Contacting extraterrestrials

Our sun is only a single star in a collection of over 400 billion we call the Milky Way galaxy. The Milky Way is only 1 of billions of galaxies in the universe. The astronomer Frank Drake was the first who attempted to estimate how much life is in the universe. He came up with a simple equation, now called the Drake Equation, that maps out the possibilities: N = R x f_p x n_e x f_l x f_i x f_c x L. "N" here represents the number of communicating civilizations in our Milky Way galaxy. This number depends on several factors. "R" is the rate of "suitable" star formation in the galaxy. "f_p" is the fraction of stars that have planets. "n_e" is the number of these planets around any star within the suitable ecosphere of the star. An "ecosphere" is a shell that surrounds a star within which the conditions are suitable for life to form. Too close and it's too hot; too far and it's too cold. "f_l" is the fraction of those planets within the ecosphere on which life actually evolves. "f_i" is the fraction of those planets on which intelligent life evolves. "f_c" is the fraction of those planets where intelligent life develops a technology and attempts communication. The last factor, "L," is the length of time that an intelligent, communicating civilization lasts.

One result of the Drake Equation gives N = L. In other words, the number of intelligent communicating civilizations in the galaxy equals the number of years such a civilization lasts. The figure about which we know the least bears a great significance in our calculations. Most scientists hope that if a civilization can overcome its initial tendency to destroy itself with its own technology, then that civilization is likely to last for a very long time. Let's hope those scientists are right. In any case, there should be at least 50 (the number of years we've been around communicating) and if a communicative civilization lasts for millions of years, there may possibly be millions of civilizations we can look for.