"The Sound of Thunder"
In "The Sound of Thunder," a boorish big-game hunter travels back in time to shoot a Tyrannosaurus rex. The Tyrannosaur is already fated to die naturally just minutes before the hunter's arrival, allowing him to kill the dinosaur without affecting the future. But the hunter panics, disobeys instructions and with one tiny action sets off a cascade of unintended consequences. Returning to their own time, the hunting party finds a very different world.
"It fell to the floor, an exquisite thing, a small thing that could upset balances and knock down a line of small dominoes and then big dominoes and then gigantic dominoes, all down the years across Time," Bradbury wrote. "Eckels' mind whirled. It couldn't change things. Killing one butterfly couldn't be that important! Could it?"
In 1961, a decade after the story's publication, mathematician Edward Lorenz articulated the "butterfly effect," a piece of chaos theory describing how small changes to complex systems really might alter history's course.
Whether a butterfly's death would actually do so is, of course, untestable. Perhaps it would simply give another butterfly a chance to survive, and the two would cancel each other out. One thing is known, though: The Tyrannosaur's flesh would not have glittered "like a thousand green coins," as it would have been covered in proto-feathers.
Image: Artist's impression of Yutyrannus huali, a relative of Tyrannosaurus rex. Image: Brian Choo