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The Atomic Clock, Accurate To 1 Second Per 300,000 Years, Turns 62 Today

The Atomic Clock, Accurate To 1 Second Per 300,000 Years, Turns 62 Today Featured Articles

Louis Essen & Jack Perry with the first atomic clock in 1955. Image Source: National Physical Laboratory

Measuring distance, speed, even something as intangible as sound, I can sort of wrap my head around. But time flows in mysterious ways our minds often have trouble comprehending. At times it flies, while when we’d want it to the least, it appears to stand still. So, measuring it accurately understandably remains one of the greatest fascinations, and not just for such philosophical reasons, but scientific ones as well. The most accurate of all timekeepers, the Atomic Clock, is turning 62 today, so let’s look back at how it began ticking and buzzing away on June 3, 1955.

The Atomic Clock, Accurate To 1 Second Per 300,000 Years, Turns 62 Today Featured Articles

A schematic of the first Caesium Atomic Clock. Image Source: National Physical Laboratory

The Early Beginnings

Thousands of years ago, it all started with the most simple of observations, like the repetition of days and nights, or the periodic succession of seasons – easy enough to keep track of. Everything else, like weeks, months, or hours and seconds were much more challenging to accurately quantify. I am working on an article that will discuss the history of time and timekeeping from a watch enthusiast’s perspective, so let us now skip those few thousand words (and years) and get to how atomic timekeeping came to be.

The Atomic Clock, Accurate To 1 Second Per 300,000 Years, Turns 62 Today Featured Articles

Salvador Dalí: The Persistence of Memory. Image Source: Museum of Modern Art

Time, by definition, is the indefinite, continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future. An operational definition of time comes from observing a certain number of repetitions of a standard cyclical event (like the passage of a free-swinging pendulum) which in turn constitutes one standard unit. In other words, to measure time, we need to split it up into equally long and repetitive events and then count said events.

The Atomic Clock, Accurate To 1 Second Per 300,000 Years, Turns 62 Today Featured Articles

Isidor Isaac Rabi

A second used to be defined as 1/86,400 of the mean solar day, but irregularities in the Earth’s rotation make this measurement of time highly imprecise. The more accurate time we want to keep, the smaller and more consistently repetitive segments we have to split it into.

The idea of using atomic transitions to measure time was suggested by Lord Kelvin in 1879, but from idea to realization, it was still a very long way to go. As we will see, magnets and magnetism will play a role as well, so we’ll mention here that it was Isidor Rabi, who further developed the theory behind magnetic resonance, to first suggest in 1945 that atomic beam magnetic resonance might be used as the basis of a clock.

The Atomic Clock, Accurate To 1 Second Per 300,000 Years, Turns 62 Today Featured Articles

Ammonia Master Atomic Clock. Image Source: NIST

The first ever atomic clock came to be shortly after, when the U.S. National Bureau of Standards (NBS, now NIST) built an ammonia maser device in 1949. Funnily enough – but perhaps not surprisingly – it was less accurate than existing quartz clocks and was created more as a demonstration of the concept.

The Atomic Clock, Accurate To 1 Second Per 300,000 Years, Turns 62 Today Featured Articles

The first atomic clock, on display at the Science Museum, London

The First Practical Atomic Clock By Louis Essen & Jack Perry

British physicist Louis Essen earned his PhD and Doctor of Science from the University of London before becoming interested in finding ways to move timekeeping away from traditional definitions expressed in terms of the period of the Earth’s rotation.

Fascinated by the possibility of using the frequency of atomic spectra to improve time measurement, he learned that the feasibility of measuring time using caesium as an atomic reference had already been demonstrated by the NBS. In 1955, in collaboration with Jack Parry, he developed the first practical atomic clock by integrating the caesium atomic standard with conventional quartz crystal oscillators to allow calibration of existing time-keeping.

The Atomic Clock, Accurate To 1 Second Per 300,000 Years, Turns 62 Today Featured Articles

1.3 kilograms of Cesium-133 sealed in a glass container. Via:

By using microwaves to excite electrons within atoms of caesium from one energy level to another, Essen was able to stabilize the microwaves at a precise and reproducible frequency. A lot like the swinging of a pendulum, Essen’s prototype atomic clock relied on this frequency to keep track of the passing of time.



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  • Simon_Hell

    So I guess the obvious question is, how do they know it loses one second every 300 000 years, if its only 62 years old. The second question is – who gives a shit. Seriously, nobody. Too bad they didnt invest all this energy into something worthwhile. Like disposable plastic bags, or some sustainable replacement of plastic all together.

    • David Bredan

      You need not operate a clock/watch through its lifetime to be able to calculate its accuracy. Second, I care, so there goes your (quite sad) “nobody gives a shit” assessment. I honestly cannot see the point in spreading this attitude, people who care won’t stop caring because of it. Third, eco-friendly plastic bags have already been invented and are used in more developed countries.

      • Simon_Hell

        Had they started working on those bags a lot sooner, instead of improving the accuracy of a pointless gizmo, the world wouldnt be in the irreversible ecological shit it is now. But hey, at least we know that when we cease to exist, we’ll know exactly what time is. My point is that this is an example of a massive waste of human talent and energy.

        • David Bredan

          Personally, I never opposed to occupations not entirely (or at all) beneficial for humanity – not everyone can heal the wounded, invent vaccines or feed those starving. We all can and should make a positive difference in our own ways though.
          Back on topic, this invention gave the world GPS (just to focus on the most important of all its consequent tools and inventions), which helped improve aviation which in turn allows people and goods to travel freely, or the ambulance to get to you and then to hospital faster when you’ll inevitably need it. This (not to mention all the other stuff) is objectively useful in one way or another for everyone in the developed and developing worlds and it’s all because we absolutely have to know and be able to synchronize accurate time.
          Last, it’s not like scientists/physicists who researched the atomic clock could just go and invent something else, it very clearly doesn’t work that way.

        • Ummm..that’s like asking why Marconi wasted his time with those silly wireless contraptions instead of finding a cure for polio.

          • Simon_Hell

            Thanks man. You get what I’m saying.

          • Quite the contrary. I couldn’t have been more sarcastic.

        • Omegaboy

          Ah, now we have the Talent Police. Good thing you weren’t in uniform when Bach, Rembrandt, and T. S. Eliot were around.

        • Sheez Gagoo

          If you don’t like pointless gizmos,why are you on a blog which is all all about pointless gizmos? This is the pointless-gizmo-blog par excellence. Isn’t there a save-the-world-blog around?

        • Do you honestly thing production of plastic bags would be possible without accurate timekeeping? Heck, you can’t even make a 3 minute egg without knowing how long 3 minutes is. Next…

          Oh yeah, Simon – I forgot to ask: what life or eco saving things have you invented? Or are you wasting your time on endeavors even less beneficial to the world than horology?

    • Mikita

      They should have consulted you where to invest the energy..

    • IG

      Living in your mum’s basement must diminish your need and understanding of timekeeping, nights and days must be blurred there. But in the outside world very accurate timekeeping is a must for some important systems.

    • TheChuphta

      So I guess the obvious question is, why don’t you invent disposable trolls and just kill yourself?

    • SuperStrapper

      Your posts are bad and you should feel bad.

  • Mikita

    Damn, so it’s 0.207 ms inaccurate already

  • Word Merchant

    Exactly when today does it turn 62?

    • David Bredan

      13:43.02 UTC, give or take about 0.000207 seconds.

  • Marius

    I am extremely surprised by the fact that the author of this article has wilfully and deliberately “forgotten” to mention that Hodinkee & Ben Clymer are working on a new, state-of-the-art version of the atomic clock. This improved atomic clock should be available on the Hodinkee Shop as a limited edition, towards the end of September. The H Clock will be manufactured at a secret location in Europe (the same secret location where the $12,000 hourglass is produced), and it will be available as an application-piece only.

    Here is a picture of the H Team working on this project:

    Here is a picture of how the new H Clock will be delivered to the lucky owners:

    And here is a picture of the first buyer of the H Clock:

  • Julian Guitron

    Very interesting!! I was aware that the definitive accuracy in our phones is based on atomic time but never had the chance to look at it in some detail. Thanks for the review.

    I think scientifically exact time measurement should continue its evolution pretty much like any other science… I remain happy with my +/- 5 secs with my mechanical movements if I’m lucky ? – always good to know that if you need down to the second exactness you can just pull your cell out to check… in part thanks to the atomic clocks.

    Thanks again!

  • Phil leavell

    I’m just waiting for the wrist version to come out. I hope Corum gets to pick the colors of all the sprockets and gears. I’m sure it will be snapped up by the Swatch group and redesign by the Chinese, and then sold on the shopping channel for 19.95 🙂

    • IanE

      It’s there – here is Hodinkee (oh no!) on the prototype :-

      • Phil leavell

        Maybe Hublot getting on the design and bring it out sooner

    • David Bredan
      • Saul Sloota

        Yes. More wearable than Bathys.

        • Phil leavell

          Thank you for your reply. To date I only have mechanical watches and I really do like the looks of the grand Seiko 9f quartz

      • Phil leavell

        sorry was away. With all your vast knowledge of watches. What is the most accurate non satellite/ Telecom assist watch made

        • David Bredan

          Citizen CTQ57-0953 Chronomaster, Grand Seiko 9F, Breitling B50 SuperQuartz and a few others with thermocompensated, high-end quartz movements will be the most accurate – perhaps apart from the Hoptroff I linked to above.

  • I have always been fascinated by atomic timekeeping. Its evolution has led to some pretty fantastic modern technology. (The author mentioned the GPS system, which could not function without it.) And for may years have used a link to the NIST to set my watches. Thanks for the article David.

  • edwin

    Very interesting article. Well done! David’s articles are always well researched and written.

    • David Bredan

      Thanks, Edwin, really appreciate it!

  • Lincolnshire Poacher

    Great article. Thank you.

    • David Bredan

      Thank you!

  • ConElPueblo

    This was way out of my league in regards to understanding the principles – but a fun read!

    One thing, though. Pedantic as I know it to be, that ABTW continues to state that something is “X times more accurate” than something else bothers me. You don’t measure accuracy, you measure INaccuracy. Deviation. Therefore, said movement/technology is (for instance) “a third as inaccurate”, not “three times as accurate”.


    • David Bredan

      Thank you for your feedback. We do measure deviation, but something with less deviation is more accurate – sounds logical to me. Nevertheless, I’ll try and keep your feedback in mind, but I believe it really isn’t something that adds much to help make the point clearer and the way we say it leaves no room for confusion either. Cheers!

      • ConElPueblo

        Oh, I would be very surprised if anyone here didn’t understand the meaning. In my eyes it just looks odd. It’s the equivalent of saying that something is “X times smaller” than something else – it is the other way around 🙂

  • Brosan55

    Great article! Very interesting. Thanks.

  • Mischa

    Brilliant article. Not an easy thing, to make it this accessible. I couldn’t think of a more appropriate ABTW author to produce this.

  • earthtodan

    +/- 1 nanosecond per month won’t do, I keep a very busy schedule. Will have to go with Strontium.

    • Hmmm

      Well said!

  • Marco Sampuel

    Excellent article David, I can’t wait to read the “A Brief History Of Time & Timekeeping” article, it for sure will be very interesting.

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