Science Behind The Butterfly Effect

Forty-five years ago, Ed Lorenz changed one thing. And that changed everything.

Lorenz, a researcher at the Massachusetts Institute of Technology, neglected to program his computer one afternoon to calculate results of a weather simulation in five digits. He wanted to see a sequence again and, as a shortcut, set the machine to generate results rounded out to only three digits.

Although the adjustment was tiny, chaos stepped in and the computer produced completely different forecasts than it had before. Lorenz's discovery would come to rock the scientific world: Some systems are so complex, even making the smallest change can lead to practically unpredictable results — or chaos.

Now swap the computer's churning to a young man's life and the programming tweak to going back in time and altering the past and you've got a Hollywood movie.

The Butterfly Effect, a film from New Line Cinema, starring Ashton Kutcher, takes its inspiration from Lorenz's subsequent analogy, "Does the flap of a butterfly's wings in Brazil set off a tornado in Texas?" (Look for an adaptation of the quote at the start of the movie.)

But while Kutcher's movie character fails to grasp the concept of chaos as he repeatedly returns to the past to try and better his world, scientists are getting better at harnessing the power of chaos and Lorenz's so-called butterfly effect.

In fact, their work is leading to revelations in everything from weather prediction to managing alcoholism to gauging a marriage's success.

Using Chaos for the Weather Forecast

Bigger and better computers help when it comes to calculating chaos. Take, for example, Lorenz's field of weather prediction.

Weather is the result of some five million billion tons of air and water vapor churning around our planet. The interactions of so many moving parts are complex enough that, in some cases, even the proverbial flap of a butterfly's wing could possibly lead to a big weather change elsewhere.

To tackle that complexity, the National Weather Service now runs "ensemble forecasts," in which a computer model generates a model forecast and then several others that are each adjusted by slightly different factors. If the different forecasts end up being similar, meteorologists can forecast rain or snow or sun with high probability. If the forecasts don't agree, the probability rating drops.

The butterfly effect concept has also guided meteorologists to zero in on regions known as chaos hot spots to make weather predictions more accurate.

James Yorke, a math professor and chaos guru at the University of Maryland, recently led a team to identify these hot spots and showed these areas, which make up about 20 percent of the global map at one time, are more sensitive to small changes like the flapping of a butterfly wing.

By locating the perpetually shifting hot spots and taking good observations from them, meteorologists can get a step up on chaos and make better predictions.

Kerry Emanuel of the Massachusetts Institute of Technology in Cambridge, Mass., points out the finding sheds light on one caveat in Lorenz's butterfly theory.

"There are times and places where butterflies will make no difference," Emanuel said. "But in the right place and time, even a butterfly can alter the whole pattern of weather if you wait long enough."

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