by Joe Pitkin

Science fiction writers love aliens. We believe in their existence; we dream of hearing from them. As a boy, I remember seeing Carl Sagan’s explanation of the Drake Equation—a string of variables that estimates the number of extraterrestrial civilizations in the galaxy—and being struck both by the possibilities of interstellar neighbors and by the tremendous uncertainty in the variables.

Those of you who have spent time meditating on the Drake Equation know that its variables f_p and n_e, representing the number of planets in the galaxy and the fraction of those planets harboring environments suitable for life, have been pinned down with greater and greater confidence in the last two decades. You know, too, that the value of these variables is very, very high. But many of the other variables in the Drake Equation remain highly uncertain, even suspect in a couple of…