Grabby Aliens (2021)

Advanced aliens really are out there, and we have enough data to say roughly where they are in space and time, and when we will see or meet them. "Quiet" aliens don't expand or change much, and then they die. "Loud" aliens, in contrast, visibly change the volumes they control, and just keep expanding fast until they meet each other. We should believe that loud aliens exist, as that's our most robust explanation for why humans have appeared so early in the history of the universe. If loud aliens will soon fill the universe, and prevent new advanced life from appearing, that early deadline explains human earliness. "Grabby" aliens is our especially simple model of loud aliens, a model with only 3 free parameters, each of which we can estimate to within a factor of 4 from existing data. While we don't know the ratio of quiet to loud alien civilizations out there, we need this to be ten thousand to expect even one alien civilization ever in our galaxy.