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| Frank Drake at board |
The Drake equation is a an argument often used by scientists, journalists, and UFO investigators to estimate the number of active extraterrestrial civilizations in our Milky Way galaxy.
The equation was written in 1961 by Frank Drake, as a
way to stimulate scientific dialogue at the first scientific meeting on
the search for extraterrestrial intelligence (SETI).
The equation summarizes the main concepts which scientists must
contemplate when considering the question of other radio-communicative
life. It is thought of as an estimation rather than as a precise number.
"As I planned the meeting, I realized a few days ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it's going to be to detect extraterrestrial life. And looking at them it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy. This was aimed at the radio search, and not to search for primordial or primitive life forms."
- —Frank Drake
The Drake equation is:
Where:
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.
Using this equation, how many intelligent civilizations could there be in our the Milky Way Galaxy?
Original estimates
The educated guesses used by Drake and his colleagues in 1961 were:
- R∗ = 1 yr−1 (1 star formed per year, on the average over the life of the galaxy; this was regarded as conservative)
- fp = 0.2 to 0.5 (one fifth to one half of all stars formed will have planets)
- ne = 1 to 5 (stars with planets will have between 1 and 5 planets capable of developing life)
- fl = 1 (100% of these planets will develop life)
- fi = 1 (100% of which will develop intelligent life)
- fc = 0.1 to 0.2 (10–20% of which will be able to communicate)
- L = 1000 to 100,000,000 years (which will last somewhere between 1000 and 100,000,000 years)
Inserting the above numbers into the equation gives a minimum N of 20. Inserting the maximum numbers gives a maximum of 50,000,000. Drake states that given the uncertainties, the original meeting concluded that N ≈ L, and there were probably between 1000 and 100,000,000 planets with civilizations in the Milky Way galaxy.
Whether or not this is accurate remains, of course, to be seen. Even with our advancements in science it could be hundreds of years or more before we get an answer to this question. Of course, millions of humans on planet Earth will attest to the fact that there are alien civilizations visiting us right now, and have been for eons. As for the species visiting our planet now they are much further advanced than humans, so our contact with them is fleeting at best in most instances, leaving the witness or experiencer with more questions than answers. For those of us who have had contact with extraterrestrials, there is no further proof needed that there are indeed other life forms in our Milky Way Galaxy.
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Margie Kay is an investigator and author living in Kansas City, Missouri. Visit www.margiekay.com for more information.
