The famous science fiction writer Arthur C. Clarke was quoted as saying, “Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.” A truer statement is hard to come by. Yet quote also sparks tremendous debate and intrigue among those whose ears come across it for the first time. We all wonder, are we reallyalone? Could we possibly be all that is out there? Is there truly no one looking back, wondering the same? Such questions have teased all of mankind, from our smartest scientists to the youngest of children and their endless curiosity. It is part of what makes us human, that we search for more than we just perceive around us. But perhaps there is a slightly more answerable question, can we quantify the possibility of life?
The answer is yes (and no). No we cannot provide hard numbers to a computer and have it spit out an answer which determines if there is life elsewhere in the universe, but yes we can get reasonable estimates. That is where the Drake Equation enters play. Postulated by Frank Drake back in 1961, the equation is an attempt to quantify, to our best estimates, the possibility of an intelligent civilization somewhere in our Milky Way Galaxy. By multiplying the estimated percentages of factors which we believe contribute to the possibility of intelligent life, and then multiplying that fraction by the total number of stars in the galaxy, out comes a simple number which guesses at the number of intelligent alien civilizations which we could theoretically make contact with. The factors of the Drake Equation include: the average rate of star formation in the galaxy, the fraction of those stars that have planets, the average number of planets per star that could potentially support life, the fraction of those planets that actually support life, the fraction of life-bearing planets with an intelligent species, the fraction of intelligent species that could develop technology to communicate across the cosmos, and finally, the length of time the average civilization lives. The first three fractions are the only ones which we actually have very accurate predictions. They are quantifiable and testable by astronomers. However, the last 4 are essentially just guesses. We may have some reason to set our guess one way or another but at the end of the day, one guess is no better than another. Depending on how one sets these factors, one could get the number of such civilizations to be 1e-10 or 1e4 and anything in between.
We can only speculate on the existence of alien civilizations. The Drake Equation is just a tool to help us along in the process. Nevertheless, considering the vastness of space and the lifetime of humans as individuals and possibly as a species, the chances that we ever make contact with another civilization may be extremely slim, regardless of how abundant life is in our universe. But until the day where either we become intelligent enough to travel these great distances or an alien comes knocking on our door, we may truly never know an answer to humanity’s greatest question… are we alone?
jblubin 