Since the 1960s, the unit of time known as the "second," has been defined as 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 cesium 133 atom.
Today; however, increasing accuracy in types of atomic clocks may make that definition of time obsolete. Advancements in so-called optical atomic clocks could be used to more precisely define what exactly a second is. Scientists with the Boulder Atomic Clock Optical Network, or BACON, have been measuring the ratios between three of these new atomic clocks, reaching uncertainties less than one quadrillionth of a percent, or (1e(-17)).
This ability to compare distant optical atomic clocks to one another paves the way for greater precision measurements such as characterizing Earth's gravity and testing for fundamental physics.
From Science News, 24 Mar 2021
