The pendulum is a highly important system in physics. The oscillations carried out by a pendulum find relevance in many different fields. In reality we cannot merely consider isolated oscillations. Everything is linked, nothing stands for itself. The movement of a single pendulum can be described relatively easily. If one however considers the double pendulum, it seems to behave chaotically. An ultraviolet laser and a fluorescent foil cause an afterglow and make the pendulum’s history visible. The line which describes the pendulum’s movement is known as its trajectory. The theoretical calculation of this trajectory leads to coupled non-linear equations. This means that the solutions of the the two arms of the pendulum are inextricably linked. The nonlinearity of the equations means that a small change in the initial conditions causes a great change in the trajectory. If one lets the pendulum go twice consecutively, starting at almost the same position, a completely different pattern is obtained. If all parameters were controllable in reality, the chaos of the double pendulum could be controlled.