Human Population and Moore's Law
Moore's Law states that CPU processor speeds will double every 18 months, and has been remarkably in effect since the early 1980's. Anyone living in the 1980's would tell you that it was very unlikely or impossible to meet that trend, and it has continually surprised us that we have been able to meet it at all. 1994. 1998. 2003. Still ticking.
I believe that a similar principle applies for the earth's ability to sustain life with the use of our technology. Nicholas Nickelby was a story from a hundred or two years ago that commented on the crowded state of London. At the time it must have contained over a million people. Today it contains more than 7 million people. Who thought it possible? Indeed, with ancient technologies it would be impossible to meaningfully sustain 7 million people on 50-60 square miles. But today it is commonplace, and despite certain problems, profitable.
We also have vast stretched of basically uninhabited land out there in the world. We crowd around cities on riverways and ports and train old track crossings because of our fragile social systems of money and labor. As our technology and society advances, we will be able to populate the planet further than this, and further than that. Overcrowding is an artificial condition. Total population X social/technological desperation = crowding. Eventually, I see no problems with the planet, and the solar system in particular, sustaining 20 billion people.
New systems of agriculture and power generation, water purification, transportation, industrial pollutant abatement, and social/civil service generation and education can make a planet with 20 billion people on it feasable, and ecologically sound. Even
pleasant. For technological details not specifically formatted to maximum population, examine the home links found in the right side toolbar.