1812 lines
137 KiB
Text
1812 lines
137 KiB
Text
<!DOCTYPE html>
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<html lang="en" dir="ltr" prefix="content: http://purl.org/rss/1.0/modules/content/ dc: http://purl.org/dc/terms/ foaf: http://xmlns.com/foaf/0.1/ og: http://ogp.me/ns# rdfs: http://www.w3.org/2000/01/rdf-schema# schema: http://schema.org/ sioc: http://rdfs.org/sioc/ns# sioct: http://rdfs.org/sioc/types# skos: http://www.w3.org/2004/02/skos/core# xsd: http://www.w3.org/2001/XMLSchema# ">
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<head>
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<h1 class="nist-page__title">Think You Know What a Second Is? It Will Likely Change in the Next Decade.</h1>
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<div class="daterange"><time datetime="2023-11-08T12:00:00Z">November 8, 2023</time>
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<span>By: </span>
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<a href="/blogs/taking-measure/authors/tara-fortier" hreflang="en">Tara Fortier</a>
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<img alt="A researcher wearing safety glasses reaches into a box of circuitry and other equipment, which emits a green glow. " height="701" loading="lazy" src="/sites/default/files/images/2023/10/16/tara_fortier_working_in_lab_october_2023.jpg" typeof="foaf:Image" width="1050">
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<figcaption class="nist-image__caption">NIST researcher Tara Fortier aligns optics to maximize the signal coming from an optical clock. The signal is measured by a frequency comb.<div class="nist-image__credit">
|
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<span class="nist-image__credit-label">Credit:</span>
|
||
|
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R. Wilson/NIST
|
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</div></figcaption>
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</figure>
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<p>Measuring and keeping track of time has allowed people to plan and coordinate locally with others for millennia. </p><p>As the world has modernized and our pace of life has increased, our relationship to time has changed. Time has become a scarce commodity. The standardization of time has also become essential for the stability in power grids and for data synchronization over the internet, global travel, and telecommunications. </p><p>In 1960, the second was defined as an international standard unit of measurement for time. Since then, the second has undergone multiple redefinitions. These redefinitions may have happened in your lifetime, and you probably didn’t notice. </p><p>Prior to 1967, the official time reference for the second was the stable but slow rotation of the Earth relative to the cosmos. But Earth’s rotation can slow down and speed up based on the gravitational influence of the Moon and the movement of the outer shell of the Earth. This presents a challenge for accurate timekeeping. </p><p>That’s why, after 1967, the second’s definition changed to one based on the exquisitely stable energy levels in atoms, hence the term “atomic clock.” </p><div class="nist-callout"><p>As an aside, the most recent redefinition of the <a href="/pml/owm/metric-si/si-units" data-entity-type="node" data-entity-uuid="fd133a8e-951b-49fa-b8a8-22d93ab47759" data-entity-substitution="canonical" title="SI Units">International System (SI) of units</a> in 2019, more commonly referred to as the metric system, made it such that all units are defined by the unchanging laws of physics and the constants in nature. This did away with the last “artifacts” in the SI. Previously, the standard of mass, <a href="/si-redefinition/kilogram-introduction" data-entity-type="node" data-entity-uuid="60849a26-85a2-4241-8ad8-a24940c66f02" data-entity-substitution="canonical" title="Kilogram: Introduction">the kilogram</a>, was based on a human-made cylinder of platinum and iridium, whose mass was defined to be one kilogram. </p></div><p>The first atomic clocks were developed in the 1940s and became commercially available in the 1960s. Since then, every decade has seen better than a tenfold improvement in timekeeping performance. Now, if you could wait long enough, the best atomic clocks would lose only one second every 15 billion years!</p><p>With this blog post, I hope to explain how we define time with atoms, how we use timing in modern society, and whether better timing and a future redefinition of the second might impact our lives and modern technology.</p><p>You may have learned to count “one, 1,000” or “two, Mississippi” in school, but the way NIST defines the second with atoms is much more complex. </p><p>Prior to the Industrial Revolution, the best timekeepers were pendulum clocks, the mechanical basis for grandfather clocks. First developed in the late 1600s by Christiaan Huygens, pendulum clocks only lost 15 seconds per day. </p><h2>How Do Clocks Work?</h2> <figure class=" align-right nist-image" role="group">
|
||
<div>
|
||
|
||
<img alt="An ornate antique grandfather clock with roman numerals on its face" height="480" loading="lazy" src="/sites/default/files/styles/480_x_480_limit/public/images/2023/10/16/shutterstock_133127633.jpg?itok=UhnvJoba" typeof="foaf:Image" width="319">
|
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||
|
||
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||
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||
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||
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</div>
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||
<figcaption class="nist-image__caption">In the grandfather clock, the pendulum swings back and forth, or oscillates, under the force of gravity.<div class="nist-image__credit">
|
||
<span class="nist-image__credit-label">Credit:</span>
|
||
|
||
AGCuesta/Shutterstock
|
||
|
||
</div></figcaption>
|
||
</figure>
|
||
|
||
<p>All clocks, including grandfather clocks, atomic clocks and the clocks in your phone, use a periodic oscillation to define time. One second is accumulated by adding together a fixed number of periods of oscillations.</p><p>In the grandfather clock, the pendulum swings back and forth, or oscillates, under the force of gravity. If the pendulum takes 0.5 seconds to swing from left to right and back again, then one second is accumulated after the pendulum completes two periods of oscillation. </p><p>There are two qualities that make a good clock: </p><ul><li>How much its period of oscillation changes or “drifts” over time, causing errors in its definition of one second, and</li><li>How well you can measure the period of oscillation. </li></ul><p>For example, measuring one period of rotation of the Earth relative to the cosmos is very different than measuring the periodic swinging of a pendulum clock. Both of these are different than measuring the energetic oscillations of electrons in an atomic clock. Each of the latter systems requires a different system of measurement, which comes with its unique challenges and measurement errors. </p><p>Both qualities determine how much timing difference, or error, you will have between different clocks over a specified amount of time. In general, the faster the period of oscillation, or the higher the oscillation frequency, the better the resolution you have in defining one second. </p><p>This is similar to how the resolution of a television increases with the number of pixels. The more pixels you have per image, the higher the image quality. If you count every cycle, the more cycles you have per second, the better the timing resolution in a clock. </p><p>Importantly, this is just one of the reasons why the very fast oscillations in atoms yield the best definition of time. </p><h2>How Do Clocks in Laptops and Cellphones Work?</h2><p>While physical oscillation keeps time in large grandfather clocks, which were widely used to keep precise time until the early 1900s, a more portable and higher accuracy clock was developed to meet the more accurate timing needs of modern society. </p>
|
||
<figure class=" align-left nist-image--lightbox nist-image" role="group">
|
||
<div data-lightbox="https://www.nist.gov/sites/default/files/styles/2800_x_2800_limit/public/images/2023/10/16/tara_fortier_portrait_in_lab.jpeg.jpg?itok=5MVIPufa" data-media-id="690271">
|
||
|
||
<img alt="Tara Fortier wears safety glasses as she poses in the lab for a portrait." height="480" loading="lazy" src="/sites/default/files/styles/480_x_480_limit/public/images/2023/10/16/tara_fortier_portrait_in_lab.jpeg.jpg?itok=jHE8W7Kp" typeof="foaf:Image" width="480">
|
||
|
||
|
||
|
||
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||
|
||
|
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</div>
|
||
<figcaption class="nist-image__caption">NIST researcher Tara Fortier<div class="nist-image__credit">
|
||
<span class="nist-image__credit-label">Credit:</span>
|
||
|
||
R. Wilson/NIST
|
||
|
||
</div></figcaption>
|
||
</figure>
|
||
|
||
<p>Currently, all portable electronics use specialized quartz crystals to keep time. If you’re looking at a grandfather clock, you can see the physical pendulum moving to keep the time. The oscillations in quartz, however, result from a much faster mechanical resonances in the crystal that you cannot see. </p><p>In quartz oscillators, the forces between the atoms making up the crystal and other factors determine the tone, or frequency, of the mechanical resonance. It’s similar to a musical instrument. In a piano, for example, the material of the string and how you tension it determine the tone of the musical note. This, combined with the body of the piano, helps determine the quality of the sound. </p><p>Like the pendulum or grandfather clock, quartz oscillators in a phone define one second by accumulating many periods of oscillation of the mechanical resonance. The period of oscillation of quartz in a cellphone is 70,000 times faster than a pendulum clock. It’s also about 125 times higher in frequency than middle C on a piano.</p><p>Today, quartz oscillators only give timing errors of about one second per day. Their small size, amazing accuracy, and low cost have fueled their ubiquity in modern day electronics. As a result, quartz oscillators have become a multibillion-dollar global market. </p><h2>Atomic Clocks and Their Applications in Modern Society</h2><p>An unfortunate feature of all mechanical clocks, including quartz oscillators, is that they tend to drift to some extent or another. This means that a clock can slowly or quickly lose time with respect to other clocks. </p><p>A timing error of one second in 24 hours might not seem important at first thought. However, timing errors among electronic clocks that keep time across the internet can cause problems as mundane as lag times in gaming to as serious as GPS errors for planes. To operate at their highest performance, the clocks in the modern systems I just described have to synchronize themselves to low-drift atomic clocks. </p><div class="nist-callout"><p>Fun fact: The <a href="/pml/time-and-frequency-division/time-distribution/internet-time-service-its" data-entity-type="node" data-entity-uuid="7f3ea4b1-a4dc-4fb8-ab17-8e78e6a217e4" data-entity-substitution="canonical" title="NIST Internet Time Service (ITS)">internet time service at NIST in Boulder, Colorado</a>, which synchronizes electronic devices to U.S. atomic time, receives 100 billion hits per day from devices all over the country. That’s 10 times more hits than the Google search engine servers receive in a day!</p></div><h2>Keeping Time With Atoms</h2><p>Time is defined using atoms in a remarkably similar fashion to quartz oscillators. I like to think of atoms as the world’s most exquisite and precise musical instruments! In atoms, the interplay between the forces exerted by protons, neutrons and electrons — as well as gravitational, electric and magnetic fields — governs the movement and energy of electrons within the atom. </p><div class="nist-callout"><p>The interaction of these forces dictates the atom’s internal resonances, much like string tension determines the notes of a piano. This makes the resonances, or “notes” of the atom, exquisite expressions of the laws of physics. In fact, atomic resonances are used to expand our understanding of physics. Researchers at NIST have used atomic clocks to search for dark matter particles, and to see if our laws of physics are really the same across all space and time. So far researchers haven’t observed any violations to our current laws of physics, but only time will tell (loving the pun?) what we will find as clocks continue to improve. </p></div><p>In some cases, how well the atom’s environment is controlled determines the quality of its resonances. For atomic clocks, we are interested in how pure and how stable a single oscillatory resonance can be. These qualities help determine the resolution and level of error with which we can define the second.</p><p>In physics terminology, adding energy to a system so it can resonate is called an “energetic excitation.” Gravity provides the energy for a pendulum clock, and electrical signals “excite” resonances in quartz oscillators. </p><p>Electromagnetic waves, such as light or radio waves, “excite” atomic resonances. To excite, or “play,” the extremely pure resonance in an atomic clock requires an equally precise electromagnetic wave. The electromagnetic wave, which keeps the atomic tone resonating, can be kept in tune using a system similar to cruise control in a car. </p><p>Because atomic clocks can oscillate 250,000 times faster than quartz oscillators, it takes 250,000 times more cycles to add up to one second of elapsed time. The <a href="/pml/time-and-frequency-division/time-realization/cesium-fountain-atomic-clocks" data-entity-type="node" data-entity-uuid="2886c60e-2b45-48c9-845b-67f69b40e58e" data-entity-substitution="canonical" title="NIST’s Cesium Fountain Atomic Clocks">international unit of time</a>, the SI second, is currently defined as 9,192,631,770 periods of a specific resonance. </p><p>This resonance uses a type of cesium (Cs) atom known as Cs-133. (There are several types or “isotopes” of cesium, depending on the number of neutrons in the nucleus. Cs-133 has 55 protons and 78 neutrons.) </p><p>If you were willing to watch a clock that would work forever, the best Cs-133 atomic clocks would accumulate a timing error of about one second in about 150 million years. </p>
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<figure class=" align-center nist-image--lightbox nist-image" role="group">
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<div data-lightbox="https://www.nist.gov/sites/default/files/styles/2800_x_2800_limit/public/images/2023/10/16/Second-Blog-graphic-092023.png?itok=B12IvoU9" data-media-id="690276">
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<img alt="Illustration shows a grandfather clock floating in outer space surrounded by an atom, a planet, an electronic device. " height="2565" loading="lazy" src="/sites/default/files/images/2023/10/16/Second-Blog-graphic-092023.png" typeof="foaf:Image" width="4251">
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</div>
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<figcaption class="nist-image__caption">The definition of a second will change in the coming years. The good news is you’re unlikely to notice; it’ll just be more precise than before.<div class="nist-image__credit">
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<span class="nist-image__credit-label">Credit:</span>
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N. Hanacek/NIST
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</div></figcaption>
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</figure>
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<h2>An Improved Definition of the Second </h2><p>So, the Cs-133 atomic clock that currently defines the second is very accurate. If a timing error of about one second in about 150 million years is not good enough, clocks based on atoms with resonances at optical frequencies can be used to keep time to a one second error in 15 billion years! </p>
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<figure class=" align-right nist-image--lightbox nist-image" role="group">
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<div data-lightbox="https://www.nist.gov/sites/default/files/styles/2800_x_2800_limit/public/images/2017/03/14/sr-lattice-optical-atomi-clock_opt.jpg?itok=TNEkUj0a" data-media-id="356096">
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<img alt="Strontium Lattice Optical Atomic Clock" height="320" loading="lazy" src="/sites/default/files/styles/480_x_480_limit/public/images/2017/03/14/sr-lattice-optical-atomi-clock_opt.jpg?itok=atNuXOs7" typeof="foaf:Image" width="480">
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</div>
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<figcaption class="nist-image__caption">JILA’s strontium optical atomic clock was made possible by the frequency comb. <div class="nist-image__credit">
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<span class="nist-image__credit-label">Credit:</span>
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The Ye group and Brad Baxley, JILA
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</div></figcaption>
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</figure>
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<p>As I mentioned previously, clocks that oscillate faster have lower timing error, or better time resolution – just like how TVs with more pixels have higher resolutions. </p><p>Because optical clocks have 100 times better time accuracy than atomic clocks based on Cs-133, the international time community is considering using optical atomic resonances to redefine the SI second. The target date for redefinition is set sometime around 2030. </p><p>The international time community has not decided which kind of atom they would use or whether they might even use a combination of clocks based on several different kinds of atoms. Current optical atomic clocks being developed worldwide use at least 28 different kinds of atomic isotopes.</p><h2>The Implications of Redefining the Second </h2><p>The good news is, when the definition does change, you are not likely to notice. The first reason is that, by design, the new definition of the second is supposed to be consistent with the current definition of the second. It will just be much more precise than before. </p><p>The second reason is that our current infrastructure to send timing around the globe will need significant upgrades to support the gains in timing from optical atomic clocks. Fortunately, if the upgrades are made to our satellite and optical network infrastructure, your GPS may be able to pinpoint your location even more accurately. We may also one day see improvements in advanced communications and computing. </p>
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<figure class=" align-center nist-image--lightbox nist-image" role="group">
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<div data-lightbox="https://www.nist.gov/sites/default/files/styles/2800_x_2800_limit/public/images/2023/10/16/tara_fortier_interview_photo_080123jpg.jpg?itok=GsZEVcGq" data-media-id="690281">
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<img alt="A woman in safety glasses sits on a stool in the lab, speaking and gesturing while being filmed by a man holding a video camera. " height="3024" loading="lazy" src="/sites/default/files/images/2023/10/16/tara_fortier_interview_photo_080123jpg.jpg" typeof="foaf:Image" width="4032">
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<figcaption class="nist-image__caption">NIST researcher Tara Fortier is interviewed about NIST’s timekeeping role.<div class="nist-image__credit">
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<span class="nist-image__credit-label">Credit:</span>
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R. Jacobson/NIST
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</div></figcaption>
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<p>Regardless of whether and when the SI second is redefined to optical atomic clocks, the greatest beneficiaries from improvements in timekeeping and measurement will be fundamental research and science. </p><p>It is a rare occurrence that technology takes a step forward and someone doesn’t find some way to take advantage of it. </p><p>As mentioned previously, the exquisitely pure resonances of atomic clocks have been used to search for dark matter particles. Additionally, these clocks can sense how gravity changes across the Earth as a function of altitude. </p><p>That’s because, according to Einstein’s theory of general relativity, time ticks more slowly in stronger gravitational fields. This effect is known as time dilation. The movie Interstellar illustrated this effect when a scientist in a spaceship waited for 23 years for his colleagues who only spent 45 minutes on a planet in the presence of a gravitationally powerful black hole. On Earth, the further you move from its center, the lower the gravitational field you experience. Amazingly, because we can resolve time so precisely with atomic clocks, we can observe the difference in the <a href="/news-events/news/2022/02/jila-atomic-clocks-measure-einsteins-general-relativity-millimeter-scale" data-entity-type="node" data-entity-uuid="79f32bb6-47f6-4784-b6a5-1e9eaece6458" data-entity-substitution="canonical" title="JILA Atomic Clocks Measure Einstein’s General Relativity at Millimeter Scale">“tick rate” for atoms</a> offset in altitude by only 1 millimeter!</p><div class="nist-callout"><p>Fun fact: Because GPS satellites are moving fast compared to people on Earth, and experience a different gravitational field, if we did not correct the onboard clock’s timing for the effects of relativity, <a href="https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html">GPS would accumulate positioning errors of 10 kilometers per day</a> … making it pretty much useless! </p></div><p>You may have seen in the news in 2019 that atomic clocks were used to help create the first image of <a href="https://www.jpl.nasa.gov/edu/news/2019/4/19/how-scientists-captured-the-first-image-of-a-black-hole/">light emitted by a black hole</a>. In this experiment, images from multiple telescopes from around the globe were synchronized to create an effective light-collecting aperture the size of the diameter of the Earth! Importantly, the larger the aperture, the better you can resolve an image.</p><p>In the future, atomic clocks on space-based telescopes, separated by millions of miles, could be used to observe much fainter stars and nebulae and more distant galaxies than we can see today. And atomic clocks on spacecraft could navigate deeper into space because their onboard clocks won’t drift and will require less frequent calibration to clocks on the Earth.</p><p>Hopefully when the second is redefined by optical atomic clocks, you won’t notice. However, the continued improvement in timing through clocks and time measurement will allow us to develop a finer and deeper understanding of nature and the universe. We are a curious species, so scientific advancement will likely be the most important outcome.</p>
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<div class="entity-reference"> <a href="/blogs/taking-measure/authors/tara-fortier" hreflang="en"><img loading="lazy" src="/sites/default/files/styles/thumbnail/public/images/2023/04/07/Fortier%20head%20shot%202022.jpg?itok=SWxT2S_f" width="100" height="80" alt="Tara Fortier" typeof="foaf:Image" />
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<h3 class="nist-teaser__title"><a href="/blogs/taking-measure/authors/tara-fortier"><span>Tara Fortier</span>
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</header>
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<div class="nist-teaser__content">
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<div class="text-with-summary"><p>Tara Fortier is a physicist and project leader in NIST’s Time and Frequency Division. She leads a research group that performs both basic and applied research in the areas of laser source development for precision optical and microwave metrology of atomic clocks and for quantum networks. Fortier is broadly involved with leadership in several scientific organizations, including NIST’s Women in STEM executive board and as a NIST representative to the White House Office of Science and Technology Policy working group on National Quantum Workforce Development, as well as being a fellow for the Optical Society of America and the American Physical Society. <span>Tara is currently on foreign detail in Sevres, France, working at the Bureau International des Poids et Mesures (International Bureau of Weights and Measures) working as a coordinator for outreach and education in using atomic clocks for coordinated universal time.</span></p></div>
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>Related posts</h2>
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<h3 class="nist-teaser__title"><a href="/blogs/taking-measure/high-flying-science-how-and-why-we-sent-refrigerator-halfway-space"><span>High-Flying Science: How and Why We Sent a Refrigerator Halfway to Space</span>
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</a></h3>
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<div class="daterange"><time datetime="2025-02-12T12:00:00Z">February 12, 2025</time>
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<div class="nist-teaser__content">
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<div class="text-with-summary"> NIST-developed tools can study the remnants of the Big Bang and more, and now researchers are working to launch these tools high above the Earth’s atmosphere —
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<div class="entity-reference"> <a href="/blogs/taking-measure/5-concepts-can-help-you-understand-quantum-mechanics-and-technology-without" hreflang="en"><img loading="lazy" src="/sites/default/files/styles/thumbnail/public/images/2023/10/16/tara_fortier_working_in_lab_october_2023.jpg?itok=RkM9HePP" width="100" height="67" alt="A researcher wearing safety glasses reaches into a box of circuitry and other equipment, which emits a green glow. " typeof="foaf:Image" />
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<h3 class="nist-teaser__title"><a href="/blogs/taking-measure/5-concepts-can-help-you-understand-quantum-mechanics-and-technology-without"><span>5 Concepts Can Help You Understand Quantum Mechanics and Technology — Without Math!</span>
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<div class="daterange"><time datetime="2025-02-05T12:00:00Z">February 5, 2025</time>
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<div class="text-with-summary"> Quantum is everywhere, and you can understand the basic quirks of life at the quantum level … no math required.
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<h3 class="nist-teaser__title"><a href="/blogs/taking-measure/safer-skies-fewer-fires-10-ways-nist-impacts-your-daily-life"><span>From Safer Skies to Fewer Fires: 10 Ways NIST Impacts Your Daily Life</span>
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<div class="daterange"><time datetime="2024-12-19T12:00:00Z">December 19, 2024</time>
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<div class="text-with-summary"> If you’ve ever had a medical test, flown on an airplane, or needed to check the time, NIST’s work affects your life every day.
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<article data-comment-user-id="0" id="comment-117761" class="nist-comment js-comment">
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="">CliffG</span></span>
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on
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<span class="nist-comment__date">November 8, 2023 12:40 PM</span>
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<div class="text-long"><p>When I was in high school in the 1960s there were no sound machines to help people sleep. I tuned my Hallicrafters shortwave to 5mhz and went to sleep to "National Bureau of Standards, WWV. At the tone the time will be..." Nerdy.<br />
|
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Years later, in the early 1980's I got snowed in at JFK and was hunting for a soft place to sleep when I was distracted by a man's luggage cart. He had a Hewlett-Packard atomic clock, told me he had just flown back from France where they were doing international time references.<br />
|
||
Later, as a service tech for equipment at an HP facility I was excreted past an area of the building where they were assembling and QA testing atomic clocks. It was a thrill for me, even at ~32 YO. Nerdy.<br />
|
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I wonder how flying from USA to France would have changed the accuracy of the clock? And whether direction of flight would have also affected the time?</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="" content="Taking Measure Editor ">Taking Measure Editor </span></span>
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on
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<span class="nist-comment__date">November 13, 2023 1:49 PM</span>
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<div class="text-long"><p>Hi, Cliff. Thanks for your question. Here's the answer from the author: </p>
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<p>First of all, I love hearing about your history with atomic clocks and sleep.... I never thought of WWV as a sleep app! Regarding timing differences between a ground clock and a clocks transported from the U.S. to France via plane, there would be a time difference between a ground clock at the nanosecond level due to the effects of special relativity. The magnitude and sign of the time difference would depend on whether the clock is flown along or against the rotational direction of the earth. This time dilation effect, which was predicted by Einstein in the early 1900's, is often termed the “twin paradox.” It was first officially verified for macroscopic Cs atomic beams clocks flown on a Concorde aircraft in the 1970's. If you are interested in learning more, you can read the original paper published in Science in 1972: J.C. Hafele and R. E. Keating, Science 177, 166 (1972).</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="">JeffK</span></span>
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on
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<span class="nist-comment__date">November 15, 2023 3:23 PM</span>
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<div class="text-long"><p>My first exposure to Atomic Clocks was when I was in Metrology (PMEL) in the USAF in Japan, in 1981. AGMC traveled with an HP atomic clock and went so far as to seat it next to the Auditor, complete with Airline Ticket for 'Mr. Clock'. Aside from the effects of Special Relativity, were there other physical variable taken into consideration (Shock, Vibration, Temperature, Barometric pressures) and correction factors applied?</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="" content="Taking Measure Editor">Taking Measure Editor</span></span>
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on
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<span class="nist-comment__date">November 28, 2023 1:55 PM</span>
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<span class="nist-comment__parent">| Replied to <a href="/comment/117811#comment-117811" class="permalink" rel="bookmark" hreflang="en">My first exposure to Atomic…</a></span>
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<div class="text-long"><p>Hi, Jeff. Thanks for your question. Here's the response from the author: </p>
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<p>Absolutely! The effects of multiple physical variables are taken into account to ensure the highest performance operation of the clocks. Environmental engineering is critical to minimize the effects of vibration and acoustic noise, which result in movement (Doppler shifts) of the atoms relative to the electromagnetic fields that excite and are stabilized to the atomic transition. This is especially needed for clocks experiencing the noisy physical environment of an aircraft. Additionally, amazing efforts are made at controlling, measuring and understanding how stray fields (electric fields, magnetic fields, electromagnetic fields due to light and heat) change the atomic clock transition frequency. In the end, controlling and understanding the environment "felt" by the atoms and the electro-magnetic fields that excite them strongly determines the accuracy we can achieve with atomic clocks.</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="">wewe</span></span>
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on
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<span class="nist-comment__date">February 8, 2024 9:27 PM</span>
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<div class="text-long"><p>good read</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="">อนุรักษ์ ศรีจันทรา</span></span>
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on
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<span class="nist-comment__date">November 4, 2024 9:18 AM</span>
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<div class="text-long"><p>เรียนท่านอาจารย์ว่า กระผมขอสอบถามถึงหน่วยตามนี้ครับ "อณู โมเลกุล อะตอม สะสาร พลังาน<br />
|
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กับ ประจวบ พบเจอ ประดิษฐิ์ และ เวลา อดีต ปัจจุบัน อนาคต คือสิ่งใดสัมพันธ์กันบ้างครับ<br />
|
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(นาย อนุรักษ์ ศรีจันทรา)ผู้สอบถามและเรียนรู้.</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="" content="Taking Measure Editor ">Taking Measure Editor </span></span>
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on
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<span class="nist-comment__date">November 4, 2024 9:38 AM</span>
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<mark class="hidden nist-comment__new" data-comment-timestamp="1730731118"></mark>
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<span class="nist-comment__parent">| Replied to <a href="/comment/156771#comment-156771" class="permalink" rel="bookmark" hreflang="en">เรียนท่านอาจารย์ว่า…</a></span>
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<div class="text-long"><p>Google translation of this comment:<br />
|
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To the teacher that I would like to inquire about the following units: "molecule, molecule, atom, substance, energy."<br />
|
||
With Prachuap, met, invented, and time, past, present, and future, what are they related to?<br />
|
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(Mr. Anurak Srichantra) who inquires and learns.</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="">Richard Casey</span></span>
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on
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<span class="nist-comment__date">November 4, 2024 9:31 AM</span>
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<div class="text-long"><p>In all likelihood, time is an emergent property. It’s fascinating to see NISTs contributions to research in time.</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="">Rob Smith</span></span>
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on
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<span class="nist-comment__date">November 4, 2024 9:53 AM</span>
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<div class="text-long"><p>When you have the most accurate clock in the world, against what standard do you calibrate it?</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="" content="Taking Measure Editor">Taking Measure Editor</span></span>
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on
|
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<span class="nist-comment__date">November 4, 2024 4:28 PM</span>
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<mark class="hidden nist-comment__new" data-comment-timestamp="1730755734"></mark>
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<span class="nist-comment__parent">| Replied to <a href="/comment/156786#comment-156786" class="permalink" rel="bookmark" hreflang="en">When you have the most…</a></span>
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<div class="text-long"><p>Hi, Rob. Thanks for your comment. We published a blog post today on atomic clocks that discusses this - <a href="https://www.nist.gov/blogs/taking-measure/how-atomic-clocks-have-changed-our-world">https://www.nist.gov/blogs/taking-measure/how-atomic-clocks-have-change…</a>.</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="">Rob Smith</span></span>
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on
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<span class="nist-comment__date">November 4, 2024 4:25 PM</span>
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<div class="text-long"><p>A second question: do passing gravitational waves affect the accuracy of this clock? If so, does the gravitational background 'murmor' of compact objects merging throughout the Universe constitute a source of statistical error for a clock which loses only one second in 15 gy?</p>
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<span class="nist-comment__author"><span lang="" typeof="schema:Person" property="schema:name" datatype="" content="Taking Measure Editor">Taking Measure Editor</span></span>
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on
|
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<span class="nist-comment__date">November 6, 2024 10:20 AM</span>
|
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<mark class="hidden nist-comment__new" data-comment-timestamp="1730906441"></mark>
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<span class="nist-comment__parent">| Replied to <a href="/comment/156791#comment-156791" class="permalink" rel="bookmark" hreflang="en">A second question: do…</a></span>
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<div class="text-long"><p>Hi, Rob. Thank you for your question. I'm posting this reply on behalf of Tara Fortier: </p>
|
||
<p>That is a great question. Atomic clocks are definitely sensitive to gravitational effects. In fact, moving an atomic clock vertically in earth's gravitational field by 1 cm will change how fast it ticks by 1 part in 10^(18), representing a statistical effect that needs to be accounted for to assure the highest clock accuracy. However, the effect of gravitational waves on clock timing is much weaker due to the vast distance they travel to get to earth. To be sensitive to gravitational waves, atomic clocks would need to reach fractional resolutions better than 1 part in 10^(20) within 1 second of averaging, which is one 10,000 times better than that of the best clocks today. While gravitational waves are not an issue for current clocks, uncertainties in the knowledge of earth's gravitation field make it challenging to compare clocks globally at levels near 1 part in 10^(17). Local relative measurements of the earth's geoid have better resolution, contributing a systematic uncertainty to clocks closer to 10^(-19). (S. Kolkowitz, I. Pikovski, N. Langellier, M. D. Lukin, R. L. Walsworth, and J. Ye "Gravitational wave detection with optical lattice atomic clocks," Phys. Rev. D 94, 124043 – Published 27 December 2016)</p>
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