How many intelligent civilizations should there be in our galaxy right now? In 1961, the US astrophysicist Frank Drake, who passed away on Sept. 2 at the age of 92, came up with an equation to estimate this (opens in new tab). The Drake equation, dating from a stage in his career when he was “too naive to be nervous” (as he later put it), has become famous and bears his name.
This places Drake in the company of towering physicists with equations named after them including James Clerk Maxwell and Erwin Schrödinger. Unlike those, Drake’s equation does not encapsulate a law of nature. Instead it combines some poorly known probabilities into an informed estimate.
Whatever reasonable values you feed into the equation (see image below), it is hard to avoid the conclusion that we shouldn’t be alone in the galaxy. Drake remained a proponent and a supporter of the search for extraterrestrial life throughout his days, but has his equation really taught us anything?
Related: The search for alien life
Drake’s equation may look complicated, but its principles are really rather simple. It states that, in a galaxy as old as ours, the number of civilizations that are detectable by virtue of them broadcasting their presence must equate to the rate at which they arise, multiplied by their average lifetime.
Putting a value on the rate at which civilizations occur might seem to be guesswork, but Drake realized that it can be broken down into more tractable components.
He stated that the total rate is equal to the rate at which suitable stars are formed, multiplied by the fraction of those stars that have planets. This is then multiplied by the number of planets that are capable of bearing life per system, times the fraction of those planets where life gets started, multiplied by the fraction of those where life becomes intelligent, times the fraction of those that broadcast their presence.
When Drake first formulated his equation, the only term that was known with any confidence was the rate of star formation — about 30 per year.
As for the…