McCormick Magazine

Modeling the complex systems of the world

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dirkMoney. Language. Infectious disease.

In our increasingly globalized world, tracking the movement within and boundaries of these huge, complex systems requires large-scale computing, interdisciplinary research, and a different way of thinking. Dirk Brockmann does that kind of thinking. A theoretical physicist who is now an associate professor of engineering sciences and applied mathematics at McCormick, Brockmann is applying his complex systems research to these global issues.

Brockmann started out wanting to use his modeling skills to help solve the world's most pressing issues — like infectious diseases — but he soon found that, like most complex networks, each issue he digs into leads to another, and another, and another. Nevertheless, his findings — illustrated as maps of networks — could have global implications.

Take infectious diseases, for example. In 2003 SARS made headlines when it infected 8,096 people worldwide, and researchers say that a larger-scale flu pandemic, where millions will be infected, is inevitable. "There are a lot of doctors and epidemiologists working on this," Brockmann says. "I'm looking at it from a mathematical epidemiology perspective. We're trying to develop a model to predict the spread of infectious disease worldwide."

Brockmann is examining data to figure out what conditions are necessary for infectious diseases to spread. Knowledge of those factors, along with high-performance computer clusters, can be used to simulate an infectious disease that spreads among 300 million people. "We can, on a very realistic scale, try to model an epidemic that has the same size as a real epidemic," he says.

In order to understand how disease travels, Brockmann must also understand human transportation networks. "These networks play an important role in the spread of infectious disease," Brockmann says. "So we're looking at how people travel in the United States and Europe and trying to find a theory behind human traffic. Then we can unravel the structures within these networks and explain them."

moneyOne way to track how people travel is to monitor how money travels. In a 2006 study, Brockmann used data from WheresGeorge.com — a site where users enter the serial numbers from their dollar bills in order to track their travels — to create a model to predict the probability of a bill staying within a 10-kilometer radius over time. That study caught the attention of a linguist in Pennsylvania, who contacted Brockmann to work on a new model — the spatial evolution of language. "English in the United States can be separated into various regions of dialects, and some of those dialect boundaries move over time while others don't move at all," Brockmann says. "It's not understood why those regions are the way they are, so we're trying to use what we know about travel patterns and our network theory tools to see if we can understand how these boundaries work."

This isn't the first time Brockmann has studied boundaries in the United States: He and his research group created a map of community boundaries based on human mobility, rather than the usual state-line boundaries of rivers, mountain ranges, or administrative lines. The map shows that some states, like Missouri, are essentially cut in half — likely due to two large cities that lie on either side of the state. Other boundaries are islands in the middle of states, as is the case with Santa Fe, New Mexico. "These boundaries might be better suited for developing mitigation strategies against epidemics," Brockmann says. "We're working on creating a similar map for Europe."

For his work, Brockmann collaborates with linguists, epidemiologists, ecologists, and other scientists from around the world. "It's fruitful because people have very different perspectives," he says. "It's only productive if the other person thinks that your viewpoint is as valid as theirs, and the other way around."

With so many irons in the fire, Brockmann is motivated by results that could potentially be useful for humanity. "I want to do work that is important, that involves pressing matters," he says. "It motivates me to do research on complex systems that will eventually improve life."

—Emily Ayshford