Even in our universe, the numbers get really big, really fast (on astronomical timeframes). Given our current science and not that much more technology, just our solar system could support quintillions of humans.
Multiply that by billions of solar systems – we don’t really need inhabitable planets – in the galaxy and potential population numbers go crazy. If it’s up to us to populate the galaxy, it will take a few tens of millions of years at sublight speeds, but that’s a tiny fraction of a star’s lifetime.
Expanding out to a universal scale, that gets multiplied by trillions of galaxies. Given current science, it’s unlikely that we’ll get to many of them, but “a few” is certainly possible, if very slow.
Now make it a multiverse. If individual universes are getting gobbled up into it, even relatively slowly at one every billion years, the population potential is gargantuan. “Finite but unbounded” is pretty much all one can say.
My handwavium is that the energy gathered by stopping the expansion of a universe is sufficient to system-ize the thing. I’m also going to use that as the excuse to fall back to Newtonian physics (so teleportation can work). This means red-shifting will stop and the universe will start blue-shifting, relatively speaking. In 14.5 billion years, the entire universe will be visible. Probably not enough to turn the night sky white, but certainly much brighter than it is now.
I doubt my story will last that long – although it would make for a very long series. But, our universe is not the first. At one per billion years, if we’re number 62 (which is my current thought), that means the first 45 or so (depending when in their lifecycle they were system-ized) will have already gone through this.
The original civilizations, let alone individuals, may be long gone, but there will still be people there doing stuff – including reproducing. At a 100 billion years old, our universe will still be producing new stars, so it seems safe to assume resource constraints are not an issue. K3 civilizations exist. The system, itself, is probably K4 or even K5. At that point, it doesn’t really matter. The amount of resources is insane.
Even if “no one” cares about our universe, let alone Earth, if 0.0000000000000000001% are interested, that’s several billion people descending upon our universe. Some of them are bound to end up on Earth.
This comes up because in several multiverse series, Earth is special and attracts interest. It really doesn’t need to be. There are so many people out there that even uninteresting things will be interesting to someone, which means some millions of ones, at least. Think of it this way: In a solar system populated by a quintillion humans, how many of them will have Underwater Basket Weaving degrees? It’s an astonishing large number. Even now it’s a big number and we’re hardly a post-scarcity civilization.
Marked Up 