1. This is the Drake Equation.
  2. Sometimes pop-sci articles say it answers the question "is there intelligent life in the universe?"
  3. But that's not a very good characterization.
  4. It might be more correct to say the Drake equation helps us ask the question more precisely.
  5. After all, the only answer we have to the question "Is there intelligent life in the universe?" is: ¯\_(ツ)_/¯
  6. Drake helps us reframe the question. It says "to answer that question here's everything we need to know."
  7. Then we can judge how much we do and don't know, and work towards a better and better answer.
  8. The equation is essentially just a bunch of terms multiplied together:
  9. R★ — The rate of star formation in the universe.
    How fast does the universe make new stars? We have a pretty good sense of this. Our galaxy produces about seven per year on average, and we have a good estimate of the number and size of galaxies in the visible universe.
  10. f(p) — Fraction of stars orbited by planets.
    This is one of the most exciting factors because when I was young we really had no idea. But thanks to awesome ongoing science including the amazing Kepler mission we now know this factor may be close to 1: it is starting to seem like pretty much all stars have planets.
  11. n(e) — Average number of earth-like bodies found in a planet-bearing star system.
    Again, until very recently we had no idea. But Kepler data has taught us a ton about the prevalence of planets similar to ours in size and proximity to their host stars. Considering just size and position, A good estimate right now is about 0.4. We don't know much about the atmospheres of exoplanets yet but missions now in development will help close that gap.
  12. f(l) — Fraction of planets suitable for life that actually go on to develop life.
    We only have ourselves to look at here so we don't know anything with certainty. On earth, life popped up very soon after the planet became suitable to it, and life has adapted to very diverse conditions. But as far as we know it only started once. And earth may be weird. We continue to search for evidence of past life on Mars, and we're doing exciting pre-planning for searches on other bodies. If we can find and study even extinct microbial life it will allow us to begin making estimates here.
  13. f(i) — Fraction of life that develops intelligence.
    Again, we only have ourselves to go on, which isn't much. There's no good consensus for this value and we're nowhere near solving that. But we can keep trying!
  14. f(c) — Fraction of intelligent life that produces detectable signals.
    Earth has had intelligent life for 200,000 years and we've only been sending signals into space for less than a hundred years. Is that normal? Fast? Slow? We don't know.
  15. L — Average lifetime of an intelligent civilization.
    How long will we continue to thrive, grow, learn, and push further into the universe? The universe is very very old and we are very very young. It is possible intelligent life is "common" but so short-lived that two civilizations never coexist.
  16. If we knew the precise value for every term we could plug them in and get a valid probabilistic estimate of the number of intelligent civilizations out there that we could hope to detect.
  17. The coolest thing about the Drake equation is how beautifully it illustrates why our growing knowledge of esoteric subjects is interesting.
  18. There's a penchant for anti-intellectualism these days so you often hear people dismiss scientific inquiry on the grounds that what is being studied is small and unimportant.
  19. The Drake equation reminds us that big questions — who we are, how we came to be, where we're going — are really just incredibly complex intricate collections of small questions that might otherwise seem pointless.
  20. And it reminds us that our ever-increasing knowledge is a beautiful and uniquely human thing.
  21. And finally it gives us hope that by continuing to ask and answer and improve our understanding we may be stretching our own L.
  22. And I think our L is worth stretching.