arises;

f_i is the fraction of inhabited planets on which an intelligent form of life evolves;

f_c is the fraction of planets inhabited by intelligent beings on which a communicative technical civilization develops;

f_L is the fraction of a planetary lifetime graced by a technical civilization.