The Drake Equation
The world is likely to find alien life. It could happen even sooner, depending how many civilizations are out there to be found. To understand why this is, it helps to know about someone name Frank Drake.
Drake is the least lonely man on Earth—if not in the entire galaxy. Most of us are reserving judgment on whether there is intelligent life on other planets; we haven’t even found bacteria yet, much less a race of aliens with Internet service and takeout food. But Drake, an astrophysicist and chairman emeritus of the California-based SETI (Search for Extraterrestrial Intelligence) Institute, has no such doubts.
It was in 1961, when he was working at the National Radio Astronomy Observatory in Green Bank, W. Va., that Drake developed the eponymous—and now famous—Drake Equation, which calculates how many advanced and detectable civilizations there should be in the Milky Way in any one year. The number turns out to be potentially huge, and while it’s admittedly based on a number of Earth-centric suppositions—the collapse of any one of which calls much of the equation into question—all of those suppositions are based in increasingly solid science.
Start with the number of stars in our galaxy, which is conservatively estimated at 100 billion, though is often cited as three times that. Of those 100 billion, from 20% to 50% probably harbor planetary systems—an estimate that becomes more and more reliable as the Kepler Space Telescope and various ground-based observatories detect increasing numbers of exoplanets.
Not all of those exoplanets would be capable of sustaining Earth-like life, so the equation assumes from 1 to 5 in any system could. Of those bio-friendly worlds, from 0% to 100% would actually go on to develop life. And of those world, in turn, from 0% to 100% would develop life forms that we would consider intelligent.
The mere existence of intelligent life forms tells us nothing, however, unless they have the ability to make themselves known—which means to manipulate radio waves and other forms of electromagnetic signaling. Drake estimates that from 10% to 20% of the smart civilizations would clear that bar.
“Other intelligent life-forms will differ greatly in appearance – they may resemble the creature in E.T. or startle us with their beauty – but life itself is common, I’m certain.”~ Frank Drake
Finally, and perhaps most anthropocentrically, the equation considers how long any one of those semaphoring civilizations would be around to blink their signals our way. A sun like ours survives for about 10 billion years; life on Earth has been around for only about 3.5 billion years, and humans have been radio-capable for barely a century.
If we destroy ourselves in an environmental or nuclear holocaust tomorrow, our signal will go dark then. If we survive for tens of thousands of years, we will be announcing our presence to the cosmos for far longer—and the same is true of all of the other civilizations that live in the Milky Way.
Factor all of this together and stir in a little statistical seasoning concerning our increasing ability to study other star systems for signals, and, as the above interactive shows—the results can vary wildly. If you play the game conservatively—lowballing all of the variables—you might get about 1,000 detectable civilizations out there at any given time. Play it more liberally and you get hundreds of millions. The interactive let’s you play that game yourself. Imagine there are 10,000 detectable civilizations and we are likely to find alien life by 2040. If there are a million, we’d discover alien life by 2028.
Nobody pretends the Drake Equation is the final word. Even its enthusiasts admit that it is, at best, a way to “organize our ignorance.” But organized ignorance is a whole lot better than the disorganized kind; and it is, almost always, a starting point toward wisdom.
Astronomers looking for alien signals have examined only a few thousand star systems so far. But as SETI Institute senior astronomer Seth Shostak has noted, the rate at which researchers are able to process the massive amounts of data that radio telescopes receive doubles approximately every 18 months to two years, meaning it grows by a factor of ten every six years or so.
The Milky Way has around 100 billion (1011) star systems that could conceivably host intelligent life under our current assumptions. An estimate of 100,000 (105) active civilizations in the galaxy would mean one per million star systems. At the exponential rate of growth in signal processing, researchers will have examined one million candidates by around 2034, bringing the odds of a discovery into the probable. Adding or removing a zero from the estimate of the number of civilizations out there merely adds or subtracts six years from the estimate, respectively, since that’s how long it takes to expand our search proportionally. See you in 2040, aliens.