You've touched on something that's been tickling at the back of my mind for a while, about the role of differentials in free-market economies--"buy low, sell high", or "economic energy potentials" in quasi-physics terms.

It's the nagging suspicion that much of our first-world prosperity has been created in large part by an artificial subsidy that won't last forever. It's been highly profitable to be able to extract raw materials cheaply from around the world, and bring them to America by way of long and elaborate supply networks. The differential standard of living between us and our suppliers made the deal seem attractive to our suppliers, for a long time. But as their own standard of living rises their expectations rise, and we're going to start paying more and more for raw materials. As the playing field levels we're likely to see our prosperity evaporate.

That brings me to the question of where that level would be. I guessed 16th century because the laws of supply-and-demand lead to inflation whenever more and more people compete for scarce goods. You've heard of the estimate that Americans (and other First-Worlders) consume about 22 times the resources as people living in the Third World. Jared Diamond calculates that raising the living standard of everybody else to First World levels will have the net result of the entire human race consuming 15 times the quantity of resources that we do today.

In other words, the world today would hold the equivalent of about 100 billion people if everybody lived at American standards. By mid-century, when population is forecast to level off at about 15 billion and, not so coincidentally I think, countries like China have completed their modernization programs, you're talking about an effective world population on the order of 225 billion people.

The Earth doesn't have that kind of resources to give. Instead, all of us will be able to live no better than our share of the pie cut 225 billion ways, and to tell ya truth, I think I was being optimistic when I estimated a 16th century peasant standard of living.

In the same book, Diamond addressed the answer you've given me before on this subject: "Technology will provide". But doesn't the scope of the problem shake your faith even a little bit? Against a problem that big, it seems to me that we're talking about a technology indistinguishable from magic. We're almost talking about living off sunlight and folding space to give everybody room to turn around!

I too come back to space industrialization, although not as the solution, but at least as the lifeline. Earth's going to get damn unpleasant over the next few decades, and it's necessary that at least a few of us establish another place to live. That'll happen as a side-effect of a desperate attempt to hold off the inevitable by mining the Solar System to try and save Earth. And maybe we would succeed in saving Earth, and then we'd have the space infrastructure as a bonus. So creating the proverbial space-faring civilzation is a win-win in my view, and I know I'm preaching to the choir.