Like HowStuffWorks on Facebook!

A Simple Equation Calculates the Likelihood of Alien Intelligence, But...

Popular rappers aside, Drake has been a household name since the 1960s. Well, in scientific households, at least. And while "Hotline Bling" may get more recognition these days, a bit of mathematical language called the Drake Equation is still going strong, a testament to our desire to quantify the unknowable universe.

As BrainStuff host Josh Clark explains in the above video, the Drake Equation is a formula used to estimate the odds of finding intelligent life in the universe, and it was preceded by an evocative question: "Where are they?"

The query was posed by physicist Enrico Fermi in 1950 during a lunch break at work — just another average day making nuclear bombs at the Los Alamos National Laboratory. Fermi asked his dining companions to consider the odds that other civilizations existed, and whether these civilizations could communicate with people on Earth. Considering the age of the universe and the number of planets that could possibly sustain life, shouldn't the universe be teeming with life? And, shouldn't many of these life-forms be intelligent, with at least some life-forms discovering how to travel the universe? Yet there isn't definitive evidence that we aren't alone in the world — an observation that became known as the Fermi Paradox.

In the years after Fermi posed the question, many scholars and laypeople alike attempted to answer it. One of the most well-known attempts is known as the Drake Equation. In 1961, an astronomer named Frank Drake organized the first conference of the Search for Extraterrestrial Intelligence (SETI) Institute. At the inaugural convening of SETI, Drake debuted his now-famous, and surprisingly simple, equation that requires at least some speculative input. Why so much guessing? There's still a lot we don't know about our universe.

SETI founder Frank Drake photographed at his California home in 2015.
SETI founder Frank Drake photographed at his California home in 2015.
Ramin Rahimian/The Washington Post/Getty Images

The Drake Equation goes like this: N=R* x fp x ne x f1 x fi x fc x L

The letter "N" equals the number of intelligent civilizations who Earthlings could possibly communicate with in the Milky Way, and is what the equation is designed to answer.

R* is the rate of star formation, which astrophysicists have determined is equal to about three solar masses each year. Although a solar mass is equal to our sun, the three solar masses in question could form any combination star sizes, from gargantuan to minute. Using our sun as a measurement is a way of quantifying the formation.

Next, fp stands for the fraction of those stars that have planets orbiting them, and ne stands for the number of those planets capable of supporting life because they orbit the star within the Goldilocks Zone (not too hot, not too cold, but just right). These exoplanets number about 3,400 within the Milky Way.

Thus far, we can be pretty confident of the numbers plugged into the Drake Equation, but it gets more difficult as things enter the territory of information we just don't have (yet). That's because f1 stands for the fraction of exoplanets where life has evolved, and fi stands for exoplanets that have developed intelligence. Then, fc represents the fraction of intelligent life that has developed communication and transmitted it in ways we can detect along the electromagnetic spectrum. Lastly, L stands for the longevity of this communication. In other words, how long does an intelligent civilization transmit in a way we can detect before they go extinct or find a new means of communicating we can't detect?

At this point, you may be wondering about the usefulness of the Drake Equation. The truth is, it's an elegant way to tackle the question of life in the universe. The problem is, we don't know enough about the universe to plug in the correct factors — or even to make an educated guess about four of the seven variables.

Some scientists have argued against life existing elsewhere. But that desire to know for sure is just one of the reasons astrobiologists, astrophysicists and astronomers are still searching the universe, parsing data and hoping that one day we may eventually fill in the blanks in the Drake Equation. 

More to Explore