N = R* x fp x ne x fl x fi x fc x L
I like Drake's equation a lot.
makes me imagine a lot of different worlds ...
I report the explanation from wiki
The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.
where:
N = the number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light
cone);
and
R∗ = the average rate of star formation in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of planets that could support life that actually develop life at some point
fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space[5][6]