It’s spring here in southern California the butterflies are starting their annual emergence. What effect will the butterflies have on the weather remains to be seen. The so called “butterfly effect” is an often used phrase used to refer to a property of nonlinear systems where a small change in initial conditions can have large effects later on. The name derives from the notion that a butterfly flapping its wings in Brazil might set off a tornado in Texas. Sometimes these conditions even create chaotic movements such as can be seen in this video of a double pendulum. Notice that if you don’t swing the double pendulum too far, it seems to act like a regular single pendulum.