Butterfly Effect
Etymology
The phrase comes from meteorologist Edward Lorenz, a founder of chaos theory, and the title of his 1972 talk asking whether the flap of a butterfly’s wings in Brazil could set off a tornado in Texas. It captures how minute perturbations get magnified through a system’s dynamics. The image has since escaped the science into everyday speech.
noun phrase · /BUT-er-fly ih-FEKT/
The way tiny differences in a system’s starting conditions can amplify into vastly different outcomes.
What it names
A vivid handle for sensitive dependence — why long-range forecasts of weather, markets, or history are inherently limited, since immeasurably small causes can swamp large ones over time.
Example
A missed train, a chance conversation on the platform — the butterfly effect of that morning rerouted her whole career.
Related idea
It is the engine inside chaos: the butterfly effect names the mechanism (sensitive dependence on initial conditions), while chaos names the overall regime in which that mechanism reigns.