The equation is made up of seven variables that, when multiplied together, yield a calculation of the possibility that humanity might someday hear from an intelligent alien civilisation (one that has achieved the ability to transmit radio signals that we can detect on Earth).
The problem is that we don’t know the value of many of the Drake equation variables with any degree of certainty. Scientists have a good handle on the first three: the rate of star formation, the number of those stars with planets, and the number of those planets within the stars’ Goldilocks zone. But the rest are still a mystery.
This post has been updated with new information. It was originally published on October 9, 2019.