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ILLUMINATION

# Why I Don’t Believe in the Butterfly Effect, Part 1

Part 1 of 12: An Introduction

The butterfly effect refers to the phenomenon in which a system is so chaotic that if you induce even a negligibly small change, it is enough to yield wildly different results after some time. It is the central concept of chaos theory, a theory that encompasses math, science, and various other disciplines.

Chaos theory and the butterfly effect were proposed by the meteorologist Edward Lorenz in the early 1960s. (Some aspects of the idea had been proposed earlier, but Lorenz was the first person to explicitly and vocally promote the theory.) He came to his discovery because he was running computer models to predict the weather. These models — like most weather models — consisted of a set of differential equations in which you plug in the initial conditions (temperature, pressure, etc.), and the computer uses the equations to calculate the values of the variables (temperature, precipitation, etc.) at each successive time step. Lorenz first ran the model with many digits included in the initial conditions. He then rounded off the initial conditions — only a very slight modification — and then ran the model again. He found that the new results diverged from the previous results after a few weeks’ time, such that the rounded initial conditions yielded completely different predictions about what would happen two months later than the more precise initial conditions did. And that’s the butterfly effect: if you make even the smallest change to the initial conditions — like adding a butterfly flapping its wings — then after some time, the results will be wildly different. And so, as they say, a butterfly flapping its wings in Brazil makes a tornado in Texas.

But in our popular understanding, the butterfly effect is not just a phenomenon in atmospheric science. Both before and after Lorenz, people have been applying that same line of reasoning to many other fields: history, sports, science fiction, our own life stories, etc. My next essay, Part 2, will detail some of these applications. That is, I will list some of the ways in which the idea of the butterfly effect shows up in pop culture.

Other parts of this series:

Part 2: The Butterfly Effect in Pop Culture

Part 3: The Wrong Way to Disprove It

Part 4: My Central Argument

Part 5: Responding to Arguments in Favor of the Butterfly Effect

Part 6: Exceptions (And Why They Aren’t Really Exceptions)

Part 7: Three Wrong Ways to Discuss Alternative History

Part 8: The Right Way to Discuss Alternative History

Part 9: How I Would Interpret Lorenz’s Observations

Part 10: The Butterfly Effect and the Slippery Slope

Part 12: Conclusion

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