The Drake Equation, developed by astronomer Frank Drake, is an equation that estimates how many alien civilisations might live in our galaxy. But the more we find out about the way of the milky, the less chance alien life exists. Just check out the difference between how much alien life existed before when the Drake Equation was invented and how much alien life is estimated to exist now.
The interactive featurette is over at BBC Future and it's fun to tweak it to see the possibility of alien civilisations theoretically communicating right now.
Try it out yourself, the equation obviously isn't the be all, end all proof of alien life, it's, according to the BBC, "more a tool used to help understand how many worlds might be out there and how those estimates change as missions like Kepler, a telescope that is currently searching for Earth-like planets, begin to discover more about our universe." But then again, all it takes is one discovery to blow this equation up. [BBC]