The Drake equation quantifies the probabilistic argument that gives the approximate number of active extraterrestrial civilizations in our galaxy or the whole Universe. At its original form Drake equation has 7 factors, including the average star formation rate, the fraction of stars that have planets, the number of planets per star and others. Even though the equation seems extremely simple at the first glance, coming up with sensible values for the factors is much harder than one might think.
In this recent TEDx video Fred Crawford, who has been teaching physics for over 30 years, discusses the main factors of Drake’s equation and describes how we arrive to sensible values of each of them. For more similar videos use the links below.