Web Exclusives: Alumni Spotlight

Cornell mathematician Steven Strogatz '80 has been at the forefront of the movement to turn "sync" into the next hot scientific discipline.

Photo by Dede Hatch

October 8, 2003:

Working together
Steven Strogatz '80 pioneers new science of sync

Gaze out at a suburban lawn at dusk, and the fireflies you see will light up haphazardly: As soon as you see a flash out of one corner of your eye, it disappears and another one appears somewhere else.

Like most of the estimated 2,000 species of fireflies around the world, they don't flash in unison. But a handful of firefly species do, including Photinus carolinus, which lives near an abandoned cluster of cabins called Elkmont, on the Tennessee side of the Great Smoky Mountains National Park.

Now, only a decade after scientists first took note of them, these unusual insects have become the most popular symbol of an emerging field called "synchrony," or, more commonly, "sync." And Steven Strogatz '80, Cornell University mathematician, has been at the forefront of the movement to turn "sync" into the next hot scientific discipline.

Synchrony appears throughout the natural world. It is most obvious in schools of fish turning suddenly in unison, or birds wheeling through the sky in formation, or in the perfectly timed chirping of crickets. At Elkmont, for two to three weeks every June, groupings of hundreds of male fireflies flash together four to eight times, with a brief pause between flashes. Then the flashing stops for six to 10 seconds before the cycle begins once again. The display starts at dusk and lasts for hours.

"It's like a wave as it goes up the hill," says Rebecca J. Nichols, a National Park Service entomologist. "Once the first one starts, they all follow."

Regular users of the cabins had noticed, and enjoyed, the phenomenon for years. But until the early 1990s, scientists had believed that the only truly synchronous fireflies were species native to Southeast Asia that flashed in unison while resting on riverbanks.

That changed in 1992, when Elkmont regular Lynn Faust saw an article about Strogatz's work on synchrony. Strogatz was studying synchronous patterns in nature, and the article mentioned fireflies — but not those at Elkmont. So Faust described their behavior to him.

Strogatz put Faust in touch with Jonathan Copeland, a behavioral neurophysiologist at Georgia Southern University who specializes in fireflies. Along with Andrew Moiseff of the University of Connecticut, Copeland had studied synchronous fireflies in Southeast Asia the previous summer.

Since then, Copeland and Moiseff have returned annually to Elkmont, hoping to understand both the how and the why of synchronous flashing. The how, as best they understand it, is that the males synchronize by watching other males. The researchers demonstrated this by experimenting with "artificial males" — computer-generated flashes — and by setting up pairs of fireflies in a chamber. When blocked by an opaque barrier, the paired insects flashed independently, but as soon as the barrier was removed, they flashed in sync with the computer.

As for why, several theories have been suggested over the years. The Leading, though not yet proven, explanation is that females are likeliest to mate with males that flash earliest. The inevitable result of this fierce competition, the theory goes, is that every firefly ends up flashing simultaneously.

As a mathematician, Strogatz was less interested in the mechanics than in the fact that they behaved synchronously at all.

For him, the firefly served as the perfect poster child for sync. When Strogatz published Sync: The Emerging Science of Spontaneous Order (Hyperion) earlier this year, he put fireflies on the cover.

Though the book is filled with difficult mathematics, it is designed to introduce a lay audience to the many systems that exhibit spontaneous synchrony.

"It's a theme you see a lot in biology," Strogatz says, and not just in birds and fish and crickets. Heart cells beat in synchrony; women who live or work together may find their menstrual cycles coinciding due to subtle chemical communications; and certain kinds of cicadas emerge in unison every 17 years.

Odder still is the synchronous behavior often seen in inanimate systems: lasers, electrical grids, quantum mechanics, flows of automobile traffic.

"What I find striking about these phenomena is that they illustrate the theme of self-organization," he says. "There's nothing in the environment — no lightning bolt, no external cause — that tells them to. It emerges automatically."

The fact that we see only one side of the moon as it circles the Earth is a form of sync, stemming from the stabilizing tidal forces exerted by the Earth on the moon. So is the phenomenon, discovered accidentally in 1665, that two clocks in the same room may synchronize their pendulum swings as they react to each other's vibrations.

"Mindless things can synchronize by the millions," Strogatz says. "It doesn't take a mind, or even have to be alive. Simple laws could lead to groups being in sync. It's counterintuitive, because the usual thinking was that things get more disordered over time."

Sync is merely the most recent multidisciplinary theory to create a public stir, following the popularization of chaos and complexity theory in the 1970s and 1980s. But while many researchers are looking at aspects of sync individually, it has taken time for a unified discipline of "sync" to jell.

One reason may be the complicated mathematics that describes synchronous behavior. Another reason may be the intense specialization of much contemporary scientific research, which tends to discourage interdisciplinary forays.

John Hopfield, a professor of molecular biology at Princeton who once studied similarities between neurons and earthquakes, said that "synchrony is not, in my opinion, likely to become a field of science, just as calculus is not a field of science. But ... the better it is understood mathematically, the more likely we are to be able to understand, control, and utilize synchronization effects in the real-world systems of science and engineering."

And Philip J. Holmes, a professor of mechanical and aerospace engineering at Princeton who calls himself "an old-school disciplinarian," adds that while multidisciplinary work can be "useful and illuminating, it does not replace the hard, detailed, often tedious science that still has to be done, often using the usual disciplinary tools." Yet even Holmes notes that he and his colleagues are using applied mathematics to understand some aspects of synchronized pulses in a part of the brain stem that helps oversee cognitive processing.

By focusing on complex and far-flung interactions, sync may help scientists make progress on such conundrums as the survival of stressed ecosystems, the evolution of global climate change, and the operation of the international economy. These questions, he suggests, may be impervious to science's most familiar method of analysis--looking at ever-smaller units.

Strogatz himself is beginning to apply his background in mathematics and sync to explore the mysteries of cancer. "Bad genes explain some cases" of cancer, he said, "but others are not explainable, and they seem to have something to do with the choreography of chemical reactions going wrong. So I want to be helpful, but I'm not sure exactly how."

By Louis Jacobson '92

Louis Jacobson, a staff correspondent at National Journal magazine in Washington, writes frequently about science. A different version of this article appeared in the Washington Post.