Ytterbium clocks set records for accuracy and could find dark matter

Just how accurate is your clock? The one on your microwave or in your car might be up to an hour off depending on how diligently you update it. The new atomic clocks at the National Institute of Standards and Technology (NIST) in the U.S. would lose just half a second if they lasted 14 billion years.

That’s pretty good, but that’s hardly all the ytterbium clocks can do. They can measure the size and shape of the Earth, detect gravitational waves, test general relativity, even search for dark matter and the origins of the universe.

To measure time, the twin clocks capture 1,000 atoms of ytterbium in laser beam grids. They “tick” about 500 trillion times every second, with a margin of error of approximately one billionth of a billionth of a vibration of those atoms. The two clocks are almost in perfect synchronicity, again less than a billionth of a billionth of a vibration apart.

“Systematic uncertainty, stability, and reproducibility can be considered the ‘royal flush’ of performance for these clocks,” project leader Andrew Ludlow said. “The agreement of the two clocks at this unprecedented level, which we call reproducibility, is perhaps the single most important result, because it essentially requires and substantiates the other two results.

“This is especially true because the demonstrated reproducibility shows that the clocks’ total error drops below our general ability to account for gravity’s effect on time here on Earth. Hence, as we envision clocks like these being used around the country or world, their relative performance would be, for the first time, limited by Earth’s gravitational effects.”

According to Einstein’s theory of relativity, time passes more slowly in stronger gravity. In other words, time is slower at sea level than on top of a mountain or in space, where things farther from Earth’s center of gravity. This is usually a problem for accurate timekeeping, but by measuring the difference in the frequency of atomic vibrations at different spots, the ytterbium clocks could detect subtle changes in gravity, providing an exceedingly accurate topographical map.

Dark matter might make up as much as 80 per cent of the universe’s mass and a quarter of its energy density — yet since it doesn’t reflect, absorb, or give off light or any other form of observable electromagnetic radiation, it’s extremely difficult to detect. By detecting subtle distortions in space-time, the ytterbium clocks might be able to pick up the presence of dark matter.

“The ytterbium atom is among potential candidates for the future redefinition of the second” in terms of optical frequencies, the NIST said. Yes, in addition to everything else, a ytterbium clock might actually change how we measure time.