It’s been over half a century since Frank Drake developed an equation to estimate the probability of finding intelligent life in our galaxy. We’ve learned a lot since then, prompting an astrophysicist from MIT to come up with her own take on the equation. Here’s how the new formula works — and how it could help in the search for alien life.
The new formula was devised by Sara Seager, a professor of planetary science and physics at the Massachusetts Institute of Technology. I contacted her to learn more about the new equation and why the time was right for a rethink.
Assessing the Probability of Intelligent Life
Back in 1961, Frank Drake proposed a probabilistic formula to help estimate the number of active, radio-capable extraterrestrial civilizations in the Milky Way Galaxy. It goes like this:
- N is the number of civilizations in our galaxy with which we might hope to be able to communicate
- R* is the average rate of star formation in our galaxy
- fp is the fraction of those stars that have planets
- ne is the average number of planets that can potentially support life per star that has planets
- fl is the fraction of the above that actually go on to develop life at some point
- fi is the fraction of the above that actually go on to develop intelligent life
- fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
- L is the length of time such civilizations release detectable signals into space
People have plugged in a variety of values over the past 50 years — all of them purely speculative. Values for N have ranged anywhere from one (i.e. here's looking at you kid) up to the millions.
“The original Drake Equation just gave us the format with which to see what the different ingredients would be,” Seager told io9. “No one had ever quantitatively organized our thoughts before. That’s the revolutionary nature of the equation.”
But it can never give us a quantitative answer, she says, and we shouldn’t expect the equation to be a real equation in the sense that we can have precise definitions for each term.
“It’s a wonderful, amazing, innovative way for us to think about intelligent life — or the existence of intelligent life,” she says, “But there are just so many unknowns that can’t be quantified.”
But things have changed since 1951. Thanks to the Kepler Space Telescope, we now know that there's an absolute plethora of exoplanets out there. What’s more, they come in all sorts of shapes and sizes, they orbit a diverse array of stars, and they reside in solar systems that scarcely resemble our own. Our sense of the galaxy is changing dramatically with each new discovery — as is our sense of its potential to harbor life.