Star Stuff...

Image Source: Brain Pickings

Topics: Astronomy, Astrophysics, Carl Sagan, Sociology, Urban Planning

"We are made by the atoms and the stars… our matter and our form are determined by the cosmos of which we are a part."

"We are made of star stuff." Carl Sagan

TECHNOLOGY REVIEW: Urban sociologists have long known that a set of remarkable laws govern the large-scale interaction between individuals such as the probability that one person will befriend another and the size of the cities they live in.

The latter is an example of the Zipf’s law. If cities are listed according to size, then the rank of a city is inversely proportional to the number of people who live in it. For example, if the biggest city in the US has a population of 8 million people, the second-biggest city will have a population of 8 million divided by 2, the third biggest will have a population of 8 million divided by 3 and so on.

This simple relationship is known as a scaling law and turns out to fit the observed distribution of city sizes extremely well.

Another interesting example is the probability that one person will be friends with another. This turns out to be inversely proportional to the number of people who live closer to the first person than the second.

What’s curious about these laws is that although they are widely accepted, nobody knows why they are true. There is no deeper theoretical model from which these laws emerge. Instead, they come simply from the measured properties of cities and friendships.

Today, all that changes thanks to the work of Henry Lin and Abraham Loeb at the Harvard-Smithsonian Centre for Astrophysics in Cambridge. These guys have discovered a single unifying principle that explains the origin of these laws.

And here’s the thing: their approach is mathematically equivalent to the way that cosmologists describe the growth of galaxies in space. In other words, cities form out of variations in population density in exactly the same way that galaxies formed from variations in matter density in the early universe.

Physics arXiv: A Unifying Theory for Scaling Laws of Human Populations
Henry W. Lin, Abraham Loeb