The NIST-F1 atomic clock in Boulder, Colorado

The United States’ method of keeping time was already very accurate but yesterday, took a giant leap forward with the introduction of the NIST-F2 atomic clock. Scientists at the National Institute of Standards and Technology (NIST) have been building the NIST-F2 for about 10 years in hopes of replacing the aging F1 which has been used to keep the official U.S. time since 1999. The new NIST-F2 is three-times more accurate that its predecessor.  The NIST-F2 clock is used to keep the official time in the United States and is shared with the International Bureau of Weights and Measures in Paris, France.

Why is accurate time important?

Accurate time is very important for businesses such as electrical power grids, GPS satellite systems, and telephone networks (which includes setting the watch on your smartphone). For these industries, equipment must be kept in perfect synchronization in order to work properly.  The only way to do that is to make sure the time set on each piece of equipment is near perfect.  This can only be done with an atomic clock.  The NIST-F2 atomic clock is expected to lose only 1/1,000,000,000,000th of a second each day. That means the clock would only lose only one entire second every 300,000,000 years!

How does an atomic clock work?

The NIST-F2 and F1 atomic clocks work by measuring the microwave frequency that is most optimal for pushing the cesium atoms into an excited state. To do this, a laser traps about 10-million cesium atoms which are then propelled upward, using another set of lasers, into a sealed (and cooled) 3-foot high microwave chamber. While inside the microwave chamber, yet another laser is used to “excite” the cesium atoms causing them to fluoresce (emit photons). The frequency of the microwave that produces the maximum fluorescence of the cesium atoms inside the microwave chamber is used to define what a true “second” is.

Illustration of the inner workings of an atomic clock like the NIST-F2

Once the time is determined by the atomic clock, it is sent around the world using shortwave radio broadcasts. One particular radio station broadcasts at 60 kilohertz which is sufficient to ensure the accuracy of the time sent to about one millisecond.

An atomic clock is an atomic clock – why is F2 any better?

The F2 was made more accurate than the F1 by lowering the temperature that the clock runs in. The F1 ran in an environment that was 27 degrees Celsius. The F2 operates in an enclosure that is cooled to -193 degrees Celsius.  This causes the cesium atoms to move slower and hence, makes them easier to measure. As such, the NIST-F2 has been certified as the world’s most accurate clock.

For now, both NIST-F1 and F2 will continue running at the National Institute of Standards and Technology lab in Boulder, Colorado. Free software is available at You can download the software and use it to set the time on your computer to NIST-F2’s standard.

And what does this have to do with time travel?

Interestingly, according to Wired Magazine:

“Researchers think they are reaching the limit of accuracy with the technology. Any clock that is more precise would begin to feel subtle effects explained by Einstein’s theory of relativity. Clocks experience a gravitational warping from massive objects. The Earth, an extremely massive object, causes clocks closer to its surface to run slower relative to those above it. Cesium atoms in fountain clocks actually experience time differently at the top of the 3-foot chamber than at the bottom. An extremely precise measurement device would be confused by this slight difference, making its time keeping inaccurate.”


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