A drop of water bounces off a soap film

Image by John Bush & Tristan Gilet

by Anne Trafton in Physics / Physics

MIT math professor John Bush and visiting student Tristan Gilet built the system in the Applied Math Laboratory, then demonstrated that the drop bouncing may be accurately described with a single simple equation. They report their findings in an upcoming issue of *Physical Review Letters.*

Their study builds upon the pioneering work of the late Edward Lorenz, an MIT meteorologist who in 1963 discovered chaos in a simplified mathematical model of the atmosphere, now called the Lorenz equations. Known as the father of chaos theory, Lorenz passed away in April 2008 after a distinguished career in MIT's Department of Earth, Atmosphere and Planetary Sciences.

The trademark of chaotic systems is their sensitivity to initial conditions. Any uncertainty in the initial state of a chaotic system will soon be amplified, leading to a loss of predictive power over the system. The chaotic nature of the Earth's atmosphere is responsible for the shortcomings of weather forecasts, which are notoriously untrustworthy beyond a few days.

Since Lorenz's early work, chaos has been discovered in a wide variety of complex systems, from the beating heart to population dynamics, from planetary orbits to the stock market. An interesting philosophical question arises, says Bush: "What is the simplest physical system that exhibits chaotic behavior? What are the minimum ingredients for chaos?"

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