September 15, 2003

Understanding the Science of 'Sync'

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When the lights went out in Manhattan during last month’s blackout, no one could say why the world’s largest machine–the North American power grid-had failed. With mass transit crippled, many New Yorkers found themselves plodding home on foot, and as thousands of pedestrians made their way across the East River, the Brooklyn Bridge began to sway.

Meanwhile, the lights were still on in the remote jungles of Southeast Asia. Every evening, hundreds of thousands of fireflies that occupy the thickly forested riverbanks commence a rhythmic, synchronous flashing–a visual symphony that stretches for miles along the waterfront. At first glance, these incidents may appear completely unrelated.

Now enters the science of sync. In a recent book, Sync: The Emerging Science of Spontaneous Order, Prof. Steven Strogatz, theoretical and applied mechanics, explains how order emerges in far-flung systems ranging from populations of flashing insects to power grids to pedestrians crossing bridges en masse.

“The real question here is where does the order come from. I’m not sure if I would call it a new science or rather a combination of existing sciences,” Strogatz said.

Strogatz maintains that sync is a new way of looking at populations and how the individual parts interact. “It’s interesting because science has always been about taking things apart but this is about putting things back together and observing the behaviors that you wouldn’t have seen just by looking at the smaller pieces,” Strogatz said.

Strogatz explained that one of the features of sync is its ubiquity.

In biology, examples include the cluster of pacemaker cells in the human heart that, like some fireflies, pulse simultaneously functioning as a metronome for the heart. Neurons demonstrate a similar burst of cooperation to aid in the recognition of a familiar face, Strogatz said.

In 1989, Strogatz proved how certain species of firefly can coordinate the flashing of a large population simply by keeping time and observing the flashes of their nearest neighbors.

“Can perfect synchrony emerge from a cacophony of thousands of mindless metronomes? … The answer is yes. Not only can it work — it will always work, under certain conditions,” Strogatz writes.

Western travelers to Southeast Asia had been baffled by the firefly phenomenon since the early 17th century, Strogatz explained. The massive coordination of unintelligent insects had been the subject of conjecture for centuries and the attempts to understand their collaboration has served as the catalyst for sync’s quiet revolution.

Synchrony can also play a role in human affairs. Strogatz described an experiment in which sweat from a woman who was known to be a “powerful synchronizer” was used to align the menstrual cycles of other women with her own. In this way, subconscious chemical signals can give rise to menstrual synchrony among women.

Sync also touches on areas of physics and engineering where photons and electrons synchronize to produce lasers and semiconductors. Synchrony can also arise where biology and engineering interact.

Such an interaction took place when London’s Millennium Bridge was opened in June 2000. As thousands of pedestrians marched across the bridge, the resulting vibrations caused foot traffic to synchronize and the bridge began to shake violently. According to Strogatz, a similar phenomenon could have been responsible for the uneasiness experienced by those on the Brooklyn Bridge during the blackout exodus.

The power grid is also subject to the whims of sync. “There are two aspects of the power grid that relate to sync. First, all generators in the grid rotate at the same frequency and in phase due to a self-organizing tendency in the grid. With the blackouts, there is also the effect of cascading failures that spread rapidly across the grid,” Strogatz said.

Sync may even be applicable to some social phenomena. “We see this in things like flash mobbing, fads and buying and selling patterns in stock markets,” Strogatz said.

One of the main principles at the heart of sync is connectivity — the relationships between the components of a system or the individuals in a population.

A continuation of this idea is “Small World Theory,” known more commonly as six degrees of separation. The idea is simple. If you select two random people anywhere in the world, you can connect them through a chain of six or fewer personal relationships. This is not just a theoretical curiosity, but now a proven fact.

“When e-mail was used to find a target person through chains of acquaintances, it was found that when people participated instead of discarding the e-mails as spam they were able to complete the chains in five to seven steps. This is the first real, large-scale confirmation of the six degrees idea,” Strogatz said.

The study, which focused on 18 different target persons in 13 different countries, was published last month by Duncan Watts, Ph.D. ’97, now a professor of sociology at Columbia University. During his time at Cornell, Watts was Strogatz’s student.

According to Strogatz, sync is a natural subset of complexity theory which itself was a byproduct of chaos theory. “To a scientist, chaos means complicated behavior in a system with few variables. There was a great explosion of our understanding of this in the 1980s and since then scientists have moved on to systems with lots of variables,” Strogatz said. This new arena is the realm of complexity theory.

Sync takes up the challenge of popularizing these emerging subjects with the general public — an endeavor previously pursued in books like James Gleick’s Chaos and Malcolm Gladwell’s The Tipping Point. However, like a good deal of the popular literature on these subjects, these texts were written by journalists.

According to Strogatz, much of the literature written by scientists in these fields is not readily accessible to the public.

“Most science writers either don’t know enough about science or enough about writing to be able to express the real reason why it’s interesting. So instead they fall back either on telling lots of anecdotes or pretending that the science is going to solve all the world’s problems. Steve doesn’t need to do that,” Watts said.

Since its publication in April, Sync has won acclaim from both the scientific community and the popular press with write-ups in Newsweek, The Washington Post, New Scientist and Popular Science, among others.

In addition to existing technologies that rely on synchronization, Strogatz says that sync holds the potential to reveal further useful applications.

“In addition to the shear wonder of knowing why crickets chirp in sync or how the cells in your heart keep in step for three billion beats in a lifetime, there are applications in medicine and communications. For example, maybe you want to understand cardiac arrhythmias or how the brain works. There are also applications in super conducting and wireless communications,” Strogatz said.

Strogatz is encouraged by the progress he sees in these new areas and the advances they are spurring in a whole range of fields. One of the limitations of sync and complexity, however, is that they do not yet possess the rigidity of the “harder” sciences.

“College physics, for example, has been around for a few hundred years so it’s fairly well understood. However, we are now living through the birth of a subject that is bigger than physics because it includes physics. I’m sure that the answers are coming, but it probably won’t be tomorrow,” Strogatz said.

If he is right, the quiet revolution that began in the
jungles of Southeast Asia is only beginning as scientists like Strogatz continue to explore the birth of order in a chaotic universe. Theirs is a search for mosaic from madness and symphony from sound, and Sync extends an invitation to the rest of us to join in.

Archived article by Philip Lane