--- title: How Do Atomic Clocks Work? | daily.dev description: Atomic clocks work by isolating individual atoms and exposing them to light tuned to the atoms' resonant frequency. When the light matches this frequency,... canonical: https://daily.dev/posts/how-do-atomic-clocks-work--ebjraivg8 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: How Do Atomic Clocks Work? | daily.dev og:description: Atomic clocks work by isolating individual atoms and exposing them to light tuned to the atoms' resonant frequency. When the light matches this frequency,... og:url: https://daily.dev/posts/how-do-atomic-clocks-work--ebjraivg8 og:image: https://api.daily.dev/og/posts/eBjraIvG8.png og:image:alt: How Do Atomic Clocks Work? og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # How Do Atomic Clocks Work? **[Hacker News](https://daily.dev/sources/hn)** · 6 min read · 0 upvotes · 0 comments ## Summary Atomic clocks work by isolating individual atoms and exposing them to light tuned to the atoms' resonant frequency. When the light matches this frequency, atoms absorb energy and make a quantum jump. By counting the cycles of this resonant light, precise time can be measured. For cesium atoms, one second equals exactly 9,192,631,770 cycles — a definition adopted internationally in 1967. Today's best atomic clocks are so accurate that if they had been running since the Big Bang (13.8 billion years ago), they would have lost or gained less than a second. The first atomic clock was invented in 1949 at what is now NIST. Atomic clocks underpin GPS, telecommunications, financial transactions, and more. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How many cycles of light does it take to define one second using a cesium atomic clock? It takes 9,192,631,770 cycles of light tuned to the cesium atom's resonant frequency to pass through a detector. In 1967, the world's timekeepers formally defined the international second as the time required for exactly that number of cycles, making cesium clocks the basis of the modern time standard. _Precision timing details like this are easy to track down when following physics and computing topics on daily.dev._ ### Why are atomic clocks more accurate than quartz or pendulum clocks? Atomic clocks are more accurate because atoms have no manufactured parts and don't wear out, so all atoms of the same type produce identical, unvarying beats when tuned to their resonant light frequency. Pendulums and quartz crystals, by contrast, vary slightly from one unit to the next and drift over time, making them inherently less stable. _Curious minds comparing measurement technologies can keep exploring physics explainers on daily.dev._ ### How much time drift would the best atomic clocks have accumulated since the Big Bang? The best atomic clocks would have lost or gained less than one second if they had been running continuously since the Big Bang, roughly 13.8 billion years ago. This illustrates their precision, which is billions of times greater than any other type of clock. _Readers fascinated by extreme precision engineering can follow more science deep dives on daily.dev._ ## Community take How the wider developer community reacted, aggregated from 1 discussion and 73 comments across hackernews (as of 2026-09-14). **TL;DR:** Commenters are genuinely fascinated by atomic clocks and their applications, with discussion branching into nostalgic stories about telephone time services, miniaturization challenges, and the physics of what more accurate clocks could enable. The thread is warm and curious rather than critical. **Sentiment:** 65% positive · 25% mixed · 10% skeptical **The case for** - More accurate clocks enable better VLBI radio astronomy resolution and improved gravitational sensing down to centimeter-level altitude differences. - Chip-scale atomic clocks (CSACs) offer major advantages for GPS-denied environments like battlefields and power-constrained satellites. - Radio-synchronized watches that never need manual adjustment are a practical, elegant application of atomic timekeeping. - The article's accessible, beginner-friendly explanation was praised as the kind of content that sparks deeper curiosity. **The pushback** - The article teases 'dreamy new capabilities' from next-gen clocks without explaining what those capabilities actually are. - Radio time-signal coverage marketed as 'worldwide' has significant geographic gaps, making the technology unreliable in many regions. - Miniaturization of atomic clocks has stalled — CSACs still consume too much power for practical battery-powered wearables. **By community** - hackernews (positive): Enthusiastic and wide-ranging discussion spanning nostalgic telephone time services, real-world CSAC applications in space and defense, relativistic effects, and the physics of gravitational sensing — overwhelmingly curious and appreciative in tone. **Hottest debate:** Whether moving objects (not just orbiting ones) produce gravitational waves detectable by atomic clocks sparked a brief but genuine technical disagreement. **Open questions** - What specific new capabilities do next-generation atomic clocks unlock beyond the already extraordinary 1-second-in-13-billion-years accuracy? - How long will radio time-signal infrastructure (WWV, WWVB, DCF77) remain operational compared to Bluetooth/app-based alternatives? - Could atomic clock arrays ever reach sensitivity sufficient to detect neutrinos via their gravitational signature? **Highlights** > Cost, size, weight, and power are definitely things that can be improved on. The atomic clocks you can buy for a lab are big 3U boxes but shrinking it down to something portable is the future. I actually work with one of those chip scale atomic clocks. The goal is to put it in space. If you need precise timing in space, the current state is to lock to a GPS reference clock (just for timing, don't care about position), train an OCXO, and let it drift for a day or two before you require GPS again. OCXOs (and crystal oscillators in general) can be very accurate but the stability is easily affected by temperature swings. So as your satellite goes in and out of the sunlight or as components inside turn on and off, the surrounding temperature changes and can make the clock drift. This isn't a problem on earth since you can always have a GPS receiver running but on a power constrained satellite, this is not ideal. The CSAC gets 100x better thermal stability than even some of the best space-qualified OCXOs. This means you could potentially run for 100x longer before you need to reacquire GPS, assuming the same environment and performance requirements. The CSAC also has a brain inside so potentially you can do all of your characterization on the ground and not even need a GPS receiver onboard. It also requires much less time to become stable after powering on than a normal crystal oscillator. You get the same benefits on the ground, super precise timing for the processors and modems without necessarily needing a GPS receiver. The modern assumption (and pretty much proven in Ukraine) is that GPS will be completely unavailable on a battlefield. Anything portable or battery-powered will likely not be able to make use of newer anti-jam features of GPS (very power hungry) so you need something small, precise, and quick to come online. Modern waveforms often require very tight timing to properly demodulate so having a pocket sized atomic clock solves a lot of problems. > — [wildzzz on hackernews · 1 comments](https://news.ycombinator.com/item?id=49209734) > There are still big leaps, like their optical lattice clock that's sensitive to the gravitational difference caused by tidal effects on the earth's crust. It can detect gravitational differences of a few cm! > — [geerlingguy on hackernews](https://news.ycombinator.com/item?id=49206366) > > What is possible by pushing past that incredibly narrow margin of 1s in 13b years? What dreamy capabilities do we get that we don’t enjoy today? You can measure speed (via special relativity) and altitude (via gravity/general relativity) with atomic clocks [0], so with a more accurate clock, you should be able to calculate your speed/altitude more accurately. GPS is already pretty good at measuring speed/altitude, but its not always very accurate, and it only works if you can receive the satellite's signal. In theory, a more accurate atomic clock would solve both of these problems (as long as you had an equally-accurate clock at a fixed location to compare to). [0]: https://news.ycombinator.com/item?id=16473776 > — [gucci-on-fleek on hackernews](https://news.ycombinator.com/item?id=49206702) > Fun fact, two (very expensive) wristwatches have actual atomic timekeeping in them, instead of just receiving a radio time signal: the Bathys Hawaii Cesium 133, and a few different shaped from Hoptroff London. All released 2013-2015. Not sure what happened then for there to be suddenly two. > — [LeoPanthera on hackernews · 1 comments](https://news.ycombinator.com/item?id=49206139) > > Today’s best atomic clocks are billions of times more accurate and precise than any other type of clock. If they had been running since the Big Bang, 13.8 billion years ago, they would have lost or gained less than a second. Absolutely incredible, but then confused by the next assertion that is made without context: > New kinds of clocks may soon open up capabilities that previous generations could only dream about. What is possible by pushing past that incredibly narrow margin of 1s in 13b years? What dreamy capabilities do we get that we don’t enjoy today? Edit: I’d assumed they were talking about new approaches to making these clocks more accurate, but I wonder if they’re referring to power and form factors? I.E. an atomic clock the size of a grain of rice: https://www.nist.gov/noac/success-story-chip-scale-atomic-cl... > — [r3trohack3r on hackernews · 7 comments](https://news.ycombinator.com/item?id=49206297) **Source threads** - [hackernews](https://news.ycombinator.com/item?id=49129015) · 115 points · 73 comments ## Similar posts on daily.dev - [Singapore Scientists Claim They Built The World’s Most Accurate Atomic Clock](https://daily.dev/posts/singapore-scientists-claim-they-built-the-world-s-most-accurate-atomic-clock-4oparyaej) · The Quantum Insider · 0 upvotes · 0 comments - [Thorium Clocks Start Ticking With Lasers](https://daily.dev/posts/thorium-clocks-start-ticking-with-lasers-0wzzduv9q) · Hackaday · 0 upvotes · 0 comments - [Technology Used by Optical Atomic Clocks May Jump From Lab to Consumer](https://daily.dev/posts/technology-used-by-optical-atomic-clocks-may-jump-from-lab-to-consumer-kvhdaqak1) · The Quantum Insider · 0 upvotes · 0 comments --- Tags: [#quantum-computing](https://daily.dev/tags/quantum-computing) [View this post on daily.dev](https://daily.dev/posts/how-do-atomic-clocks-work--ebjraivg8) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"How Do Atomic Clocks Work?","url":"https://daily.dev/posts/how-do-atomic-clocks-work--ebjraivg8","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/how-do-atomic-clocks-work--ebjraivg8"},"datePublished":"2026-08-07T07:15:29.279Z","dateModified":"2026-09-14T07:16:21.598Z","description":"Atomic clocks work by isolating individual atoms and exposing them to light tuned to the atoms' resonant frequency. 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