Do Cities Work Like Stars?


Cities have been compared to living organisms, machines, river networks and insect colonies. Instead, suggests a new study, urban centers are more like stars, fusing human connections as if they were hydrogen atoms.

But only sort of. Using mathematical equations to synthesize mounds of data, a researcher concluded that cities are vastly more complex and open-ended than any system in nature.

Still, by developing a unified theory of urbanization that explains the essence of how cities grow and function, the hope is to help policy-makers and planners design better, more efficient cities that prioritize social connections and induce innovation.

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“At the center of a star, the core is so dense that nuclear interactions take place and as a result, light comes out. And basically, the light that comes out of a star is brighter and reactions are faster the larger the star is,” Bettencourt said. “That’s a little bit like what cities do, too. It’s mathematically different, but the larger the population is, the faster the rates of social interaction.”

“Stars are nuclear reactors and cities are a different kind of reactor,” he added. “They are social reactors.”

Cities have been a source of philosophical fascination since the time of the ancient Greeks. Even Aristotle wrote about the purpose of cities. He observed that people are more political than any other animal and he explored the virtue of public life.

For the past decade, Bettencourt and colleagues have taken a more systematic and quantitative approach to understanding cities by gathering data from a wide variety of disciplines, including economics, urban geography and social psychology.

Instead of focusing on form and what cities look like, Bettencourt said, he was more interested in function and how cities work.

Among other details, he considered land-use, area of roads and other aspects of infrastructure. He collected information on electricity consumption, pipe volumes, and measures of innovation, such as numbers of patents and people in creative professions. And to round out the big picture, he factored in incidences of disease, violence and crime. Then, he crunched the numbers.

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