The Optimum Quantity of People

Ted Turner, billionaire founder of CNN, has stated that the target for world population should be five hundred million, or three percent of the current number. But to achieve that it would be necessary to enforce a one child policy for multiple generations. Ted Turner has five acknowledged children and thirteen grandchildren. It would seem, therefore, that the only decent thing for Ted Turner to do is to off himself without further delay. 

Elon Musk, who has ten acknowledged children, advocates for a huge increase in human population, and sees no consequent problem of overcrowding because folks can migrate to Mars -- after you Elon.

Mars is a Hell of a place, literally. Among the problems for any human resident there is a very thin atmosphere, with an atmospheric pressure only 2% of that on Earth. And what little air there is, is unbreathable, consisting mainly of carbon dioxide. 

The thinness of the Martian atmosphere is due to the planet's lack of a magnetosphere to deflect the solar wind, a stream of charged electrons and protons emitted by the Sun that continually strip away the Martian atmosphere. Because of the ionizing properties of the solar wind, humans resident on Mars would need to live in caves, which is probably the best place anyhow since it's darned cold there, with an mean surface temperature  around 50 Celsius below zero. 

Central Park, Manhattan Island, New York

In fact, there's no imminent need to remove people from the face of the Earth despite the growing population. With today's World population of eight billion, there is around 1.4 hectares of habitable land per person, so even on a trillion-person world, there'd still be 110 square meters of habitable land per person, which is twice the area per person in present-day Hong Kong, and more than three times the area per person in the New York suburb of Manhattan -- and that's including Central Park. 

Compared with today's world, those densities seem high, but with a population accomodated in high-rise buildings, there would still be plently of unbuilt space. For example, the entire current population of Manhattan could be accomodated in just 444 buildings 40 meters square at the base and 100 stories tall. That would leave 95% of the land area as open space, for farms and parks. Another option would be to accomodate the entire population of Manhattan in one 16-mile-high buildings, as envisaged by Frank Lloyd Wright.

As to why we'd want so many people, it's been argued that with more brains we have more brilliant ideas leading, presumably, to a greater GDP, and thus perhaps to even more people. Some people, I suppose, like to live in a humming, buzzing, super busy place. My own preference would be a return to the world in the year of my birth when global population was barely two billion, or one quarter of the present crowd.