My beef with the Drake Equation

I’ve got some issues with the Drake Equation.

For those of you who aren’t familiar with it, the Drake Equation is a mathematical statement designed to estimate the number of detectable intelligent civilisations in our galaxy. It was devised in 1961 by Frank Drake, Emeritus Professor of Astronomy and Astrophysics at the University of California, and it assumes the following form:

N = R* • fp • ne • fl • fi • fc • 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.

When Drake first proposed the equation, he and his colleagues calculated that there were ten intelligent civilisations in the Milky Way at any given point in time. Since then the Drake Equation has been one of the cornerstones of speculation on extraterrestrial life, both in fiction and non-fiction.

But here’s the problem – many of its variables cannot be adequately estimated based on our current knowledge of the universe. In other words, the Drake Equation is an exercise in guessing.

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