The Drake equation was written in 1961 by astrophysicist Frank Drake to estimate the number of intelligent civilizations in the Milky Way galaxy. The equation summarizes the main concepts which scientists must contemplate when considering the question of other communicative life.
The Drake equation is: # = R x P x L x D x C x S x T
# = the number of civilizations in our galaxy with which communication might be possible
R = the average Rate of star formation in our galaxy
P = the fraction of those stars that have Planets
L = the average number of planets that can potentially support Life per star that has planets
D = the fraction of planets that could support life that actually Develop life at some point
C = the fraction of planets with life that actually go on to develop Civilizations
S = the fraction of civilizations that develop a technology that releases detectable Signs of their existence into space
T = the length of Time for which such civilizations release detectable signals into space
The ‘educated guesses’ used by Drake and his colleagues in 1961 were:
R = 1 (1 star formed per year, on the average over the life of the galaxy)
P = 0.2 to 0.5 (one fifth to one half of all stars formed will have planets)
L = 1 to 5 (stars with planets will have between 1 and 5 planets capable of developing life)
D = 1 (100% of these planets will develop life)
C = 1 (100% of which will develop intelligent life)
S = 0.1 to 0.2 (10–20% of which will be able to communicate)
T = 1000 to 100,000,000 (which will last between 1000 and 100,000,000 years)
Inserting the above minimum numbers into the equation gives a minimum of 20 civilizations.
Inserting the maximum numbers gives a maximum of 50,000,000.
Drake’s original meeting concluded that there were probably between 1000 and 100,000,000 civilizations in the galaxy.
The Drake equation can give a very wide range of values, depending on the assumptions, as the values used by Drake are not well established. The result can be # ≪ 1, meaning we are likely alone in the galaxy, or # ≫ 1, implying there are many civilizations. The presence of humanity implies a probability of intelligence arising of greater than zero. (Assuming that humanity is actually intelligent).