Last night, BBC 4 showed The Secret Life of Chaos, one of the best science documentaries I’ve seen for a long time. In it, they showed the BZ reaction, a chemical reaction resulting in travelling bands of colour- a pattern arising from disorder. I’ve included a brief explanation below, but frankly, this is just cool.
This is a type of autocatalytic reaction. The reaction starts at random points in the chemical mixture, but there is a kind of feedback so that this triggers more reactions at the same place. This spreads out in all directions so you end up with a circular wavefront.
Usually, chemical reactions take place in one direction- A and B react to make C. However, in some special cases, the reaction can oscillate between two states. This can be seen as a mixture changing colour, then changing back in a repeated cycle. So, after one wave has passed through the mixture, other waves follow as the reaction oscillates between two states.
This is an example of self-organisation, a process whereby patterns emerge from disordered systems. It happens everywhere, from the nano scale to the formation of the universe. If you’re really interested, read Philip Ball’s recent Nature’s Patterns series of books (OUP).