What Is This?

This ragged cloud of colour looks messy and unstructured -- but in fact it's a rare and unusual view of one of the most fundamental things in science. Can you work out what it is?

To stop you going round in circles, here are a couple of clues: it was generated by a computer, and the thing it depicts is used in every branch of science, from mathematics to engineering.

It is in fact none other than that famous mathematical constant Pi. The image is a "walk" made out of the first 100 billion digits of pi, in base 4.

Starting at the origin, each digit forced a point to move in one of four directions: a 0 made the point move right, a 1 made the point move up, a 2 left and 3 down. What you see is the route that 100 billion digits traced out. The result is beautiful, if chaotic. [Gigapan via Flowing Data]