The only intelligent life forms we know of reside here on Earth. But that hasn’t stopped us from trying to answer the question: “Are we alone?”
Richard Lawn | NAUTILUS
The search for extraterrestrial intelligence now has an accepted acronym, SETI, and a growing number of interested participants. The odds of galactic company can only be estimated, and a primary tool to predict the number of other civilizations out there is the Drake Equation. Nearly everyone interested in SETI has heard of it. But views of its utility vary widely. To some, it is a useful way to estimate the number of technological civilizations in our galaxy and the chances of detecting an extraterrestrial message. Others view it as a wasted effort, given the huge range of conjectures involved in its components. There is a middle ground to use it to update and assess the reliability of relevant data that we have and the ways to improve upon the uncertainties. It can certainly be an effective tool for stimulating curiosity on this subject.
Frank Drake presented the equation in 1961 at what may have been the first formal SETI conference at the National Radio Astronomy Observatory in West Virginia. The intent was likely to stimulate discussion and evaluate proposed research, not to arrive at a true estimate of the number of intelligent ETs whose signals we could detect by multiplying its components. In its original form, the Drake Equation is:
N = R* x fp x ne x fl x fi x fc x L where:
· N is the number of intelligent civilizations in the Milky Way Galaxy, who, for this exercise, emit radio, light, or other transmissions that are detectable from afar.
· R* is the rate of star formation per year for the galaxy.
· fp is the fraction of those stars with planets.
· ne is the average number of planets capable of supporting life (think of e for “earth-like” or “ecologically fit”).
· fl is the number of those that actually develop life.
· fi the number of those where life becomes intelligent.
· fc the fraction of those emitting detectable signals into space
· L the lifetime of a communicating civilization.
Multiplying the terms would yield estimates that range from a galaxy teeming with ETIs (extraterrestrial intelligent beings) to us alone. Though ET has yet to phone in, advances in astronomy since 1961 have firmed up the estimates of some of these terms. Let’s revisit each of them.
N is usually considered the number of communicating civilizations in just our Milky Way galaxy. But keep in mind that there are hundreds of billions of other galaxies and their stars much farther away in the visible universe.
The factor R* is estimated ~1 by some astronomers, based on the current rate of star formation in our entire galaxy. But the rate of star formation was once higher, and dividing the number of stars in the galaxy (200-400 billion) by its estimated age (roughly 10 billion years) would yield an R* closer to 10 per year, the number I will choose to plug in.