Complexity is Cool

Some of my favorite sessions at the APS March meeting are sponsored by the Group on Statistical and Nonlinear Physics (GSNP). It’s an odd branch of physics that addresses things like the dynamics of the stock market, connections between the neurons in your brain, the information storage in DNA, and the motions of animals as they swim, fly and run.

I like the field so much, that a complexity paper by Albert-László Barabási on the inaccessible portions of the Internet inspired me to write a pulp science fiction book called The Dark Net.

Barabasi was here again this year to tell us some things he’s discovered about the patterns that describe human activity. Several of his students were here to report on cell phone viruses and disease networks. Hmm, I think a Dark Net sequel may be called for.

Another GSNP paper that caught my attention is Dirk Brockmann’s analysis of the flow of dollar bills in the US. He got his data from the Where’s George web site that lets people track dollar bills by entering serial numbers in a database.

It’s amazing what you can get from ten million or so bits of information about bills. For example, the Where’s George data shows how closely people in different parts of the country are connected. Folks in western Pennsylvania seem to exchange lots of money with people in Ohio, but not much with people in eastern Pennsylvania. The easterners instead pass money back and forth with people living in New Jersey, New York, Delaware and Maryland. And even though the state of New York butts right up against New England, very little cash crosses the boarder with Vermont. The money trail shows that the New England states are tight, with more cash traveling hundreds of miles within the region than leaking just a few miles into surrounding states.

Brockmann’s work makes me wonder if we should redraw the state borders to take account of the way people associate. New England would be one big state, and I could vacation in the superstates of of WestVirginaPennsOhioAtucky, CaliAriZonaMexVada, or Texas (Surprise, surprise – Texans don’t seem to be tight with anyone else, according to Where’s George data, even though we’re all welcome to stop by).

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