And it could happen as soon as 2030.
A second is only a second because we’ve defined it as such. And that definition has changed over, well, time. In fact, it may change again later this decade.
The International Bureau of Weights and Measures, located just outside of Paris and known by its French acronym BIPM, governs the second, according to The New York Times. Currently, the group is scrutinizing the definition of the second, a key time measurement that has ramifications across most of the seven base units of measurement that the BIPM monitors. Those include time, length, mass, electrical current, temperature, light intensity, and the amount of a substance.
This potential reconfiguring of the second boils down to advancements in clocks— specifically, their ability to track atomic wavelengths.
For centuries, our world measured time based on Earth’s spin. From ancient Egyptians to Greek astronomers and Babylonians, we’ve steadily refined the measurement of time into days, hours, minutes, and seconds. But as Earth’s rotation slows and changes, our ability to track time has become less accurate; at one time, we lost more than three hours over the span of just 2,000 years. The irregularity of Earth’s spin led scientists to study a new way to measure time. Cue the atom.
In 1967, after decades of study, we tossed out the Earth-spin method and redefined time by instead measuring the particle movements inside an atom. Specifically, we’ve landed on the natural frequency resonance of cesium 133. Now, officially, “the second is defined by taking the fixed numerical value of the cesium frequency.”
Decades ago, we liked cesium 133 since it is liquid metal, making it easy to track. A heavy atom with slow particle movement led to a steady and easily traceable wavelength. And it turned out to be more reliable than the ticking of a clock. Don’t fret, we still appreciate Earth and its path, but we now make astronomical time catch up to the more accurate atomic time, adding leap seconds when needed—two of them were added in 1972, and we add another one about every 18 months.
But improving upon the cesium 133 atom comes with improvements in our laser capabilities. There are a couple dozen high-level optic atomic clocks scattered around the globe—including three in Boulder, Colorado. By measuring multiple atoms and probing them for their wavelengths, scientists the world over remain in a continual state of research to find a more accurate atom to more precisely define a second, the unit of time that binds much of the world’s measurements together.
Femtosecond-laser frequency comb lasers—think: directly counting optical cycles with femtosecond resolution—can now measure atoms moving more quickly than cesium, and that has offered new areas of study for researchers still in awe of how Albert Einstein’s theory of general relativity likely plays out. He said that time moves more slowly when closer to a major planet, as gravity’s pull is different. It turns out this could be true down to the centimeter.
In Boulder, for example, three different optical atomic clocks spread across different laboratories were getting slightly different readings, and experts from the National Institute of Standards and Technology, the American contributors to the BIPM, believe it had to do with the clock’s height relative to sea level. The higher the clock, the faster it ran.
With advancements in lasers tracking the movement inside atoms, researchers will continue to probe atom wavelengths for their reliability of movement. The global body BIPM, working to define a second, may prove ready to entertain discussion of a new definition later this decade with potential approval occurring by 2030.
It may not seem worth the time for the less atom-enthused observers, but scientists say that a more accurate rendering of a second could open research into dark matter and shifts in gravitational waves—things definitely worth spending a second on.