The Drake Equation: The coolest equation you’ll ever understand?

Science is full of equations, some relatively simple, lots of them not so simple. I suspect most of coolest equations require a PhD in quantum physics to understand. The Drake Equation is not one of these though. It’s only a freakin’ equation for predicting the number of intelligent alien civilizations in our Galaxy! Put that in your pipe and smoke it Dr Quantum Physics PhD.

It’s named after its inventor, Frank Drake. Back in 1961 Drake was asked by the US National Academy of Sciences to hold a meeting about finding intelligent aliens. In preparation Drake wrote an agenda and included all the things you’d need to know in order to find alien life. He quickly realized they could be combined into the following equation:

The number of intelligent alien civilizations in our galaxy is =

  1. the rate at which stars form in our galaxy
  2. x the % of stars with planets
  3. x the % of these planets in a habitable zone
  4. x the likelihood of life emerging
  5. x the likelihood of intelligent life evolving
  6. x the number of intelligent civilizations that emit signs of their existence (like radio waves)
  7. x the average length of time intelligent civilizations survive

Simple huh? Just seven variables. All you need to do is put in numbers and then multiply them together and out pops your answer. At this point lots of tiresome people begin criticizing the equation, because we don’t actually know what most of the values for each variable actually are. They get all whiney and say thing like “its not a real equation”. But this is totally missing the point, the Drake Equation is important because it orders our thinking, it shows us exactly what we need to know and even puts it in an order for us. In fact, this one equation pretty much forms the backbone of astrobiology as a science.

Even though we don’t know the actual values its still fun putting in your own estimates and seeing which number pops out the other end. Frank Drake got 10, the version on Wikipedia gets 2.31, I can get a range between 1 and millions. Carl Sagan believed the Drake Equation showed the chances of intelligent alien life were high and was thusly inspired.

So what do we know? Scientists are reasonably certain about the rate of star formation in our galaxy (around 7 per year). Since 1992 astronomers have been finding more and more exoplanets and as of today 506 exoplanets are confirmed. The number of Sun-like stars with planets is believed to be around 40% or higher. Currently most of the planets found are massive and orbit very close to their stars (they’re called Hot Jupiters), but as detection techniques improve scientists think many more planets will be found of different sizes and orbits (more on this is a later post).

As for the rest, it’s all up in the air, as we are our only example. We only know of one habitable planet, which has produced intelligent life once. So far we have no idea if this has happened elsewhere. We also have no idea how long humans will be around. Most of us tend to assume we’ll be around forever; our technology will save us from any disaster. I suspect most palaeontologists quietly smirk at this; they know all species go extinct eventually.

Hopefully as science progresses we’ll become more and more certain about the values in Drakes Equation, we’ll discover a more representative sample of exoplanets, learn more about how life started, and learn more about the chances of evolution producing intelligence. Or we’ll learn that an omnipotent God with a white beard created us as his special race and that we’re totally going to heaven when we die… jokes.

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1 Response to “The Drake Equation: The coolest equation you’ll ever understand?”



  1. 1 The Fermi Paradox: A lonely galaxy? « Astrobioloblog Trackback on January 6, 2011 at 9:57 pm

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