What is the butterfly effect?

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What is the butterfly effect?

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Answer 1

The butterfly effect is a story told to make the point that small changes can *sometimes* have large effects. The story is that if a butterfly flaps its wings in the Amazon rain forest, it can alter the course of a typhoon half a world away.

That’s an exaggeration, and is made worse when people further exaggerate the story and say a butterfly can start a typhoon all by itself. A more realistic example is that small changes in Earth’s orbit can and do cause big changes in Earth’s weather.

But it’s just as likely that small changes will have *no* discernible effect, and there’s no way of predicting which changes will matter. Sometimes, to paraphrase Ben Franklin, for want of a nail a kingdom is lost — but much more often the lack of a nail has a negligible effect on the kingdom, as one would expect.

The story of the butterfly effect was originally used by a meteorologist, Edward Lorenz (1917–2008). Lorenz used the story to make the point that it’s impossible to perfectly predict the weather because it’s impossible to know all the necessary variables. Weather is so complex that small variables can — sometimes — change the direction of a typhoon.

But Lorenz always stressed that there’s also no way of knowing *which* small variable results in a big change. Thus we can’t harness the power of butterflies to change the direction of typhoons and hurricanes. The butterfly was just an example of a small variable, but there are innumerable small variables and we can’t tell ahead of time which ones will matter.

The butterfly effect is also invoked in fictional time travel stories, where time travelers change the past in a small way and cause a large change when the return to the future. Time travel into the past is, of course, impossible. The stories also exaggerate the effect by making it seem certain that *any* small change will result in a wildly different future, whereas it’s more likely that the nearly all small changes won’t have a noticeable effect — although it is true that some might.