Determinism in pop culture: Episode 2
In the 2004 movie The Butterfly Effect, Ashton Kutcher’s character tries to fix present-day problems by time-traveling back to his childhood and changing the past. As the movie’s title suggests, he gets more than he bargained for. Each time he tinkers with the past to improve one thing about the present, he makes something else worse. I count this movie as a portrayal of determinism because the butterfly effect applies only to deterministic systems.
I won’t complain here about the usual problems with Hollywood depictions of backward time-travel. Instead, I’ll complain that the movie makes not too much of the butterfly effect but too little. Kutcher’s character, Evan, travels back in time to stop a pedophile from abusing Evan’s childhood friend Kayleigh. He returns to the present only to find that the pedophile abused Kayleigh’s brother instead. Yet removing Kayleigh’s abuse from reality implies changes to the remote past that, almost certainly, preclude the existence of humans in the first place. But leave that aside. The movie underestimates the difference that changing even the recent past makes to the future.
The critic Roger Ebert glimpsed this problem, remarking that the movie’s changes are too “precisely aimed: They apparently affect only the [main] characters…. Do their lives have no effect on the wider world? Apparently not.” I say that Ebert only glimpsed the problem because, given the sensitivity of deterministic systems to even the slightest changes, the trajectories of the main characters themselves should diverge from actuality more drastically than the movie depicts.
Ebert writes that “a butterfly flapping its wings…could result in a hurricane halfway around the world. Yes, although given the number of butterflies and the determination with which they flap their little wings, isn’t it extraordinary how rarely that happens?” That passage contains a misunderstanding. Chaos theory does not predict that the number of hurricanes will be correlated with the number of times butterflies flap their wings. Rather, it says that a huge difference in the future behavior of a system can depend on the slightest difference now. Rewind a calm weather system far enough back, add (or remove) only the flap of a butterfly’s wings, and you can eventually get a hurricane instead.
