And

"The Drake Equation"

The Drake equation is a probabilistic argument used to estimate the number of active,
communicative extraterrestrial civilizations in the Milky Way Galaxy. The equation
was formulated in 1961 by Frank Drake, not for purposes of quantifying the number of civilizations,
but 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 more properly
thought of as an approximation than as a serious attempt to determine a precise number.
Criticism related to the Drake equation focuses not on the equation itself, but on the
fact that the estimated values for several of its factors are highly conjectural, the combined
multiplicative effect being that the uncertainty associated with any derived value is so large
that the equation cannot be used to draw firm conclusions.

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The Drake equation amounts to a summary of the factors affecting the likelihood that we might detect
radio-communication from intelligent extraterrestrial life. The last three parameters, fi,
fc, and L, are not known and are very difficult to estimate, with values ranging over many orders of
magnitude (see criticism). Therefore, the usefulness of the Drake equation is not in the solving, but
rather in the contemplation of all the various concepts which scientists must incorporate when
considering the question of life elsewhere, and gives the question of life elsewhere a basis
for scientific analysis. The equation has helped draw attention to some particular scientific problems
related to life in the universe, for example abiogenesis, the development of multi-cellular life,
and the development of intelligence itself. 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. After about 50 years, the Drake equation is still of
seminal importance because it is a 'road map' of what we need to learn in order to solve this
fundamental existential question. It also formed the backbone of astrobiology as a science;
although speculation is entertained to give context, astrobiology concerns itself primarily with
hypotheses that fit firmly into existing scientific theories. Some 50 years of SETI have failed to
find anything, even though radio telescopes, receiver techniques, and computational abilities
have improved significantly since the early 1960s. It has, however, been discovered that our
galaxy is not teeming with very powerful alien transmitters continuously broadcasting near the
21 cm wavelength of the hydrogen frequency; this was not known in 1961.

(!!!!!TEXT BORROWED FROM WIKIPEDIA!!!!!)