[AlexanderHowl]

An alternative idea would be to have a society where human civilization has abandoned the Earth (either because of ecological collapse or because of ecological preservation) and spread out across the Sol System. Even if the population of the Sol System was 20 billion, it would feel empty if it took an average of a month to travel between space colonies. If the average space colony possesses a population of 800,000, then the Sol System would possess 25,000 city-states.

Even if the majority of the space colonies (20,000) were located in the Main Belt, it would still seem rather empty, as they would occupy ~19 cubic AU (~64 trillion trillion cubic kilometers). With an average separation of nearly 19 million kilometers, each space colony would experience a more profound physical isolation than any settlement in human history. Each space colony would have to be self-sufficient, attached to a small asteroid that provides the raw materials for the systems that support its population, but it would likely trade only information, and even communication would be difficult with over a two minute delay in responses.