Fabry and Perot's interferometer
The device that changed how we look at light – and our universe
When I had my house renovated a few years ago, our builder noticed something in the skylight. Smack in the centre of the triple-glazed pane was a set of gorgeous multicoloured rings. ‘Newton’s rings’, I said, as I made them expand and contract by pressing my fingers against the pane. ‘Aren’t they beautiful?’ He looked distinctly unimpressed; to him it was just a flaw.
Like the iridescent colours that appear in a pool of greasy water, films and gaps between transparent materials give rise to delicate colours. Sadly, Newton’s own thoughts on the origin of the coloured fringes were quite vague. It was not until the 1830s that the English astronomer George Biddell Airy, one of the great proponents of the wave theory of light, laid down the rigorous theory to describe the path of light passing between two parallel plates separated by a narrow gap, predicting that there would be interference. Airy’s formula would form the basis of an exceptionally sensitive interferometer that has been in use for well over a century. It was developed by a man who was obsessed with astronomy as a boy.