The
butterfly effect, used to describe many
chaotic phenomena, was first described as such in reference to
weather: that the beating of a
butterfly's wings in
Brazil might set off a
tornado in
Texas months later
1. Chaotic systems such as weather are said to be sensitively dependent on initial conditions, in that some small change may trigger a slightly larger change, which then triggers a slightly larger one, and so on, until it becomes completely impossible to predict long-range effects.
See Chaos theory.
1 Edward Lorenz, in a paper in 1963 given to the New York Academy of Sciences, said: "One meteorologist remarked that if the theory were correct, one flap of a seagull's wings would be enough to alter the course of the weather forever." Later speeches and papers by Lorenz used the more poetic butterfly.