You’ve probably heard people say things like “I’ll be there in a jiffy,” using “jiffy” to mean a very short period of time — something like the blink of an eye. But it may surprise you to learn that for some scientists, the term has a more precise definition. That definition varies depending on who’s doing the talking: The physical chemist Gilbert Newton Lewis (1875–1946) defined a jiffy as the length of time it takes for light to travel one centimeter in a vacuum. However, some physicists have defined a jiffy as the time it takes light to travel one femtometer — one millionth of a millionth of a millimeter. By this account, each second contains roughly three hundred thousand billion billion jiffys.
But a jiffy has also been defined outside of physics and chemistry. An electrical engineer, for example, might describe a jiffy as the time it takes for a single cycle of alternating current, which is 1/50 or 1/60 of a second depending on the electrical system. Whatever definition holds true, one thing is certain — no one in the history of the world has ever truly accomplished much “in a jiffy.”
It’s forgivable to think a second is 1/60 of a minute (or 1/86,400 of a day). After all, it’s pretty prominently displayed on every clock and watch ever built. But time isn’t nearly as neat as our timekeeping devices make it out to be. The universe is full of astronomical quirks, and for scientific purposes a second needs to be much more precise than a simple fraction. That’s why, in 1967, scientists changed the official definition of a second from 1/86,400 of a day to “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.” This is the basic principle behind atomic clocks, super-accurate instruments that use atomic physics to maintain long-lasting accuracy. For some state-of-the-art devices, it would take 15 billion years for the clock to be off by one second.