N = the number of civilizations in the Milky Way galaxy with which communication might be possible (i.e. which are on the current past light cone);
and R∗ = the average rate of star formation in our Galaxy.
fp = the fraction of those stars that have planets.
ne = the average number of planets that can potentially support life per star that has planets.
fl = the fraction of planets that could support life that actually develop life at some point.
fi = the fraction of planets with life that go on to develop intelligent life (civilizations).
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = the length of time for which such civilizations release detectable signals into space.
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 written 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.
In 1960, Frank Drake conducted the first search for radio signals from extraterrestrial civilizations at the National Radio Astronomy Observatory in Green Bank, West Virginia. Soon thereafter, the National Academy of Sciences asked Drake to convene a meeting on detecting extraterrestrial intelligence. The meeting was held at the Green Bank facility in 1961. The equation that bears Drake's name arose out of his preparations for the meeting.
This meeting established SETI as a scientific discipline. The meeting's dozen participants - astronomers, physicists, biologists, social scientists, and industry leaders - became known as the "Order of the Dolphin". The Green Bank meeting has been commemorated by a plaque at the site.
The Drake equation is closely related to the Fermi Paradox in that Drake suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations (the Fermi paradox) suggests that technological civilizations tend to disappear rather quickly. This theory often stimulates an interest in identifying and publicizing ways in which humanity could destroy itself, and then counters with hopes of avoiding such destruction and eventually becoming a space-faring species.
A similar argument is the Great Filter, which notes that since there are no observed extraterrestrial civilizations, despite the vast number of stars, then some step in the process must be acting as a filter to reduce the final value. According to this view, either it is very hard for intelligent life to arise, or the lifetime of such civilizations must be relatively short.
A final argument is the Zoo Hypothesis, which states that super-intelligent extraterrestrial life exists and does not contact life on Earth to allow for its natural evolution and development.
Carl Sagan, a great proponent of SETI, quoted the formula often and as a result the formula is sometimes mislabeled as "The Sagan Equation." Read more ...
Are We Alone In The Galaxy? Updated Drake Equation Suggests We Might Be Live Science - May 30, 2024
After the Fermi paradox came the Drake Equation, which attempts to quantify the number of intelligent civilizations in our galaxy, or the universe. In it, we can place knowns or best guesses as to the number of stars that contain (for instance) planets in habitable zones, or best guesses as to how many of those will be able to sustain intelligent life. sing these equations, scientists attempt to estimate the number of intelligent civilizations in the universe, and depending on their input, have come up with answers ranging from 30 to 100,000. Drake himself estimated a figure between 1000 and 100,000,000 in our galaxy alone.