Physics, Earth & Space Icon Physics, Earth & Space

The Butterfly Effect, Strange Attractors and Scientific Predictability

Monarch wing

Can the flapping of a butterfly’s wings really cause a tornado in Texas? The oft-quoted proverb from chaos theory would lead one to think nature is so unpredictable, anything can happen. If so, why do science?

Natalie Wolchover, writing for Live Science, investigated the provocative aphorism. The short answer to whether butterfly wings can cause tornadoes is, thankfully for Texans, no. A change in air pressure from a butterfly wing flap is so localized, it is quickly damped out. Empirical observation backs this up. There is no correlation to tornado count during the Monarch butterfly migration over Texas.

The idea behind the aphorism, of course, is not so simple; no one actually suggests a correlation between butterflies and tornadoes. Chaos theory posits that certain phenomena are so unpredictable that hair-trigger changes in initial conditions can cause wildly divergent outcomes. Weather is an example. Chaos theory limits the ability of meteorologists to make long-range forecasts. So goes the argument, slight changes in initial conditions can quickly grow into major differences in outcome, swamping our ability to predict the weather, the stock market, the path of a tornado, the severity of the hurricane season, and many other phenomena.

But is that true, or is it an excuse? With perfect knowledge of the initial conditions and forces at work, could weather forecasting achieve unlimited accuracy? The question becomes philosophically interesting. Victorian polymath Charles Babbage, father of the programmable calculator, believed the consensus of his day that the reliability of natural law makes phenomena infinitely predictable — a form of determinism. In his Ninth Bridgewater Treatise, chapter IX, he wrote that he considered it an absolute fact that every word uttered could be retrieved from the air, given sufficiently accurate observational tools. The laws of nature ensured it. Notice his ironic use of the phrase “strange chaos”:

Thus considered, what a strange chaos is this wide atmosphere we breathe! Every atom, impressed with good and with ill, retains at once the motions which philosophers and sages have imparted to it, mixed and combined in ten thousand ways with all that is worthless and base. The air itself is one vast library, on whose pages are forever written all that man has ever said or woman whispered. There, in their mutable but unerring characters, mixed with the earliest, as well as with the latest sighs of mortality, stand for ever recorded, vows unredeemed, promises unfulfilled, perpetuating in the united movements of each particle, the testimony of man’s changeful will.

Chaos theory was the second of two 20th-century scientific revolutions that undermined scientific determinism, the first being quantum mechanics. QM shattered the confidence that physicists felt in their ability to predict outcomes with infinite precision. Given our current understanding of the Uncertainty Principle, there is no way to tell which particular atom of an unstable isotope will decay, even though the half-life of a large number of atoms can be measured accurately. For all the philosophical worries it provokes, the Uncertainty Principle is generally regarded, in practical application, as applying only to extremely small-scale phenomena. Spacecraft navigators still employ Newton’s Laws to first order.

Chaos theory, on the other hand, does apply to macroscopic phenomena. The rotations of some asteroids and small bodies in the solar system, like Saturn’s moon Hyperion, are too chaotic to predict far into the future. Even so, there is an intrinsic order to chaotic systems. In the 1960s, Edward Lorenz discovered a “strange attractor” in his mathematical model. It showed that solutions to some interrelated equations, though chaotic, generated spirals around two centers of attraction that yielded a graph resembling a butterfly. Minute differences in initial conditions would produce a different graph, but the same general shape.

CREDIT: Creative Commons | Asturnut (butterfly), Creative Commons | Hellisp (attractors)

Wolchover interviewed David Orrell of Oxford, who has written a best-selling book about chaos theory and scientific prediction. Although he agrees that many systems defy prediction due to sensitivity to initial conditions, the “butterfly effect” is sometimes used as an excuse: “People started applying chaos theory to a lot of systems and saying, ‘Well, this property is sensitive to initial conditions, so we can’t make accurate predictions.'” Regarding butterflies, he added, “the changes that make a difference are far bigger than a butterfly flapping its wings.” Extreme sensitivity to initial conditions often comes out of simplistic models, he said; more sophisticated models, with more precise inputs, can constrain the outcomes. Scientists need not fear unpredictability, therefore. Weather forecasters could do better.
It’s an ongoing debate, as Wolchover explains. Other physicists are not so confident in the human ability to constrain chaos. Does chaos theory indicate a fundamental shortcoming in scientific predictability, or a mere limitation on current knowledge of nature that could be overcome with better tools and information?

We’ll leave that question to the philosophers of physics. One thing is predictable quite naturally; the “butterfly effect” on you will be profound when you watch the butterfly wings flapping in the new Illustra documentary, Metamorphosis: The Beauty and Design of Butterflies. This documentary is a not-so-strange attractor that will pull you into its orbit.
Thumbnail image for Thumbnail image for metamorphosis-bluray.jpgTo see how Monarch butterflies migrate past Texas tornadoes, and to witness other fascinating details of butterfly life cycles that defy Darwinian explanations, watch the trailer at, where you can order the film now at 10% off. If you’re finally upgrading that old DVD (or VHS!) player for the holidays, the stunning Blu-Ray version of Metamorphosis with 5.1 stereo would make a great addition to the gift box. It’s also available in standard DVD.

Consider ordering extra copies of this top-notch production as inexpensive gifts for family and friends — gifts with a message that will lift their minds and spirits with the beauty and power of intelligent design.