"What do we need to know about to discover life in space?"
can we estimate the number of technological civilizations that might exist
among the stars? While working as a radio astronomer at the National Radio
Astronomy Observatory in Green Bank, West Virginia, Dr. Frank Drake (now
Chairman of the Board of the SETI Institute) conceived an approach to bound
the terms involved in estimating the number of technological civilizations
that may exist in our galaxy. The Drake Equation, as it has become known,
was first presented by Drake in 1961 and identifies specific factors thought
to play a role in the development of such civilizations. Although there is
no unique solution to this equation, it is a generally accepted tool used
by the scientific community to examine these factors.
--Frank Drake, 1961
The equation is usually written:
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. For more information, please visit Dr.
William Calvin's "The Drake Equation's fi"
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.
Within the limits of our existing technology, any practical search for
distant intelligent life must necessarily be a search for some manifestation
of a distant technology. In each of its last four decadal reviews, the National
Research Council has emphasized the relevance and importance of searching
for evidence of the electromagnetic signature of distant civilizations.
Besides illuminating the factors involved in such a search, the Drake
Equation is a simple, effective tool for stimulating intellectual curiosity
about the universe around us, for helping us to understand that life as we
know it is the end product of a natural, cosmic evolution, and for making
us realize how much we are a part of that universe. A key goal of the SETI
Institute is to further high quality research that will yield additional
information related to any of the factors of this fascinating equation.