In essence, they arrive at the sensible conclusion that cities are valuable because they facilitate human interactions, as people crammed into a few square miles exchange ideas and start collaborations. “If you ask people why they move to the city, they always give the same reasons,” West says. “They’ve come to get a job or follow their friends or to be at the center of a scene. That’s why we pay the high rent. Cities are all about the people, not the infrastructure.”
According to the data, whenever a city doubles in size, every measure of economic activity, from construction spending to the amount of bank deposits, increases by approximately 15 percent per capita. It doesn’t matter how big the city is; the law remains the same.
After a city doubles in size, it also experiences a 15 percent per capita increase in violent crimes, traffic and AIDS cases. (Of course, these trends are only true in general. Some cities can bend the equations with additional cops or strict pollution regulations.) “What this tells you is that you can’t get the economic growth without a parallel growth in the spread of things we don’t want,” Bettencourt says. “When you double the population, everything that’s related to the social network goes up by the same percentage.”
The historian Lewis Mumford described the rise of the megalopolis as “the last stage in the classical cycle of civilization,” which would end with “complete disruption and downfall.” In his more pessimistic moods, West seems to agree: he knows that nothing can trend upward forever. In fact, West sees human history as defined by this constant tension between expansion and scarcity, between the relentless growth made possible by cities and the limited resources that hold our growth back. “The only thing that stops the superlinear equations is when we run out of something we need,” West says. “And so the growth slows down. If nothing else changes, the system will eventually start to collapse.”
How do we avoid this bleak fate? Constant innovation. After a resource is exhausted, we are forced to exploit a new resource, if only to sustain our superlinear growth. West cites a long list of breakthroughs to illustrate this historical pattern, from the discovery of the steam engine to the invention of the Internet. “These major innovations completely changed the way society operates,” West says. “It’s like we’re on the edge of a cliff, about to run out of something, and then we find a new way of creating wealth. That means we can start to climb again.”
But the escape is only temporary, as every innovation eventually leads to new shortages. We clear-cut forests, and so we turn to oil; once we exhaust our fossil-fuel reserves, we’ll start driving electric cars, at least until we run out of lithium. This helps explain why West describes cities as the only solution to the problem of cities. Although urbanization has generated a seemingly impossible amount of economic growth, it has also inspired the innovations that allow the growth to continue.