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?
Ems or other more efficient versions of living intelligence just put off the exponential malthusian day of reckoning by 100 years or a 1000 years or 10000 years. As long as you have reproducing life, its population will tend to or "want to" grow exponentially, while with technical improvements, I can't think of a reason in the world to expect them to be exponential.
I also wonder at what point speciation becomes inevitable or else extremely likely. Presumably in a world of ems with 10^N more ems than we now have people, and very fast em-thinking speeds restricting their "coherence length" (the distance over which they have significant communication with other ems within some unit of time meaningful to them) of perhaps 10s of km, we would it seems have something like 10^M civilizations averaging 10^(N-M) as complex as our current global civilization, with population size standing in as a rough measure of complexity. Whether ems want to compete or not, at some point you will have slightly more successful or aggressive large civilizations butting up against each other for resources.
In the long run, I think, exponentials dominate. This is the lesson on compound interest I take from Warren Buffett. Further, one of the lesson's I take from Matt Ridley's "Rational Optimist" is that the Malthusian limit is the rule and the last 2 centuries saw us nearly hitting it a few times, with something like the "Green Revolution" coming along in a "just in time" fashion to avoid it. Between what Hanson has to say and what Ridley has to say, and what Buffett has to say (about compound interest i.e. exponentials), it sure seems likely that in the long run Malthus is the rule and our last one or two centuries have been a transition period between Malthusian equilibria.