A Sound of Thunder and The Butterfly Effect

In the late 80’s, I watched many episodes of The Ray Bradbury Theater – a television series adaptation of the works of the science fiction writer, Ray Bradbury. For a few years, my friends and I gathered on Friday nights to watch it live; there was no binge-watching in those days and no one ever thought of recording the show on a VCR. The series had a strong effect on me by expanding my thinking; many famous people apparently had a similar reaction.

One episode stood out to me, even to this day: A Sound of Thunder. While the TV episode aired in 1989, Bradbury wrote the short story in 1952. Here’s a summary:

Set in 2055, it tells of a man named Eckels who travels back 65 million years to shoot a dinosaur. Warned not to deviate from the tour guide’s plan, Eckels along with a guide heads off to kill a T Rex who was going to die soon anyway when a falling tree lands on it. Eckels panics at the sight of the creature and steps off the path, leaving his guide to kill the T Rex. Upon arrival back in 2055, they are confused to find that the world has changed. Language is altered and an evil dictator is now in charge. A confused Eckels notices a crushed butterfly stuck to his boot and realizes that in stepping off the path, he killed the insect and changed the future.

Like many science fiction writers, Bradbury is trying to do more than just entertain us. He’s asking fundamental questions about the nature of time and whether events are deterministic or not.

Eckels’ mind whirled. It couldn’t change things. Killing one butterfly couldn’t be that important! Could it?

This is a subject many books and movies have explored since.

Until recently, I assumed that this short story was the origin of the butterfly effect. In case you’re not familiar with the concept, the butterfly effect suggests the path and force of a tornado this week could be influenced by minor perturbations in the past, such as the flapping of a butterfly’s wings.

In fact, the concept is typically credited to the meteorologist Edward Lorenz who rejected the existing linear models to forecast weather and essentially created chaos theory. Lorenz found that very small changes to the initial conditions of weather models produced significantly different predictions. Since it is impractical to know the precise starting conditions for any weather model, he showed that existing predictions were inaccurate. For those interested in the math, you can read his award-winning paper Deterministic Nonperiodic Flow.

As chaos theory was not intuitive to the general population, Lorenz began to use the butterfly analogy to explain his findings. I cannot find any evidence of it but it is intriguing to speculate that Bradbury’s short story might have inspired Lorenz. After all, Lorenz’s research was conducted in the mid-1950’s, only a few years after A Sound of Thunder was published.

One footnote to all of this. While the butterfly effect has successfully entered popular culture, I find that people misunderstand its meaning. Lorenz uses the metaphor to explain there is an inherit limit to predictive accuracy but many people use it to rationalize why major events can be explained by seemingly inconsequential reasons. As I’ve previously written, this is because humans gravitate towards order and explanations of the unknown. We are constantly searching for causes, even if they don’t exist.

And yes, seeing a single butterfly was the inspiration for this post.