For many of us it will take quite a drive in order to escape the light pollution of urban metropolises… but the reward of being able to see the array of countless stars in the night sky is certainly worth the effort. Through experiences such as these we may find ourselves asking, where are all the aliens?
First proposed by Frank Drake in 1961, the Drake equation is used to derive an estimate of the number of active extraterrestrial civilisations in the Milky Way galaxy to which communication may be possible. The equation is formed from the product of a series of numerical estimates and fractional values:
We consider the rate of formation of stars suitable for the development of intelligent life R*; we consider the fraction of those stars which have planetary systems, fp; we consider the average number of planets per planetary system which have an environment suitable for life, ne; we consider the fraction of those planets on which life actually develops, fl; we consider the fraction of those planets on which intelligent life develops fi; we consider the fraction of civilisations which are able to develop a technology that releases detectable signals of their existence into space, fc; and finally we consider the length of time that such civilisations have been releasing these detectable signals into space, L. Our final product is N, the number of civilisations in the Milky Way galaxy who have released detectable signals into space. It’s quite thorough, I agree.
The Drake equation is sadly an estimate, and a very speculative estimate at that. How does one estimate the fraction of planets on which intelligent life develop for instance, when our current sample consists of only the Solar System? Consequently the Drake equation yields a wide range of results. Extremely low estimates are on the order of 10-10, suggesting that we are likely to be alone in the Milky Way or even in the entire observable universe. On the other hand, high estimates are on the order of millions, which raises the question of why we have not yet encountered extraterrestrial life.
The Drake equation is one of many factors involved when considering the Fermi paradox, an argument made by physicists Enrico Fermi and Michael H. Hart in the early 20th century. It describes the apparent contradiction between the high estimates of the number of intelligent, extraterrestrial civilisations and the lack of evidence for such civilisations.
For the time being enjoy this twist on the Drake equation.