Thought experiment: What would the world look like if every bit of land had the population density of Singapore?  With roughly 149 million square km of land on the planet, and a density of 6489 people per square km in Singapore, we get a world population of almost exactly one trillion.

What about a whole planet with the density of Manhattan?  That gets us to a little under 4 trillion souls.

If I have one complaint about the thought of Julian Simon, it’s that he spent too much time insisting that supplies and long-run growth potential were “infinite.”  These Zeno-style philosophical arguments are not necessary to sustain the radical but concrete hypothesis that in a few centuries, trillions of us might be prospering on planet Earth.  “It has to stop sometime” was as true when our population was 10,000 as it is today.  But as far as we can tell from the simultaneous rise of population and per-capita income, “sometime” is a long way off.