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Time & frequency


Time may be our most measured quantity — and unquestionably one of the most important. We use time to organize our lives, to communicate, to run global industries and to navigate our world. To keep time today, we use atoms — nature’s perfect clocks. Atoms themselves don’t tell time; rather, they absorb and emit specific frequencies of light waves. By building clocks that count those waves with exquisite accuracy, scientists can precisely measure and define the second — the fundamental unit of time — and share time with the world.

The quest to accurately measure time and frequency has pushed the frontiers of science and opened up a host of technological applications. Some technologies, like GPS, are mature and used daily by billions of people. Others are still being developed, such as next-generation gravity and mass sensors and spectrometers for measuring chemicals in the air and signals from space.

NIST, in coordination with the U.S. Naval Observatory, provides official time for the United States. NIST builds and operates the country’s most accurate atomic clocks, which help set the global time scale known as Coordinated Universal Time. Through its own time scale, NIST provides time to the nation and the world via the internet and radio. NIST develops chip-scale atomic clocks and calibrates clocks for customers such as stock exchanges. NIST researchers are working with international colleagues to redefine the second — the fundamental unit of time — using next-generation optical clocks.

NIST has built a broad research program in time and frequency measurement. NIST scientists are using optical atomic clocks to push limits of accuracy and precision and test theories of fundamental physics; they are also building compact atomic and microfabricated optical devices for real-world applications. By controlling atoms with unprecedented precision, NIST researchers are advancing quantum computing, sensing and networking. NIST scientists are also developing state-of-the-art frequency sensors to measure greenhouse gases in the atmosphere and habitable planets outside of the solar system.

The Research

Projects & Programs

Compact Cold Atom Instruments

Our research focuses on the development of novel sensing platforms using cold atomic gases and atomic beams. Laboratory-scale cold atom apparatuses provide some

Frequency Comb Spectroscopy

We use frequency combs based on ultrafast mode-locked lasers to perform precision spectroscopy in the near- and mid-infrared domains, for rapid, high

Additional Resources Links

What Is Time?

Philosophically, what is "time"? Even if we don’t completely understand what time is, we can precisely measure what time it is, thanks to the atomic clock, humankind’s most accurate measurement device. Atomic clocks have revolutionized navigation. Only time will tell us its future applications.

What is time?
What is time?


Keeping Time at NIST

Einstein is reported to have once said that time is what a clock measures. Some say that what we experience as time is really our experience of the phenomenon of entropy, the second law of thermodynamics. Entropy, loosely explained, is the tendency for things to become disorganized. Hot coffee always goes cold. It never reheats itself. Eggs don’t unscramble themselves. Your room gets messy and you

World’s Most Accurate and Precise Atomic Clock Pushes New Frontiers in Physics

Spotlight: Geomagnetic Storm Creates Bright Northern Lights While Also Affecting NIST’s Cesium Clocks

Researchers develop a new type of frequency comb that promises to further boost the accuracy of time keeping

Upcoming Events

2024 Time and Frequency Seminar

Tue, Aug 13 - Thu, Aug 15 2024
NIST Time and Frequency Division's annual seminar covers precision clocks and oscillators, atomic frequency standards