We’re not interested in the average number of alien civilizations, we’re interested in the distribution of probability over number of alien civilizations. SDO say that relying on the Drake Equation is the same kind of error. It’s not at all surprising that we see zero alien civilizations, it just means the coin must have landed tails. Since we see zero, that’s quite the paradox, isn’t it? Using our one parameter Drake Equation, we determine that on average there should be 5 billion alien civilizations. If it came up tails, He made none besides Earth. If it came up heads, He made 10 billion alien civilization. Sniffnoy’s comment on the subreddit helped me understand exactly what was going on, which I think is something like this: SDO’s contribution is to point out this is the wrong way to think about it. The actual Drake Equation is much more complicated, but most people agree that our best-guess values for most parameters suggest a vanishingly small chance of the empty galaxy we observe. So for example if we think there’s a 10% chance of each star having planets, a 10% chance of each planet being habitable to life, and a 10% chance of a life-habitable planet spawning an alien civilization by now, one in a thousand stars should have civilization. This is sometimes formalized as the Drake Equation: think up all the parameters you would need for an alien civilization to contact us, multiply our best estimates for all of them together, and see how many alien civilizations we predict. The Fermi Paradox asks: given the immense number of stars in our galaxy, for even a very tiny chance of aliens per star shouldn’t there should be thousands of nearby alien civilizations? But any alien civilization that arose millions of years ago would have had ample time to colonize the galaxy or do something equally dramatic that would leave no doubt as to its existence. (You may recognize these names: Toby Ord founded the effective altruism movement Eric Drexler kindled interest in nanotechnology Anders Sandberg helped pioneer the academic study of x-risk, and wrote what might be my favorite Unsong fanfic) I’m late to posting this, but it’s important enough to be worth sharing anyway: Sandberg, Drexler, and Ord on Dissolving the Fermi Paradox.
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