07-08-2003, 08:37 AM
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#16 (permalink)
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Squid
Location: USS George Washington
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Here's the formula...
Quote:
Calculation of Intelligent Civilizations
The very first meeting in modern times to discuss the possibility of extraterrestrial intelligence was held by the National Academy of Sciences in November 1961 at Green Bank, West Virginia... Eleven prominent scientists met... to discuss extraterrestrial intelligent life and interstellar communication....
The product of the meeting was a formula to determine the possibility of extraterrestrial intelligence. Each variable in the equation is subject to different qualifications, however, and five years after the meeting Dr. Carl Sagan came to a different conclusion from that of this meeting. The two results are compared below:
N=R*fpnefefifcL
N is the number of extant civilizations possessing interest and the capability for interstellar communication.
R* is the mean rate of star formation averaged over the lifetime of the galaxy. The Green Bank (GB) group said this was the total number of stars in the galaxy divided by the lifetime of the galaxy. By their values this was
1010/1010 or 1
Sagan used 1011 as the total number of stars, so his value for R is
1011/1010 or 10
fp is the fraction of stars with planetary systems. GB said the value for this would be either 0.4 or 0.5; Sagan said 1.
ne is the mean number of planets in each planetary system with an environment favorable for the origin of life. Feeling that our sun was unexceptional in this regard for a star of its class, GB said between 1 and 5; Sagan uses 1.
fl is the fraction of suitable planets on which life does develop. Agreeing that life on such planets would be inevitable, both use the value of unity, 1.
fi is the fraction of life-bearing planets on which intelligence accompanied with manipulative ability appears. Here the issue of dolphins arises, for although they are considered by many to be intelligent beings, they have no manipulative ability, and therefore do not fit this equation. Using the same arguments to deduce their answers, GB and Sagan come to different conclusions: the former uses 1 and the latter 10-1.
fc is the fraction of planets on which an advanced technical civilization evolves. Both GB and Sagan adopt a 10-1 value for fc.
L is the lifetime of the technical civilization and the most difficult variable to determine. (The L period of Earth just recently began with the development of the radio telescope, since only then did we become capable of communicating with other civilizations in space).
At Green Bank they considered the two extremes of a civilization destroying itself in less than 1,000 years, or overcoming its crises and lasting almost indefinitely, or more than 100 million years.
For the Green Bank group, then, the lower limit for N would be:
1 X .4 X 1 X 1 X 1 X .1 X 1000 = 40
The upper limit would be
1 X .5 X 5 X 1 X 1 X 1 X .2 X 100,000,000 = 50,000,000.
Sagan chooses the extremes of L less than 100 or greater than 108, assuming an average of 107. His lower limit for N is therefore:
10 X 1 X 1 X 1 X 10-1 X 102 = 10
His upper limit is:
10 X 1 X 1 X 1 X 10-1 X 10 -1 X 107 = 106
Excerpted from Possibility of Intelligent Life Elsewhere in the Universe, Report prepared for the Committee on Science and Technology U.S. House of Representatives, DOC Y 4.SCI 2:94-1-r, 1975. Pages 6-7.
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Crap, the subscripts in the formula didn't work too well. Here's the link...
http://www.techtv.com/screensavers/p...321430,00.html
-Mikey
Last edited by MikeyChalupa; 07-08-2003 at 08:40 AM..
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