ErikH2000 wrote:
Well, there is one simple thing I've concluded from this: There are really two big questions here, and once you have a decent answer for both, the first question can be answered.
A. What is the maximum number of years from now that the Earth could remain human-habitable?
B. What is the maximum amount of living people you can pack onto the planet at one time?
The answer to my question is A * B * 1/18, right? Sure, you could quibble and say that the earth couldn't possibly be maximally populated tomorrow, but if the answer to A is measured in billions of years, it can't matter to the already sloppy guess if it takes one or a hundred millenniums to ramp up to max pop.
The problem with this is that it seems that A and B are not independant of each other, but rather you have to ask 'what is the longest the earth can remain human-habitable (A) under the stress of population (B)?', and then find the product maximizing this.
For example, say the earth could sustain 700 billion humans for a year, but this would convert all breathable oxygen into C02, causing a dieoff of all but a few humans in atmosphere processing domes of some sort. Or we could sustain 70 billion humans for 1000 years, but at the cost of rendering all species extinct within those thousand years, with humans following shortly thereafter. Or we could sustain 7 billion humans for 5,000 years until an alien invasion fleet arrived and we just weren't populous enough to raise an army to defend against them.
None of these scenarios are meant to be serious guesses, but the point is the middle population figure would get the best results despite being an order of magnitude smaller than the max possible guess, and the variables really do seem to interact quite a bit.
Also, I'd say the hard limit here isn't the time it will take the sun to burn out, but the time it will take for evolutionary pressure to change our descendants into something that would not reasonably be considered human, in the same way we don't consider a bird to be a reptile. I don't have any good guess for how long this would take, and through out to very broad guess that it would be at least 10 million years, but probably not over 100 million, depending how diffrent they would need to be to no longer be considered human. I'm not talking 'people with a bigger head' or something like that, but if something fundamental such as abandoning language, or developing into a new class as fundamentally diffrent from mammals as mammals or bird are from reptiles happens, I don't think its clear at all we should be calling the result human, it would be something new.
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Now I will repeatedly apply the happy-face rule"
