> 3 There is big cost or downside to galaxy-wide expansion that we don't get and that limits expansion, like travelling interstellar distances being far harder

> 3 There is big cost or downside to galaxy-wide expansion that we don't get and that limits expansion, like travelling interstellar distances being far harder than we imagine in practice. This is my thought. Without FTL travel you have to go the slow way. Probably much less than C thanks to the rocket equation. But in order to do this you need to build a spacecraft capable of surviving for centuries or longer with absolutely no outside support, not even solar power. But if you can build that you have effectively unlimited space in your own solar system. Why bothering to travel to a different solar system at that point? Maybe if you have used up literally all of the resources in your current solar system, but that's a multi-billion year process. So you might only need to make the trip once or twice in the current age of the universe. But even that seems less likely than just developing really good recycling systems. So the solution to the Fermi paradox is that by the time you have the tech to travel between solar systems there is no longer any need to do so.