I was reminded this week about the story of Huygens’ clocks. Christaan Huygens was one of those too-clever-by-half physicists / mathematicians who was into just about any science that was going on at the time. This seventeenth century dutchman is maybe best known in physics for his work on wave motion, but he was also an accomplished astronomer and clockmaker.
The story goes that Huygens had lots of clocks on his wall (as you might expect from a clockmaker), and although they were all slightly different, and were wound up at different times, they all eventually ticked together. By that I mean the tick-tock motion of every clock became exactly synchronised with every other clock.
Huygens realised the clocks were, in a sense, communicating with each other through vibrations in the wall, and that brought all the ticking into synchrony. This phenomenon is now known as a collective oscillation – and can occur whenever two or more oscillators (something that cycles backwards and forwards in some manner) with nearly similar cycle-length are brought together. Physicists commonly associate it with vibration of atoms in molecules and solids, but it can be much wider than that. Knowing, for example, how a building will vibrate in an earthquake is rather important.