Space isn't that big at all, actually. In a couple of thousand years we would be able to expand at a rate of almost the speed of light: go to a neighbouring sta

Space isn't that big at all, actually. In a couple of thousand years we would be able to expand at a rate of almost the speed of light: go to a neighbouring star, build a colony in about a century, go to the next star. You'd spread out over a significant portion of the galaxy in only a few aeons. It's not the gulfs of space that are huge, it's the gulfs of time that separate us. Stars' ages differ in billions of years. Maybe the total lifetime of the galaxy will harbour millions of civilizations all at some point, but rarely any at the same point in time?