Time & frequency

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<div class="nist-block nist-block--no-margin"> <div class="entity-reference"> <img loading="lazy" src="/web/20240205000156im_/https://www.nist.gov/sites/default/files/images/2023/10/10/16pml015_ytterbium_clock_n_phillips_hr_1200x248.jpg" width="2400" height="496" alt="black background. brightly colored lasers shooting in multiple directions." typeof="foaf:Image"/> </div> </div> </div> <div class="nist-section-header__top grid-container"> <a href="/web/20240205000156/https://www.nist.gov/physics">Physics</a> </div> <div class="nist-section-header__sub"> <div class="nist-section-header__main grid-container"> <div class="grid-row"> <div class="nist-section-header__title"> <h1 class="nist-page__title">Time & frequency</h1> </div> </div> </div> </div> </div> </div> <div class="grid-container"> <div class="nist-page__region nist-page__region--topic-description padding-top-4 margin-top-1"> <div class="nist-region-heading"> <h2>Overview</h2> </div> <div class="grid-row"> <div class="tablet:grid-col-8 padding-right-5 margin-bottom-4"> <div class="text-with-summary"> <p><span><span><span>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. </span></span></span></p> <p><span><span><span>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.</span></span></span></p> <p><span><span><span>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.</span></span></span></p> <p><span><span><span>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.</span></span></span></p> </div> </div> <div class="tablet:grid-col-4"> <div class="nist-block nist-block--no-margin"> <h2 class="nist-block__title">Featured Content</h2> <div class="nist-field nist-field--label-hidden nist-field--link-list link font-sans-sm"> <div class="nist-field__items"> <div class="nist-field__item"><a href="https://web.archive.org/web/20240205000156/https://www.time.gov/">Official U.S. Time</a></div> <div class="nist-field__item"><a href="/web/20240205000156/https://www.nist.gov/pml/time-and-frequency-division">NIST Time and Frequency Division</a></div> <div class="nist-field__item"><a href="/web/20240205000156/https://www.nist.gov/pml/time-and-frequency-division/popular-links/time-frequency-z">Time and Frequency: A to Z</a></div> <div class="nist-field__item"><a href="/web/20240205000156/https://www.nist.gov/pml/time-and-frequency-division/popular-links/web-clock-faq">Time and Frequency Frequently Asked Questions (FAQs)</a></div> <div class="nist-field__item"><a href="/web/20240205000156/https://www.nist.gov/si-redefinition/second-introduction">The SI Second</a></div> <div class="nist-field__item"><a href="/web/20240205000156/https://www.nist.gov/how-do-you-measure-it/how-do-you-measure-second">How Do We Measure Time?</a></div> <div class="nist-field__item"><a href="/web/20240205000156/https://www.nist.gov/pml/time-and-frequency-division/time-services/calibrations-services-time-and-frequency-division">Calibration Services in the Time and Frequency Division</a></div> </div> </div> </div> </div> </div> </div> </div> <div class="nist-page__region nist-page__region--main"> <div class="nist-block"> <div class="grid-container margin-y-5"> <div class="paragraph paragraph--type--topic-research paragraph--view-mode--default"> <div class="nist-region-heading"> <h2>The Research</h2> </div> <div class="grid-row"> <div class="tablet:grid-col-8 padding-right-5 margin-y-2"> <h2 class="nist-block__title">Projects & Programs</h2> <article about="/programs-projects/compact-cold-atom-instruments" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20240205000156/https://www.nist.gov/programs-projects/compact-cold-atom-instruments" hreflang="en"><img loading="lazy" src="/web/20240205000156im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2023/04/26/chip-scale-atomic-beam-clock.png?itok=DbhUyBCk" width="100" height="68" alt="chip scale atomic beam clock" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20240205000156/https://www.nist.gov/programs-projects/compact-cold-atom-instruments"><span>Compact Cold Atom Instruments</span> </a></h3> <div class="nist-teaser__type"> <div class="nist-badge display-inline-block margin-y-1 nist-badge--blue boolean">Ongoing</div> </div> </header> <div class="nist-teaser__content"> <div class="text-long"> Our research focuses on the development of novel sensing platforms using cold atomic gases and atomic beams. Laboratory-scale cold atom apparatuses provide some </div> </div> </div> </article> <article about="/programs-projects/time-measurement-and-analysis-service-tmas" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20240205000156/https://www.nist.gov/programs-projects/time-measurement-and-analysis-service-tmas" hreflang="en"><img loading="lazy" src="/web/20240205000156im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2017/12/08/nistdo_chassis.png?itok=4Ns8TBSa" width="100" height="55" alt="NIST disciplined clock chassis" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20240205000156/https://www.nist.gov/programs-projects/time-measurement-and-analysis-service-tmas"><span>Time Measurement and Analysis Service (TMAS)</span> </a></h3> <div class="nist-teaser__type"> <div class="nist-badge display-inline-block margin-y-1 nist-badge--blue boolean">Ongoing</div> </div> </header> <div class="nist-teaser__content"> <div class="text-long"> The NIST Time Measurement and Analysis Service (TMAS) was designed to serve any organization that is required to maintain an accurate local time standard. The </div> </div> </div> </article> <article about="/programs-projects/frequency-comb-spectroscopy" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20240205000156/https://www.nist.gov/programs-projects/frequency-comb-spectroscopy" hreflang="en"><img loading="lazy" src="/web/20240205000156im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/pml/div688/grp80/combspec1.jpg?itok=zJKb2eXb" width="100" height="67" alt="CombSpec1" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20240205000156/https://www.nist.gov/programs-projects/frequency-comb-spectroscopy"><span>Frequency Comb Spectroscopy</span> </a></h3> <div class="nist-teaser__type"> <div class="nist-badge display-inline-block margin-y-1 nist-badge--blue boolean">Ongoing</div> </div> </header> <div class="nist-teaser__content"> <div class="text-long"> We use frequency combs based on ultrafast mode-locked lasers to perform precision spectroscopy in the near- and mid-infrared domains, for rapid, high </div> </div> </div> </article> <div class="link-list"><a href="/web/20240205000156/https://www.nist.gov/laboratories/projects-programs/topic/249301">View All Projects/Programs</a></div> </div> <div class="tablet:grid-col-4 margin-y-2"> <h2 class="nist-block__title">Additional Resources Links</h2> <div class="nist-field nist-field--label-hidden nist-field--link-list link nist-field--link-list font-sans-sm"> <div class="nist-field__items"> <div class="nist-field__item"><a href="/web/20240205000156/https://www.nist.gov/publications/search?k=&d%5Bmin%5D=&d%5Bmax%5D=&t=&a=&s=All&ta%5B0%5D=249301&ta%5B1%5D=249301&n=">Publications</a></div> </div> </div> </div> </div> </div> </div> <div class="grid-container margin-y-5"> <div class="paragraph paragraph--type--topic-text paragraph--view-mode--default"> <div class="nist-region-heading"> <h2> What Is Time? </h2> </div> <div class="tablet-lg:grid-col-8 padding-right-5"> <div class="text-long"><p>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.</p> <figure class=" align-center nist-video" role="group"><div data-media-id="389686"> <div class="video-embed-field"><div class="video-embed-field-lazy" data-video-embed-field-lazy="<div class="video-embed-field-provider-nist-kaltura video-embed-field-responsive-video"><iframe width="854" height="480" frameborder="0" allow="autoplay *; fullscreen *; encrypted-media *" allowfullscreen="allowfullscreen" src="https://www.kaltura.com/p/684682/sp/68468200/embedIframeJs/uiconf_id/31013851/partner_id/684682?iframeembed=true&amp;entry_id=0_ezc4co72?iframeembed=true&amp;entry_id=0_ezc4co72&amp;flashvars%5BautoPlay%5D=1"></iframe> </div> "><img alt="What is time?" loading="lazy" src="https://web.archive.org/web/20240205000156im_/https://cdnsecakmi.kaltura.com/p/684682/sp/68468200/thumbnail/entry_id/0_ezc4co72/width/1280" typeof="foaf:Image"/><button class="video-embed-field-lazy-play"></button> <div class="video-embed-field-lazy-title">What is time?</div> </div> </div> </div> <figcaption class="nist-image__caption"></figcaption></figure></div> </div> </div> </div> <div class="grid-container margin-y-4"> <div class="nist-region-heading"> <h2>News</h2> </div> <div class="margin-bottom-5"> <div class="entity-reference"> <div class="nist-card nist-card--horizontal nist-card--horizontal-full"> <div class="nist-card__inner"> <div class="nist-card__image"> <a href="/web/20240205000156/https://www.nist.gov/blogs/taking-measure/keeping-time-nist"> <div class="entity-reference"> <img loading="lazy" src="/web/20240205000156im_/https://www.nist.gov/sites/default/files/styles/600w_x_360h/public/images/2020/06/18/nist_physicist_elizabeth_donley_featured%20image.jpg.webp?itok=WvT8tD3X" width="600" height="360" alt="NIST physicist Elizabeth Donley and Compact Atomic Clock" typeof="foaf:Image"/> </div> </a> </div> <div class="nist-card__title"> <h3><span>Keeping Time at NIST</span> </h3> </div> <div class="nist-card__content"> <div class="text-with-summary"> 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 </div> </div> <div class="nist-card__links"> <div class="nist-card__button"> <a href="/web/20240205000156/https://www.nist.gov/blogs/taking-measure/keeping-time-nist" class="usa-button ">Read more</a> </div> </div> </div> </div> </div> </div> <div class="paragraph paragraph--type--dynamic-news-list-topic paragraph--view-mode--default"> <div class="views-element-container"><div class="js-view-dom-id-29b82f2d627d750ba081d4aa240650da4de7bdbdc058a5a096f3fcfc18215229"> <div class="grid-row grid-gap-2"> <div class="nist-card tablet:grid-col-4 nist-card--topic "> <div class="nist-card__inner"> <div class="nist-card__image"> <a href="/web/20240205000156/https://www.nist.gov/news-events/news/2023/11/do-bump-nist-scientists-perfect-miniaturized-technique-generate-precise"> <div class="entity-reference"> <img loading="lazy" src="/web/20240205000156im_/https://www.nist.gov/sites/default/files/styles/800w_x_400h/public/images/2023/11/28/ring-microresonators.png.webp?itok=3Demkmns" width="800" height="400" alt="ring microresonators illustration" typeof="foaf:Image"/> </div> </a> </div> <div class="nist-card__title padding-y-5"> <h3><span property="schema:name">Do the Bump: NIST Scientists Perfect Miniaturized Technique to Generate Precise Wavelengths of Visible Laser Light</span> </h3> </div> <div class="nist-card__links"> <div class="nist-card__button"> <a href="/web/20240205000156/https://www.nist.gov/news-events/news/2023/11/do-bump-nist-scientists-perfect-miniaturized-technique-generate-precise" class="usa-button ">Read more</a> </div> </div> </div> </div> <div class="nist-card tablet:grid-col-4 nist-card--topic "> <div class="nist-card__inner"> <div class="nist-card__image"> <a href="/web/20240205000156/https://www.nist.gov/news-events/news/2023/06/nist-designed-photonic-chip-transforms-single-beam-light-multiple-beams"> <div class="entity-reference"> <img loading="lazy" src="/web/20240205000156im_/https://www.nist.gov/sites/default/files/styles/800w_x_400h/public/images/2023/06/30/photonic-chip.png.webp?itok=9KAqljze" width="800" height="400" alt="photonic chip illustration" typeof="foaf:Image"/> </div> </a> </div> <div class="nist-card__title padding-y-5"> <h3><span property="schema:name">NIST-Designed Photonic Chip Transforms a Single Beam of Light Into Multiple Beams, Each With a Panoply of Different Properties</span> </h3> </div> <div class="nist-card__links"> <div class="nist-card__button"> <a href="/web/20240205000156/https://www.nist.gov/news-events/news/2023/06/nist-designed-photonic-chip-transforms-single-beam-light-multiple-beams" class="usa-button ">Read more</a> </div> </div> </div> </div> <div class="nist-card tablet:grid-col-4 nist-card--topic 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