But they didn’t. The aether therefore did not exist. And that observational pebble, gathering speed as it rolled downhill, produced an avalanche which swept away classical physics and cleared the field for Albert Einstein’s theories of relativity—one of which, the general theory, encapsulates the modern description of gravity.

It is therefore poetic justice that the latest attempt to sweep away Einstein’s version of the world in its turn also relies on an interferometer. This time, though, the beams travelling through it are made not of light, but of atoms.