A Jiffy Is a Real Unit of Time

Wait a jiffy sounds like the vaguest possible instruction, the verbal equivalent of a shrug. In several serious fields it is nothing of the sort. It is a defined quantity, and if you ask three specialists how long one lasts you will get three answers, all of them precise and none of them the same.

In electronics a jiffy is one cycle of the mains supply — a sixtieth of a second where the grid runs at 60 Hz, a fiftieth where it runs at 50. Early computers borrowed the idea and counted time in ticks of their own, so a jiffy in an operating system is however long that machine has decided to make it, typically a hundredth of a second.

Physics is where it gets silly. There a jiffy was proposed as the time light takes to cross a distance about the width of an atomic nucleus, which works out at roughly a septillionth of a second. If somebody tells you they will be with you in a jiffy and they happen to be a particle physicist, you have grounds to be alarmed.

The pleasing part is the direction the word travelled. It began as slang, casual and unmeasured, and ended up carrying a number — the reverse of the usual journey, in which a precise thing gets loosened by everyday use until it means almost nothing at all.