The Odds of Human Civilization Being Alone in the Galaxy: 1 in 60 Billion

The scientific likelihood of Humanity being the only technologically advanced species in the universe continues to become more and more remote, as recently illustrated by a tweaking of the Drake Equation by two researchers that posit that the odds of us being alone are 1 in 60 billion.

The purpose of the Drake Equation, as formulated by astronomer and astrophysicist Frank Drake in 1961, was to illustrate the possible number of civilizations that might exist that we could communicate with. While this was an interesting concept for the scientists attending the inaugural SETI meeting where the equation was first presented, it only concerns the possible number of civilizations that currently exist (or at least have existed within the recent past), and doesn’t take into account the rest of the nearly 14 billion years that the universe has been around, leaving plenty of time for even more civilizations to have formed and declined many times over.

Enter Adam Frank, from the University of Rochester’s Department of Physics and Astronomy, and Woody Sullivan, with the Department of Astronomy and Astrobiology Program at the University of Washington. Frank and Sullivan reframed the Drake Equation in their paper, "A New Empirical Constraint on the Prevalence of Technological Species in the Universe" to include the entirety of the existence of the universe, and instead of asking how many civilizations are out there, they ask "whether we are the only technological species that has ever arisen."

Working under the assumption that 20 percent of all stars have habitable planets orbiting them, Frank and Sullivan concluded that the chances of humanity being the only civilization in the universe were one in 1 heptillion. That’s 1 with 24 zeros after it. Or a million million million million, or a trillion trillion. To say that this is an astronomical number would be an gross understatement, but and Frank And Sullivan also point out that this 1 in one heptillion number is their lowest estimate — the probability of another civilization having formed is probably much, much higher.

When they narrowed the equation down to just include the stars in the Milky Way, the odds dropped significantly, but the odds of us being alone in our own galaxy still came in at 1 in 60 billion. And if the number of stars assumed to have hosted an advanced civilization were dropped to a much more conservative 1 in every million stars, the Milky Way would still be (or at lest have been) home to at least 300,000 civilizations.