The official standard time of the United States is kept by around 10 to 15 atomic clocks at NIST laboratories in Boulder, Colorado. That’s clearly an important job, so the agency has backup generators in case the local grid fails due to, say, an unfortunate weather incident. But there wasn’t a backup generator for the backup generator when, last Wednesday, a powerful windstorm knocked out the power in Boulder.
The atomic clocks did have a battery backup system that kept them going for a while, but the “atomic ensemble time scale” failed due to a disconnect between some of the clocks and NIST’s measurement systems, according to a community email by NIST supervisory physicist Jeffrey Sherman on December 19.
“One impact is that the Boulder Internet Time Services no longer have an accurate time reference,” Sherman added. As a result, the U.S. official time slowed by around 4.8 microseconds—a timeframe that is “both big and small at the same time,” Sherman told NPR.
Timekeeping history
NIST, short for the National Institute of Standards and Technology, officially became America’s timekeeper in 2007 through the America COMPETES Act. As part of the Department of Commerce, NIST collaborates with the U.S. Navy to determine the precise time in the United States.
More informally, NIST and its predecessor, the National Bureau of Standards, had been managing the official time reference for industries like stock exchanges and the electric power sector since at least the 1960s.
Today, NIST’s standard time serves as a reference point for things like telecommunications and GPS signals. The atomic clock ensemble is a mix of hydrogen masers and cesium beam clocks, which produce a weighted average of physical signals that NIST researchers use to keep time.
Big but small, atomic time
The level of precision for atomic time is, quite literally, on the atomic scale. For context, the international standard for “1 second” corresponds to the “duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom,” according to NIST. What this means is that the slightest dissonance in the ensemble can cascade into serious errors.
To be fair, the 4.8 microsecond “drift” would be far too small for the general public to notice—the reason Sherman described the error as “both big and small.” To NPR, NIST clarified it had given “high-end” users access to other timekeeping networks to minimize disruptions from the Colorado power outage.
NIST staff was also able to address the issue in a reasonable amount of time. The power outage lasted around two hours, and critical operations staff on duty immediately activated a reserve diesel generator to keep the clocks running.
“Additional quick action by NIST facility staff secured temperature control for the most sensitive clocks,” Sherman added in a follow-up community message on Sunday. As of December 21, utility power had returned to NIST’s facilities, and “assessment and repair activity is in progress.”
Read the full article here
