Why We Call It the "Butterfly Effect"—and What You Might Be Getting Wrong

If a butterfly flaps its wings in Brazil, can it start a tornado in Texas?

This was the title of a talk by meteorologist Edward Lorenz given at the American Association for the Advancement of Science in 1972. The talk explored a phenomenon that Lorenz had been studying since the early 1960s, and gave it a name: the “butterfly effect.” 

Lorenz’s answer to the above question was, in short, that we can’t know. A butterfly’s wings could start a tornado, but they could also prevent one—and there’s really no way to know if it actually will. 

The origins of the butterfly effect and the rise of chaos theory

Lorenz first conceptualized what would become known as the “butterfly effect” while a professor at the Massachusetts Institute of Technology, where he was using computer models to simulate weather patterns. When he rounded a value in a simulation from 0.506127 to 0.506, the result diverged dramatically from what it had been before. 

This turn of events inspired Lorenz to propose that tiny changes can lead to dramatically different outcomes within systems, an idea he developed further in his 1963 paper “Deterministic Nonperiodic Flow.” (He used a seagull’s wings in his example there, and later brought in the butterfly, in part inspired by a data visualization that resembled a butterfly's wings.) The concept helped lay the foundation for chaos theory, a branch of mathematics that examines how seemingly simple, deterministic systems can exhibit highly unpredictable behavior due to their extreme sensitivity to initial conditions. 

Lorenz’s research helped challenge the prevailing scientific belief that similar starting conditions should produce similar outcomes in certain systems. It also demonstrated significant limits on long-range weather prediction. Ultimately, it indicated that predicting the long-term behavior of certain complex systems is difficult, given just how sensitive these systems are to even the tiniest alterations.

“The 'innumerable' interconnections of nature, Lorenz noted, mean a butterfly's flap could cause a tornado—or, for all we know, could prevent one,” Peter Dizikes explains in the Boston Globe. “Similarly, should we make even a tiny alteration to nature, 'we shall never know what would have happened if we had not disturbed it,' since subsequent changes are too complex and entangled to restore a previous state.”

Mentions of similar concepts to the butterfly effect predate Lorenz’s research. In his 1952 short story “A Sound of Thunder,” the ever-prescient Ray Bradbury wrote of a man who goes back in time to hunt dinosaurs but returns to the future to find that everything is different. He then finds a dead butterfly on his boot, and realizes he stepped on it in the past. 

Misconceptions about the butterfly effect

Over the years, the butterfly effect has become a popular term. Yet, more often than not, it is used imprecisely. 

For example, people often retroactively trace big events in their lives back to small choices and call this the butterfly effect. Someone might say (or more likely post on social media), “The butterfly effect is crazy! If I hadn’t been to that party, I never would have met my husband.” This, however, isn’t quite the correct way to use this term. The butterfly effect describes the idea that small changes in systems can have any number of unpredictable effects, not that big events can be directly traced back to small changes.

Another misuse of the term appears in the 1990 film Havana, in a scene where Robert Redford’s character says, “A butterfly can flutter its wings over a flower in China and cause a hurricane in the Caribbean.” This makes it seem like a butterfly’s fluttering wings can cause hurricanes. However, the actual butterfly effect holds that it is generally not possible to predict the outcomes of small changes, like the fluttering of a butterfly’s wings, or to retroactively connect them to something like a hurricane.

There is certainly something poetic about believing that the butterfly effect led you to the love of your life. Technically, though, the butterfly effect merely expresses the fact that going to a party (or not going) could (or could not) vastly change your life in unknowable ways—and in the end, there’s no way to know.

“Pop culture references to the butterfly effect may be bad physics, but they're a good barometer of how the public thinks about science,” Dizikes notes. “They expose the growing chasm between what the public expects from scientific research—that is, a series of ever more precise answers about the world we live in—and the realms of uncertainty into which modern science is taking us.”

Ultimately, the butterfly effect does serve as a reminder of just how much of a difference tiny changes and small choices can make. It just also includes the caveat that we can’t predict the storms that our little ripples might, or might not, conjure up in distant lands or our own lives.