Drake Equation is an equation used to estimate the potential number of extraterrestrial civilizations in the Milky Way galaxy. It is used in the fields of exobiology and the search for extraterrestrial intelligence (SETI). The equation was devised by Frank Drake in 1962.
Where :
N = the number of civilizations in our galaxy with which communication might be possible ;
and
R* = the average rate of star formation per year 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 the above that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life
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
Considerable disagreement on the values of these parameters exist, there are several disagreement on the value of the parameters, thus resulting in different answers :
Drake | Current | Pessimist | Optimist | |
N | 10 | 2.31 | 0.000065 | 20000 |
R* | 10 | 7 | 10 | 20 |
fp | 0.5 | 0.5 | 0.5 | 0.5 |
ne | 2 | 2 | 0.01 | 2 |
fℓ | 1 | 0.33 | 0.13 | 1 |
fi | 0.01 | 0.01 | 0.001 | 0.1 |
fc | 0.01 | 0.01 | 0.01 | 0.1 |
L | 10000 | 10000 | 1000 | 100000 |
Current estimate is based on NASA and the European Space Agency (2008) R* = 7 ; and fℓ = 0.33 ,
\ Current N = 2.31 ( 2 communicative civilization exist in our galaxy at any given time, on average, plus 200 more that are not trying to communicate )
A pessimist believes that suitable planets are rare, life seldom becomes intelligent, and intelligent civilizations do not last very long, thus a Pessimist N = 0.000065. ( we are almost surely alone in our galaxy )
Alternatively, making some more optimistic assumptions, assuming that planets are common, life always arises when planets are favorable, 10% of civilization become willing and able to communicate, and then spread through their local star systems for 100,000 years : an Optimistic N = 20,000 ( there’s quite a few civilizations, although the closest one would still be about 1,500 light years away. )
Criticism
1. The equation is largely based on conjecture, thus cannot be used to draw firm conclusions of any kind.
2. Drake Equation assumes that civilizations arise and then die out within their original solar systems. If interstellar colonization is possible, then this assumption in invalid, and the equations of population dynamics would apply instead.
3. Drake originally formulated the equation merely as an agenda for discussion at the Green Bank Conference. Even though the Drake Equation involves speculation about unmeasured parameters, it was not meant to be science, but intended as a way to stimulate dialog on these topics.
4. Drake Equation is a Fermi problem which involves the multiplication of several estimated factors. The basic question of why, if there is a significant numbers of such civilizations, ours has never encountered any others is called the Fermi paradox.
