A 'Jiffy' is a Real Unit of Time

While we casually use the word "jiffy" to describe a very brief moment, its informal use dates back to at least the late 18th century, possibly originating as slang for lightning or from older words meaning a quick glimpse. However, this seemingly playful term holds a precise, scientific definition in the realm of physics, illustrating how even everyday language can find a rigorous application in scientific measurement.

In physics, the "jiffy" was first formally defined in 1926 by the physical chemist Gilbert Newton Lewis. He proposed it as the exact time it takes for light to travel one centimeter in a vacuum. This incredibly short duration is approximately 33.3 picoseconds. To put that into perspective, a picosecond itself is a trillionth of a second (10^-12 seconds), meaning light travels only about 0.30 millimeters in one picosecond.

The concept of a "jiffy" highlights the need for specialized units when dealing with phenomena at extreme speeds or scales. While Lewis's definition is prominent, the term has actually been adopted and redefined in various scientific fields to suit different contexts, all referring to extremely short intervals. For instance, in electronics, a "jiffy" can refer to the period of an alternating current power cycle, which is about 1/50 or 1/60 of a second. In computing, it historically represented the time between system timer interrupts, a duration that varies by hardware but is typically in milliseconds. This flexibility underscores the "jiffy's" utility as a convenient, albeit context-dependent, label for truly fleeting moments in time (Review).