If you were in a spacecraft passing over the Earth's South Pole, you are likely to see a "polar vortex" — a huge swirling mass of clouds and winds in the upper atmosphere right above the pole, driven by the Earth’s rotation. The centre of the vortex is usually circular, but occasionally it assumes a triangular or even a square shape. Now researchers in Canada claim to have replicated this behaviour for the first time in the laboratory — using nothing more than water in a cylindrical bucket with a rotating base.

While it might seem strange that a circular vortex will suddenly develop corners, this curious behaviour was first hinted at over a century ago by the British physicist J J Thomson. Working on the now long-abandoned theory of “vortex atoms”, which assumed that each atom is a vortex in the ether, Thomson calculated that when a single vortex reaches a critical angular velocity, it will split into two vortices that orbit each other, making a diatomic molecule................