I think it is (among other things) the _sphere_. Imagine being a super AI. You know you might encounter _other_ super AI in the universe, so your priorities are

I think it is (among other things) the _sphere_. Imagine being a super AI. You know you might encounter _other_ super AI in the universe, so your priorities aren't to just spread in a uniform _sphere_. You want to target those places with the most resources that you can use most easily. So I expect even if an AI could spread at near the speed of light you'd expect to see them spreading non-uniformly, and therefor visibly. My deeper skepticism about this is the idea of a super AGI. I think we'll create AGI eventually and that they will likely be more capable than people. But I don't think that being more capable translates into being substantially more able to predict the future, manipulate the physical universe, make scientific discoveries, etc. There are plenty of problems that are hard regardless of how smart you are. I also kind of think that the fact that we don't see super AI gobbling up shit in our galaxy or elsewhere suggests strongly that mega-project scale AI just don't happen in this universe for some reason.