before it's in the papers"
August 03, 2010
TO THE WORLD SCIENCE HOME PAGE
Order from chaos
Courtesy Washington University in St. Louis
and World Science staff
One of the most baffling, perhaps
deepest puzzles of nature is quite different from the grand questions physicists love to ponder—the fate of the universe, the nature of the invisible “dark energy” filling it, and the like.
The mystery has to do with a common class of events that can occur in full view. They’re wildly diverse, but they share one feature: chaos, inexplicably, leads to order.
|A violin can be envisioned as a system of
"coupled" oscillators, vibrating things (strings) that are
connected together so that each oscillator influences the motions of
neighboring ones. (Photo courtesy stock.xchng)
In a new study, physicists explored this mystery. They didn’t find an answer, they said, but at least helped clarify the problem.
The researchers worked on a computer simulation of a network of “pendulums.” They chose pendulums as representative of a wider class of objects known as oscillators.
An oscillator is anything that somehow swings back and forth rhythmically when disturbed. Under the right conditions almost any sorts of objects, including atoms, can be oscillators.
The “pendulums” in the simulation were loosely connected to each other, as oscillators also are in many natural situations. A classic example of such “coupled” oscillators is pendulums with springs linking their ends together. Other common cases are violin strings, which are connected by their sounding boards, and electrical filters used in communications.
The scientists found that the pendulums, when pushed by forces according to a regular rhythm, behaved chaotically and swung out of sync. Yet when the researchers introduced disorder—applying forces at random intervals to each oscillator—they began to swing in synch. The “forces” were applied along the rods of the “pendulums” to make them swing.
“When you introduce disorder… the chaos that was present before disappears and there is order,” said Sebastian F. Brandt, a physics graduate student at Washington University in St. Louis and lead author of the study. The findings appeared in the January issue of the research journal Physical Review Letters.
Physicists are as bewildered by all this as anyone else, said Ralf Wessel, a Washington University physicist who supervised the study: “Every physicist who hears this is surprised.”
Physicists have long studied the
relationship between order and disorder, sometimes pointing to the
emergence of life itself as an example of order arising from its
A more everyday example of chaos creating order might be that old favorite way of fixing a broken TV set—hitting it, Brandt said. Sometimes this solves the problem, but not always, he added, illustrating that the
surprising ability of chaos to produce order only goes so far. It in fact works only with certain systems, Brandt added.
“It is much more common that disordered processes destroy spatial and temporal regularity,” he wrote in an email.
Research on the role of disorder in “complex” systems such as coupled oscillators is quite new and poorly understood, the researchers said, but they believe their model could shed light on real-life processes.
Brain cells, for example, have been studied as coupled oscillators because of the way they interact. They sometimes appear to display repetitive electrical activity affected by neighboring cells’ activity.
Though it’s a bit of a stretch, the study may help to solve previously unexplained findings, said Babette Dellen, a member of the research team. Brain cells, she explained, can act in synch in response to a stimulus, but no one knows why. “Maybe the details of neurons [cells] are completely irrelevant,” Wessel remarked. “Maybe it is only a property of oscillators.”
A key similarity between the simulated system and neurons is that they are both “nonlinear,” meaning the applied force has no straightforward relationship to the distance moved, the researchers said.
A linear system is like a child being pushed gently on a swing. He’ll move in proportion to how hard you push: push twice as hard, and he’ll go twice as far. But past a certain height, pushing twice as hard won’t double the distance. The system is now nonlinear.
Nearly all complex systems in nature are nonlinear, like the physicists’ model, they explained. So are neurons, which is why “when you hear your favorite music twice as loud you don’t double the pleasure,” Brandt said.
Previous research had also shown that disorder can create order. But past studies often involved manipulating properties of the system itself, such as changing pendulum length, Brandt added.
What’s new in this study, he said, is that it involves changing externally applied forces. Thus, he argued, the findings might be applicable to the real world, where it would be harder to change parameters within the system—neurons, for example—but not so hard to apply external forces. “It will be interesting to see if the mechanism that we have found can actually be put to some use,” Brandt said.
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