The Drake equation is advocated by SETI (Search for Extra Terrestrial Intelligence) to show that the probability for ETI has a high probability (N).
- N* Number of stars in the Milky Way
- fp Number of habitable planets in each system
- ne number of planets that are Earth like
- fl number of planets that emerge from inorganic matter or organic precursors
- fi fraction of those planets on which intelligent beings also evolve
- fc fraction of those planets on which sufficient communications technology arises
- fL fraction of average planet lifetime
The problem with the equation is that each f is a number between 0 and 1, the product of the equation will be vastly lower than the total number of suitable stars in the galaxy N*. Many variables are unknown. So, the numbers that are brought in depend profoundly on the assumptions we bring into the problem.