Scientists Are Preparing to Redefine the Second

The humble second—that little tick that occurs 86,400 times per day—is on the verge of being redefined for the first time in over half a century. In no way will this alter the length of workdays, happy hours, or anything else that motivates folks to keep an eye on the clock, but it means a lot to metrologists and other scientists. Indeed, the new definition could bring humanity a big step closer to detecting dark matter, gravitational waves, and other holy grails of fundamental physics. According to New York Times science reporter Alanna Mitchell, the “new, improved second” is coming thanks to a new type of instrument: the optical atomic clock. However, the process of redefining the second will take years; scientists with the International Bureau of Weights and Measurements hope to finalize it by 2030.

Through most of history, humans measured time based on observations of Earth’s movement relative to heavenly bodies, i.e., astronomical time. But Earth's rotation is not constant; it’s gradually slowing down by about one second every 18 months. This became problematic due to technological advances in the 20th century that demanded total precision, so scientists figured out how to measure atomic time, which is constant. Since 1967, the so-called cesium clock has set the international standard, but it's still not perfect. The new optical atomic clocks will deliver an unprecedented level of precision, eventually. Read the full story. (More atomic clock stories.)