We've discussed just about every aspect which ultimately determines the likelihood of Communicating with intelligent life in the universe. It's time to make a quantitative estimate of the numbers.
First proposed by astronomer, Frank Drake, in the early 1960s, the Drake equation allows us to make a quantitative estimate of the number of civilizations in the galaxy with which we might communicate. It does not tell us how many planets have life (this is a much larger number, to be sure!) or even the number of intelligent civilizations (again, a larger number).
| Rs | The star formation rate in the galaxy (stars/year) |
| fp | The fraction of stars with planets (0.0 to 1.0) |
| n | The number of habitable planets in a typical solar system (0,1,2, etc) |
| fl | The fraction of habitable planets which develop life (0.0 to 1.0) |
| fi | The fraction of planets with life which develop intelligence (0.0 to 1.0) |
| fc | The fraction of intelligent species willing to communicate (0.0 to 1.0) |
| L | The average lifetime of a communicating civilization (years) |
Rs, the star formation rate in the galaxy, astronomers can give us a fairly well constrained value
of about 10 stars/year.
fp, the fraction of stars with planets (0.0 to 1.0), is certainly greater than 0.05 (current
fraction detected so far). A conservative guess would be 0.2.
Try the Drake Equation yourself! (this version uses a slightly different multiplier at the top (Nx verses Rs)
Fermi's Paradox: If intelligent life existed anywhere in the Galaxy, they'd know about us. Even traveling at 1/100th the speed of light, it would take just 10 million years for a civilization to cover the entire galaxy (only a fraction of the universe age).