Common sense tells us that the idea of being alone in the universe is infinitesimally small. There are thousands of solar systems in the Milky Way alone, and in the visible universe there are trillions of galaxies. And that is just the observable Universe. The real universe is quadrillions of times bigger, because it is constantly expanding. Therefore, it is statistically improbable that we are alone. A human’s chances of being born are one in 400 trillion, but if life on earth is the only form of life in the Universe, that chance becomes unbelievably small.
The size of the Universe is not the only variable that determines whether there is life out there. How many other planets could support life? If there is other life somewhere out there, is it intelligent? Is it near enough to us that we could ever make contact? In 1961 American astrophysicist Frank D. Drake devised a simple equation that could determine whether extraterrestrial intelligence is possible.
The equation is made up of seven variables, each of which represents an unknown quantity. When combined, they produce an estimate of the number of civilizations we might be able to make contact with in our galaxy. Here’s a breakdown of all the factors:
In the Milky Way, stars form at a rate of R*. Some (fp) of those stars have planets, but a smaller percentage (ne) of those planets are capable of supporting life, and an even smaller percentage (f1) of those actually develop at least basic life. A fraction (fi) of those planets with any life may develop intelligent life. And of those intelligent life forms, an even smaller fraction (fc) will have the technology to communicate with us.
The final factor in the Drake equation accounts for how long (L) these intelligent, technologically advanced civilizations will exist before they self-destruct or otherwise disappear.
