Emerging Complexity

One of the most fascinating scientific developments of the past 20 years has been the emergence of the field of complexity.  With the advent of computers, scientists can now model massively complex systems – many of which tend to form from remarkably simple interactions.

A case in point was revealed in a New York Times article on cellphone tracking.  The article summarized a recent letter to Nature magazine, understanding individual human mobility patterns (PDF).  Previous studies of human mobility had used the sighting of banknotes in the same geography (via Where’s George) as a proxy for human mobility.  The conclusion: humanity’s movement was random, following a fat-tailed Levy distribution (a lot of movements of short distances but more long distance movements than you’d expect).

However, the new study actually tracked people’s movements based upon their cellphones (data was anonymized and from a European provider who is required by law to track).  What’s the new conclusion: humans don’t actually travel too far on average and our movements are actually highly predictable (Not too surprising given how much of your time is spent at work or home).

How do you reconcile the random movement of money with the predictable movement of humans?  Simple “dollar bills diffuse, but humans do not” – the dollar bills do not travel with each human daily, rather are passed on.  As a result a bunch of humans who do very predictable things can cause apparently random patterns to emerge in the movement of money.  This is a classic example of complexity: a series of simple actions create a ridiculously complex pattern at an aggregate level.

Fascinating science and kind of makes me want to be an undergrad again.