City dwellers have more contacts and accumulate them at a faster rate than those who live in smaller conurbations, say network scientists.
You don't have to spend long in a metropolis like New York, London, or Tokyo to sense the dramatic pace at which the locals live their lives. If you already live in one of these places, you'll get the sense by heading out into the countryside where life slows down.
But while this pace is easy to sense, it is notoriously difficult to quantify because of the practical difficulties in making the huge number of necessary measurements. Consequently, nobody has pinned down the nature of this "pace of life" or why it accelerates in cities.
Today, Markus Schläpfer at the Massachusetts Institute of Technology in Cambridge and a few buddies take a big step towards a better understanding of this phenomenon. These guys have found the first evidence that humans in cities interact more often and with a greater number of other people than those who live in smaller conurbations.
The researchers' result comes from the study of a vast number of anonymised telephone call records. They examined 440 million mobile phone calls made in Portugal over a period of 15 months and almost 8 billion landline calls made in Britain during a single month.
These guys worked out where each caller lived using the location of a mobile phone's most frequently used cell tower and a landline's local telephone exchange.
They then imagined that each call represents a link from one person to another and that the number of calls represents the intensity of this link. This allowed them to draw up a network of links between individuals from which they could see each person's set of contacts and whether the contacts are linked to each other. This is a measure of how tightly knit an individual's closest contacts are.
Finally, they ranked the results according to the size of the conurbation in which each individual lived.
The results show a clear power law. People who live in bigger cities not only have more contacts but accumulate them at a faster rate.
Schläpfer and colleagues say the results imply that during the 15-month observation period an average urban dweller in the Portuguese capital, Lisbon, accumulated about twice as many reciprocated contacts as an average resident of Lixa, a rural town.
"The results presented here constitute the first extensive empirical evidence of the acceleration of human interactions in cities," they say.
Of course, social scientists have collected all sorts of data pointing to a fast pace of life in cities. Various studies show an increase in cities for a wide range of bulk properties of a population—things like GDP, wages, patents, and violent crime. The legendary social psychologist Stanley Milgram showed that people even walk faster in cities.
But most of these studies suffer from problems such as a small sample size or an inability to connect bulk properties with the actions of individuals.
All that has changed with the increasing availability of huge data sets generated by individual actions and interactions—phone records, in this example. That gives social scientists an entirely new way to study humanity.
There are still challenges ahead. Schläpfer and co show that the pace of life accelerates in cities in terms of the amount of interaction humans have with each other but it doesn't show how or why this happens. What set of events causes a person in Lisbon to accumulate twice as many contacts as a person in Lixia?
And of course, the pace of life is just the tip of the iceberg. On this blog, we've looked at similar approaches for studying human reproductive strategies, the emergence of good and bad behaviour, and the new science of culturomics.
Statistical physics has worked wonders in the last few hundred years, producing magnificent insights into the bulk properties of matter through the science of thermodynamics. The bigger question here is whether a similarly grand approach to humanity will produce just as spectacular insights into the bulk properties of society.
There's only one way to find out!
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