What is the butterfly effect?

Representative image.
| Photo Credit: Aarn Giri

You’re likely to have heard about the butterfly effect and just as likely to have heard the example of a butterfly flapping its wings in one place and causing a tornado thousands of kilometres away. The discovery of the effect has its origins in the work of the American mathematician Edward Lorenz, who pioneered the use of computers and mathematical models to predict the weather.

Before him, the mathematicians Henri Poincare and Norbert Wiener noticed that the earth’s atmosphere was never entirely stable and that the weather could be affected by very small changes, sometimes far away. Lorenz used computers to create mathematical models of this deterministic chaos and with them tried to predict the weather.

The butterfly effect is a statement about the property of this chaotic system: its final outcome is highly sensitive to its starting conditions. If one of these conditions changes just a little, the final outcome could be very different — like a hot, dry day rather than a bleak, damp one. Lorenz wrote that in one forecast model he was running in 1961, changing the value of some input variable from 0.506127 to 0.506 resulted in a drastically different prediction for the weather two months later.

Scientists have observed the butterfly effect in a variety of fields. A new branch of study called quantum chaos is in fact concerned with understanding ‘classical’ chaos using quantum theory.