Glossary of Astronomical Terms/chaos

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Chaos, in physics and astronomy, is a state of existence which, although evolving in time and governed by simple exact laws, is highly sensitive to starting conditions. In other words, if two systems that are initially equivalent except for seemingly insignificant, tiny variations, they can develop over time into wildly different resulting states. This implies that ideal models of systems which have this sensitivity to initial conditions are not reliable predictors of the system's future behavior. Earth's atmosphere is an example of a chaotic system, and computer models of it are examples of the limitations of such models.

A perhaps exaggerated but memorable statement about chaotic systems that will help you to remember what they are is: "If a butterfly in China flaps its wings, the weather in New York can be affected two weeks later."