US scientists debut atomic clock that stays true for 100 million years straight

Marvel's Time Variance Authority (TVA) would probably call dibs on this atomic clock if they could!
The NIST-F4 atomic clock, recently unveiled by the National Institute of Standards and Technology in Boulder, Colorado, is one of the most accurate timekeeping devices ever built on Earth.
This clock is so precise that if it had started ticking during the age of the dinosaurs, it would still be accurate today to within a single second.
This month, NIST scientists officially submitted it to the International Bureau of Weights and Measures (BIPM) for certification as a 'primary frequency standard,' a title reserved for the most elite atomic clocks on the planet.
Only around ten countries operate such clocks — now the U.S. is back in that top tier.
Unlike regular clocks, atomic clocks like NIST-F4 keep time using the natural vibrations of atoms — in this case, cesium atoms.
Inside the clock, thousands of these atoms are cooled to near absolute zero using lasers and then tossed upward in a fountain-like motion.
As they rise and fall, they pass through microwave radiation tuned to a frequency that makes the atoms shift their energy state — a transition that defines the "tick" of the clock.
That tick happens precisely 9,192,631,770 times per second, and counting those ticks is how the clock defines the official second.
"Fountain clocks are supposed to be very boring," said Greg Hoth, a physicist on the NIST team.
In this case, boring means reliable, and that's exactly what global systems depend on.
Time isn't just about watches and alarms — it powers everything from GPS to stock market trades to data centers.
'Time signals are used literally billions of times each day for everything from setting clocks and watches to ensuring the accurate time stamping of hundreds of billions of dollars of electronic financial transactions,' said Liz Donley, who leads NIST's Time and Frequency Division.
NIST-F4 helps steer the official U.S. time scale, known as UTC(NIST), and contributes to the global timekeeping standard, Coordinated Universal Time (UTC).
Its ultra-precise data helps ensure systems worldwide stay synchronized down to the microsecond.
NIST-F4 didn't happen overnight. It evolved from NIST-F1, the agency's first fountain clock built in the late 1990s.
After a move in 2016 disrupted F1's performance, NIST scientists decided to rebuild the heart of the clock — the microwave cavity — from scratch.
They spent years refining every part, from magnetic coils to optical systems, achieving tolerances as fine as one-fifth the width of a human hair.
"Evaluating a fountain clock... is a slow process because we have to be very conservative,' said physicist Vladislav Gerginov.
NIST has already submitted NIST-F4's data to the BIPM for formal certification. Meanwhile, it runs alongside NIST-F3 to ensure that at least one fountain clock is operating at all times.
'The success of NIST-F4 has renewed NIST's global leadership in primary frequency standards,' Donley said.
And until optical clocks eventually redefine the second, cesium-based fountains like this one will keep global time ticking perfectly.

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