Using a popular internet game that traces the travels of dollar bills, scientists have unveiled statistical laws of human travel in the United States, and developed a mathematical description that can be used to model the spread of infectious disease in this country. This model is considered a breakthrough in the field.

“We were confident that we could learn a lot from the data collected at the www.wheresgeorge.com bill-tracking website, but the results turned out far beyond our expectations.”

Searching for a way to model the modern spread of disease became the focus of discussions among the co-authors: Theo Geisel…Dirk Brockmann and [Lars] Hufnagel. Following a conference in Montreal, Brockmann met with a friend in Vermont, a cabinetmaker, who showed him the internet game for tracking the movement of dollar bills, located at www.wheresgeorge.com. Participants can register a dollar bill, of any denomination, and monitor its geographic circulation.

The physicists were intrigued: Like viruses, money is transported by people from place to place. They found that the human movements follow what are known as universal scaling laws (from local to regional to long-distance scales). Using the game data, they developed a powerful mathematical theory that describes the observed movements of travelers amazingly well over distances from just a few kilometers to a few thousand. The study represents a major breakthrough for the mathematical modeling of the spread of epidemics.

Phew! Sure beats putting RFID tags on the backs of plague fleas.