Apr 14, 2019 I Sequoyah Kennedy

The Way Cities Grow on Earth Mirror How Galaxies Are Formed in Space

People are a lot more predictable than we like to pretend. Sociologists have a set of laws they use to predict how large groups of people will behave—how populations shift, how likely two people are to become friends, how population distribution between cities in a given country will shake out. One such law is called Zipf's law which predicts the populations of cities in a given country with spooky accuracy. Zipf's law says that populations of cities will be inversely proportional to the city's rank. If the most populous city in a country has 10 million people, the second most populated city will have a population of 10 million divided by two, the third most populous city will have a population of 10 million divided by three, and so on and so on until you get to the city ranked 10 millionth on the list which is just a dude in a treehouse.

Zipf's law has been accepted as true by sociologists, but until now there was no theoretical framework for why. It was simply based off what sociologists have observed. Well, now there's a potential answer for why: it was written in the stars.

Or, more accurately, galaxies. A recent paper by Henry Lin and Abraham Loeb at the Harvard-Smithsonian Centre for Astrophysics in Cambridge proposes that there is a grand, unifying principal behind all scaling laws—like Zipf's law—based on the way galaxies formed at the beginning of the universe. They write:

“We treat the population density as the fundamental quantity, thinking of cities as objects that form when the population density exceeds a critical threshold. The situation is therefore conceptually and mathematically analogous to the formation of galaxies in the universe.”

galaxy cities how galaxies are formed 570x416
This is just a big old space-city.

Using publicly available population data and the decades of cosmological work done studying galaxies, Lin and Loeb showed that the models that determine the spread and makeup of galaxies can be used to predict human population scaling. Each time they used their galaxy-based model to predict population changes, they came to the exact equations that were already present in sociologists' scaling laws.

And it wasn't just city size. They found a galactic explanation for the laws governing whether two people become friends, the spread of sexually transmitted diseases, and other complex human interactions. They write:

”We derive a simple statistical model that explains all of these scaling laws based on a single unifying principle involving the random spatial growth of clusters of people on all scales.”

city galaxy scaling laws unified theory 570x283
And this is just a little people-galaxy.

It's pretty wild, but it's hard to be surprised by it. After all, we're made of star stuff, and whether you're a person or a galaxy, math is math. And while this is hard science, it's a principal that's been espoused for very long time by people that don't really understand what they're saying: as above, so below. The math that governs galaxies is the same math that governs human populations. I don't know if I'm awe-struck by that, or depressed. Maybe a little bit of both.

Sequoyah Kennedy

Sequoyah is a writer, music producer, and poor man's renaissance man based in Providence, Rhode Island. He spends his time researching weird history and thinking about the place where cosmic horror overlaps with disco. You can follow him on Twitter: @shkennedy33.

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