Is a 'Jiffy' Really a Unit of Time? The Science Explained

You've probably said "I'll be back in a jiffy" without realizing you were referencing actual science. Turns out, a jiffy is a legitimate unit of time used by physicists and engineers—though its definition might surprise you.

Here's the twist: there's no single answer to "how long is a jiffy?" Depending on who's measuring and why, a jiffy can range from a split-second to an almost incomprehensibly tiny fraction of time.

The Physics Jiffy: Absurdly Fast

In physics, a jiffy was first defined in 1926 by chemist Gilbert Newton Lewis. His version? The time it takes light to travel one centimeter in a vacuum. That works out to about 33.3 picoseconds—or 0.0000000000333 seconds if you want to see all those zeros.

To put that in perspective, a picosecond is to one second what one second is to about 31,700 years. Light is ridiculously fast, and a centimeter is short, so a physics jiffy is absurdly brief.

Some physicists use an even shorter jiffy: the time light takes to cross a fermi (the approximate width of a proton). That's about 3 × 10^-24 seconds. At that scale, we're measuring events happening inside atomic nuclei.

The Electrical Engineering Jiffy: Actually Noticeable

If you're an electrical engineer, your jiffy is much longer and actually relates to that "1/100th of a second" claim. In this context, a jiffy is the period of one alternating current cycle.

• In North America (60 Hz power): 1/60th of a second (about 16.7 milliseconds)
• In Europe and most of the world (50 Hz power): 1/50th of a second (20 milliseconds)

This is the jiffy your microwave or computer power supply might care about. It's still quick—your eye can't perceive individual jiffies—but it's 600 billion times longer than the physics version.

The Computing Jiffy: It Depends

In early computing, a jiffy referred to the interval between system timer interrupts—basically how often the computer's internal clock ticked. This varied by system but was often tied to the AC power frequency, so again, 1/60th or 1/50th of a second.

Modern operating systems still use "jiffy" internally, though the exact duration depends on the system configuration. Linux, for example, typically uses 1/100th or 1/1000th of a second.

So What's the Right Answer?

They all are! Language is funny that way. "Jiffy" started as casual slang for "a short time," then got adopted by different scientific fields for their specific needs. A physicist timing particle interactions and an electrician analyzing power grids need very different levels of precision.

The next time someone says they'll be ready "in a jiffy," you can ask whether they mean a quantum physics jiffy or an electrical engineering jiffy. They'll either laugh or back away slowly. Either way, you've made the conversation more interesting.