We're actually not even clear on what conditions are necessary to generate intelligence capable of interstellar travel (or even interstellar communication)...humans aren't even really capable of it.
There might be billions of rockballs in the galaxy with life and intelligence at some level, maybe even up to the level of say a dolphin or a dog or even a chimpanzee on the high end. This might be the status today, or for the last hundred million years and the next hundred million. But those planets (and other orbs of lifebearing rock) aren't going to be sending spaceships our way anytime soon.
But let's suppose there's a million space capable intelligences spread out equally in the Milky-Way...what's the probability of them giving our particular system any interest whatsoever? The Drake equation is a fine estimate for the number of civilizations, but not for the probability that they'll contact us.
There might be billions of rockballs in the galaxy with life and intelligence at some level, maybe even up to the level of say a dolphin or a dog or even a chimpanzee on the high end. This might be the status today, or for the last hundred million years and the next hundred million. But those planets (and other orbs of lifebearing rock) aren't going to be sending spaceships our way anytime soon.
But let's suppose there's a million space capable intelligences spread out equally in the Milky-Way...what's the probability of them giving our particular system any interest whatsoever? The Drake equation is a fine estimate for the number of civilizations, but not for the probability that they'll contact us.