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How 'six degrees' can connect the world – and scientists

Robert Barker/University Photography
Steven Strogatz, Lars Backstrom '04, Ph.D '09, Michael Macy, Jon Kleinberg and Duncan Watts Ph.D '97 explore how networks can explain a wide range of phenomena at the Charter Day Weekend panel, “Six Degrees of Separation,” April 26 in Bailey Hall.

The interdisciplinary culture of Cornell has fostered collaboration between a mathematician, a computer scientist and a social scientist that reveals how networks explain a range of phenomena in fields from biology to electric power transmission to politics. Their work has helped bring about a revolution in social science, and might even lead to a better understanding of the causes of cancer.

All this was explained in the Charter Day Weekend presentation, “Six Degrees of Separation,” April 26 in Bailey Hall with professors Michael Macy, Steven Strogatz and Jon Kleinberg; and computing and information science alumni Lars Backstrom ’04, Ph.D. ’09, now at Facebook, and Duncan Watts, Ph.D. ’97, now with Microsoft Research. John Guare, who wrote the play “Six Degrees of Separation,” participated via a video clip in which he expressed amazement at how that phrase has become part of the language.

Introducing the panel, Macy, the Goldwin Smith Professor of Sociology, invoked a Charter Day theme by pointing out that the university started with the telegraph network created by Ezra Cornell. Scientists were studying networks even then, but a new era arose from curiosity about how crickets chirp in time and fireflies blink in unison. It seems they network with the flock through their near neighbors. So how might 7 billion people on Earth be connected?

This led to the famous six degrees experiment in which Harvard professor Stanley Milgram gave a random group of people envelopes and asked them to pass them on to someone who would know someone who would know someone… in a chain leading to the addressee. Some messages arrived quickly, some took many steps, but the average was six steps. Strogatz, the Jacob Gould Schurman Professor of Applied Mathematics, and Watts developed a theoretical model that explained what happened.

Out of this grew advances in networking theory, and how it applies to the Internet, the power grid, neurons in the brain and more. Much of this is explained in “Networks, Crowds and Markets: Reasoning About a Highly Connected World” by Kleinberg, the Tisch University Professor of Computer Science, and David Easley, the Henry Scarborough Professor of Social Sciences.

A new application, Strogatz reported, lies in the study of how a network of enzymes and other proteins interact in the process of cell division; cancer happens when that process goes wrong. The one gene that seems to be responsible should be seen as just part of an intricate choreography.

Discussion turned to the impact of computing on social science. “Some of the best social science at Cornell is being done by computer scientists,” Macy said.

It’s an exciting time for social scientists, Strogatz added, because observations that used to be made on a roomful of college sophomores now can be extended to thousands of people in online social networks. “We now have terabytes of data,” he said.

Finally, the panel discussed what it is about Cornell that makes collaborations like theirs happen. It begins, Strogatz said, with admitting your ignorance about fields outside your own, but then “It’s something about Cornell and Ithaca.” Perhaps, Kleinberg suggested, it’s about meeting your colleagues at daycare or while walking the dog.

The six degrees experiment is re-created in a documentary film, “Connected: The Power of Six Degrees,” featuring Strogatz and actor Kevin Bacon, who has been in so many movies with diverse casts that he can be used to make up a six-degrees chain between almost any two other actors. The film, sometimes referred to as “How Kevin Bacon Cured Cancer,” is showing on CornellCast.

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Joe Schwartz