The scientific notion referred to as the butterfly effect always comes with the same story: A butterfly flaps its wings in one place, and causes a hurricane halfway around the world. The story has become a kind of pop culture artifact, like a quasi-scientific urban legend.
But like so many urban legends, the truth of the matter is a bit elusive. Trace Dominguez breaks it down it today's DNews report.
First, some history: In 1961, MIT meteorology professor Edward Lorenz was inputting numbers to a computer program for simulating weather patterns. Running the numbers a second time, he rounded off figures from six decimal places to three decimal places, figuring there wouldn't be much change. To his great surprise, those few fractions of a fraction changed the simulation completely.
The incident led Lorenz to a profound mathematical insight on how large systems, like global weather patterns, actually work. The simulation suggested that tiny initial changes in big systems could have extremely complex results. His insight became a bedrock principle in the discipline of mathematics now known as chaos theory.
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In 1972, Lorenz presented a paper titled "Predictability: Does the Flap of a Butterfly's Wings in Brazil Set Off a Tornado in Texas?" The concept of the butterfly effect comes from the title of this presentation, but its meaning has been gradually altered in 50 years of retelling.
The point of the notional scenario is not that the Brazil butterfly caused the Texas Tornado. In fact, it's kind of the opposite: It's that the butterfly effect -- also known as "sensitive dependence on initial conditions" -- makes causality virtually impossible to determine in complex systems.
It gets weirder. The story of the butterfly effect has generated its own odd vortex of ambiguous causality. For instance, the origin of the phrase is often attributed Ray Bradbury's 1952 short story A Sound of Thunder, in which the death of a butterfly in the past has repercussions in the future. In fact, the phrase does not come from this story -- published 10 years before Lorenz's discovery -- and yet the story is a perfect illustration of the principle of the butterfly effect.
One more twist: If you plot out the values from Lorenz's mathematical system in two dimensions, it looks like a butterfly. Trippy. Check out Trace's report for many more details, some helpful visual aids and an excellent sustained metaphor concerning carnival rides.
-- Glenn McDonald
LiveScience: Can a Butterfly in Brazil Really Cause a Tornado in Texas?
Technology Review: When the Butterfly Effect Took Flight
University of Houston: The Butterfly Effect