I might need a better title (It has now been updated), but here goes, anyway:
I've been considering this for a while now. Suppose we reach a point where we can live for centuries, maybe even millenia, then how do we balance? Even assuming we're as efficient as possible, there's a limit for how much resources we can have, meaning an artificial limit at the amount of people that could exist at any given moment even if we explore what we can of the galaxy and use any avaliable resource. There would have to be roughly the same rate of births and deaths in a stable population.
How would this be achieved? Somehow limiting lifespan, or children, assuming it's available to a majority? Or would this lead to a genespliced, technologically augmented and essentially immortal elite that the poor, unaugmented ones would have no chance of measuring up to? I'm sorry if this has already been considered, I'm very uneducated on the topic. If it has, could someone maybe link an analysis of the topic of lifespans and the like?
I think It's a biggish problem to solve.
The first thing that makes it easier is that I see no reason we ought to increase the number of people very much. I think N billion is enough of a party already. Once we all know each other, maybe we can talk about making more. (for the people who are still alive)
Of course that doesn't make the problem go away. If we want to grow as people continuously, we will eventually hit limits. Especially since we might decide that exponential growth is the only acceptable thing.
We might have to accept that there is a non-infinite amount of utility in the universe. That's no reason to give up tho. We should still make sure we at least hit the maximum possible.
See the fun theory sequence specifically this one for exploration of these issues.
If you are part of a group that wants to grow slowly and there are even two intelligences out there who are not on board with your program, your group will have to have a CEV which kills off the dissenters. Otherwise, "compound interest" growth rates of the dissenters will turn your slow-growers into a footnote, a vanishingly small "also-ran" in the evolution of transhumanists.