The most famous American astronomer and astrophysicist Carl Sagan explains the Drake equation.
The Drake equation (rarely also called the Green Bank equation or the Sagan equation) is a famous result in the speculative fields of xenobiology, astrosociobiology and the search for extraterrestrial intelligence.
The Drake equation states that:
N = R* × fp × ne × fl × fi × fc × L, where:
N is the number of civilizations in our galaxy, with which we might hope to be able to communicate;
R* is the rate of star formation in our galaxy
fp is the fraction of those stars that have planets
ne is the average number of planets that can potentially support life per star that has planets
fl is the fraction of the above that actually go on to develop life at some point
fi is the fraction of the above that actually go on to develop intelligent life
fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L is the length of time such civilizations release detectable signals into space.
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