For the existence of extraterrestrial civilizations
N = R* x fp x ne x fl x fi x fc x L
N = The number of civilizations in the Milky Way Galaxy whose electromagnetic emissions are detectable.
R* = The rate of formation of stars suitable for the development of intelligent life.
fp = The fraction of those stars with planetary systems.
ne = The number of planets, per solar system, with an environment suitable for life.
fl = The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges.
fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = The length of time such civilizations release detectable signals into space.
There are an estimated 200 – 400 billion stars exist within our Milky Way, and modern estimates say that there between 1.65 ± 0.19 and 3 new star form every year.