Chaotic systems: head-on collison of two dipolar vortices in a stratified fluid environment. The original vortices, dyed orange and green, have exchanged a partner to form two new (mixed) dipoles which are moving at roughly right angles to the original direction of travel, that is, towards the top & bottom of the image. The green fluid was injected from the right, the orange from the left. Dipolar vortices are relevant to turbulence in large-scale geophysical systems such as the atmosphere or oceans. Turbulence in fluid systems is one example of a chaotic system.