In 1961, astronomer Frank Drake set out to develop a scientific formula to calculate the number of technological civilizations that might exist in the universe. Known as the Drake Equation, the formula identifies factors that might play a role in the development of such civilizations.
The formula is expressed as:
N = R* x fp x ne x fl x fi x fc x L
N = The number of communicative civilizations
The number of civilizations in the Milky Way Galaxy whose radio emissions are detectable.
R* = The rate of formation of suitable stars
The rate of formation of stars with a large enough "habitable zone" and long enough lifetime to be suitable for the development of intelligent life.
fp = The fraction of those stars with planets
The fraction of Sun-like stars with planets is currently unknown, but evidence indicates that planetary systems may be common for stars like the Sun.
ne = The number of earthlike worlds per planetary system
All stars have a habitable zone where a planet would be able to maintain a temperature that would allow liquid water. A planet in the habitable zone could have the basic conditions for life as we know it.
fl = The fraction of those planets where life develops
Although a planet orbits in the habitable zone of a suitable star, other factors are necessary for life to arise. Thus, only a fraction of suitable planets will actually develop life.
fi = The fraction of life-bearing worlds on which intelligence develops
Life on Earth began more than 3.5 billion years ago. Intelligence took a long time to develop. On other life-bearing planets it might happen faster, it might take longer, or it might not develop at all.
fc = The fraction of planets on which technology is developed
The fraction of planets with intelligent life that develop technological civilizations, i.e., technology that releases detectable signs of their existence into space.
L = The "Lifetime" of communicating civilizations
The length of time such civilizations release detectable signals into space.
You can work with this formula using the Drake Equation Calculator
This page was last updated on: 1/7/2011
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