In which I post about a TL9 solar system

[AlexanderHowl]

The bottom line is that, whenever you predict current capability against future problems, you will always predict disaster. However, future capability should also be accounted for. Especially future capability we already know how to do.

I am quite familiar with the above concepts, and they do not matter for the purpose of the population figures given in Space. Arcologies are not sustainable population centers, they have enormous energy requirements, with the per capita energy requirements increasing as the population density increases. In addition, certain elements vital to agriculture and technology (copper, gold, iron, phosphorus, and silver just to name a few) are already near peak production for efficiency purposes, and the energy cost to increase their production increases exponentially.

For example, you would need an energy production of around 30 PW to support 30 billion people at TL9 average income (1 MW per person). The Earth only receives 170 PW of sunlight, so you would either need to blanket most og the world with solar panels to generate 30 PW or you need to add to the energy budget with fusion, orbital solar, etc. Either way, you dramatically alter the environment of the Earth. It actually becomes cheaper and more efficient to move people off the Earth, even with realistic technology, than to turn the Earth into a world city.