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Science

Nist: New Optical Clock More Accurate Than Cesium 44

Posted by chrisd from the lonely-exhibitionsist-ion dept.
LordPhatal writes "NIST researchers have demonstrated a new kind of atomic clock that has the potential to be up to 1,000 times more accurate than today's best clock. The new clock is based on an energy transition in a single trapped mercury ion.
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Nist: New Optical Clock More Accurate Than Cesium More

Nist: New Optical Clock More Accurate Than Cesium

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  • no excuse now (Score:1, Funny)

    by Anonymous Coward
    Damn, now it's gonna be even harder to pass off my being late.

    GOD, those interuption adds are HUGE!!!
  • Duh! When this clock breaks the mercury will go everywhere! They already went through this phase with thermometers.

  • um (Score:1, Interesting)

    by mar1no ( 559482 )
    what exactly are they basing time on? what exactly is a second? and how is it that we determine its length?

    • Re:um (Score:2, Informative)

      by Metrollica ( 552191 )
      With a cesium-133 atom, a second is the time needed for the atom to perform 9,192,631,770 complete oscillations.

      • Re:um (Score:4, Informative)

        by esonik ( 222874 ) on Tuesday March 05, 2002 @07:23AM (#3111785)
        The above wording is imprecise. 9,192,631,770 Hz is the frequency of the electromagnetic wave that triggers a certain transition in a cesium-133 atom. So, what oscillates is not the complete atom, but the electric and magnetic field. Details can be found here [www.nrc.ca]

    • Re:um (Score:3, Insightful)

      by akiaki007 ( 148804 )
      We know how long a second is. Time as we measure it is based on Earth's rotation and revolution.

      What this measument is, is that it will not deteriorate over time as most methods of time measurement do currently. That is why it is so accurate. What that really means it that over time it will prove to be more accurate than anything else that we have created. A second will still be a second, and it's lenght will not change now.

      • Re:um (Score:1, Insightful)

        by Anonymous Coward
        "We know how long a second is. Time as we measure it is based on Earth's rotation and revolution. What this measument is, is that it will not deteriorate over time as most methods of time measurement do currently."

        Ya, it's completly accurate unless a butterfly flaps its wings in China and flys to another part China, thus changing the Earth's weight distribution and screwing up the Earth's rotational period. Even such a small change matters.

        Can you imagine the effect people,oceans, lithospheric plate movement, etc. have on the frequency of the events you say are stable and always predictable?

        • Re:um (Score:1, Informative)

          by Anonymous Coward
          Funny thing, today I was just reading the Java API documentation for the java.util.Date class, which has many good time related links, on in particular explaining why astronimical time measurements are not accurate enough, at least over shorter time periods.
      • Wait, so you're saying a second is defined in terms of the Earth's rotation? Because, that's not constant, especially in these million year durations that cesium clocks are supposed to only lose a few seconds through. I was under the impression that 'second' was defined in terms of our most precise measurement device, which, up until now, has been cesium:

        (taken from merriam-webster): "the base unit of time in the International System of Units that is equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom

        • Re:um (Score:4, Informative)

          by CentrX ( 50629 ) on Tuesday March 05, 2002 @04:58PM (#3114515)
          Originally, the second was defined to be 1/86,400 of the mean solar day. Because this is inaccurate due to irregularities in the Earth's rotation, that is the length of the second would change, finer standards were chosen. These finer standards are based on the original standard, but because they are defined in another way, they will not change unless the fundamental properties of the universe do.

      • Re:um (Score:2, Interesting)

        by JohnPM ( 163131 )
        We know how long a second is. Time as we measure it is based on Earth's rotation and revolution.

        Nah we stopped doing that a long time ago. The revolution of the Earth is slowing down as the Earth sheds angular momentum to the moon. There are other relatively minor effects on the rate of the Earth's rotation. One of the ways we measure change in astronomical periods is by using incredibly accurate atomic clocks.

        The original poster had a very good question: How do we define the second with such accuracy. The answer is basically: arbitrarily. In the end it doesn't matter as long as we all agree on a very accurate estimate.

        As an interesting side note, even the calender is not completely determined yet. Since the number of days in a year is not a round number we have a number of rules for ammending the calender. Everyone knows about the leap year every 4 years. But this rule is skipped on years divisible by 100. The second rule is skipped on years divisible by 400. Even these adjustments are not sufficient and the interesting bit is that IIRC, noone has decided on how to handle additional corrections. The current drift rate is around 1 day in 3300 years, so if you want to book that venue for your 5000 birthday now, it will be difficult to get the date right.
        • Am I correct in assuming the following?

          A second or an hour is arbitrary as mentioned and has no natural counterpart.

          A year is a natural occurence that is composed of the arbitrary seconds and hours. Since the natural year is not constant and our arbitrary seconds are, the local time has to be adjusted to agree with the natural movement of earth around sun.

          Question is: is it possible to build a clock that will have a perfectly variable second? I think the answer is no because we can't predict what the change in the physical interplays of the planets will do. Is that correct?

    • One second is "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom." (http://physics.nist.gov/cuu/Units/current.html [nist.gov])
    • The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

      according to the National Institute of Standarts and Technology [nist.gov].

      so we know it by definition, which is pretty accurate. it has to be, our definition of a meter depends on it.
      but you wouldn't believe how a kilogram is defined...

  • Now we need a whole new... (Score:3, Funny)

    by itwerx ( 165526 ) on Monday March 04, 2002 @11:34PM (#3110543) Homepage
    ...nursery rhyme to replace Hickory Dickory Dock:

    Flappity floppity flip,
    A mouse on a moebius strip,
    The strip revolved,
    The mouse dissolved,
    In a chronodimensional skip!

    :)

  • Go down and take a tour! (Score:3, Informative)

    by hound3000 ( 238628 ) on Monday March 04, 2002 @11:37PM (#3110555) Journal
    The NIST labs out in Boulder, CO is a fabulous place to go and visit if you ever find yourself in town, or in Denver. They will gladly take you on a tour, and show you all sorts of interesting toys that they have. Probably the best part of the tour for me was the liquid hydrogen. Even better was touching it. Yes I did, yes I still have all my digits. Basically, it is exactly the same concept as fire; move your hand thru it very quickly. In this case, touch it quickly and retract. The tour guide also shrank a balloon completely down, as we all watched, as it slowly got bigger when he took it back out. And of course on the tour, was getting to see the atomic clock. (On the other side of a window of course.) Check it out!

    And if you are in Boulder, and enjoy tea, make sure to take a tour of the Celestial Seasonings Tea Plant. If you have sinus problems, their Peppermint room will take care it, pronto.

  • Hmm.... (Score:5, Interesting)

    by rtaylor ( 70602 ) on Monday March 04, 2002 @11:41PM (#3110575) Homepage
    I've always wondered just how they determine how reliable a clock is.

    Afterall, can't measure meters without a meterstick. Do they simply take a N Cesium clocks and average out their time to determine how close a single Mercury based clock sticks to it? Or did I miss the memo where we could acurrately time trillionths of a second?

    • Re:Hmm.... (Score:5, Informative)

      by norton_I ( 64015 ) <hobbes@utrek.dhs.org> on Tuesday March 05, 2002 @12:10AM (#3110698)
      Basically, the accuracy of a reference clock in principle determined by making two identical clocks, starting them synchronized, and measuring how long before they drift by an average of 1 second.

      This has to do with how cold your atomic fountain is, and how well you isolate the particular magnetic sublevel you define the second in terms of.

      Now, if you want to move to a mercury standard clock, you can do two things: first, calculate with QED the ratio of the freqencies between the transitions in cesium and mecury of interest. I don't know if we can do this well enough for these purposes or not. Second, you can redefine the second in terms of the oscillation frequency of some mercury transition at least within the accuracy of a current cesium clock.

      The important thing to note is that mand physicists don't really care about how long a second is, as much as they care that two clocks run at the same rate, even if it is wrong.
    • A meter is a certain exact fraction of some property of earth, obviously having to do with the size in some way. There is a stick of iridium in Europe somewhere that is exactly the length of a meter, and it is on this that all meter-sticks are based.

      Sorry about the lack of real, useful information, perhaps someone else has the numbers?

      • Re:Hmm.... (Score:2, Informative)

        by MrNixon ( 28945 )

        Actually, the meter is now defined as the distance light travels in vacuum during 1/299 792 458 of a second. This happened in 1983. Originally, it was 1 / 10 000 000 the distance between a pole and the equator, but that was way back in 1793.

        Check this link [colostate.edu] for more details.

      • A meter is defined by the General Conference on Weights and Measures [www.bipm.fr] to be the distance light travels in a vacuum in a time interval of 1/299,792,458 of a second. The 1889 definition of the meter was based on an international prototype of platinum-iridium.
    • Comment removed based on user account deletion
  • ...now more accurate than time itself. In a press release Time said that with advent of the new clock, it was no longer required, and was considering retiring to Whyoming for some well deserved self-off. When asked how it would occupy itself, Time suggested it might take up Fly fishing. Time said the flies reminded it of Fruit Flies, whose affinity for Bannanas was a constant source of amusement for Time over the years.
  • From what I remember from my college Physics/Relativity course [info gathered when I wasn't using the class as purely nap-time]: "time is relative". Isn't building a "perfect clock" impossible to do on Earth? In order for it to be accurate, wouldn't you have to create it somewhere in deep-space (ie. no large mass ANYWHERE affecting it) and somewhere where it would have absolutely NO movement (ie. not revolving around a star, not revolving around [the center of] a galaxy, not approaching anything that might be out there between the galaxies, etc...)?

    Just curious.

    • Re:relativity? (Score:2, Insightful)

      by Anonymous Coward
      "time is relative". Isn't building a "perfect clock" impossible to do on Earth?
      Yes, time is relative. What a clock does is measure the flow of time where the clock is. And it is accurate in doing it. If you need to measure a time interval for an experiment you're doing in your basement, the best thing is to have an atomic clock in your basement too.

      In order for it to be accurate, wouldn't you have to create it somewhere in deep-space
      Then you'll be measuring the flow of time in deep-space, which would be more accurate for a deep-space experiment, but less accurate for your basement experiment here on Earth.

      So the best thing is to have clocks where you need them, and maybe monitor the differences between them for fun. For example, because Boulder is about 1 mile above the sea level, the atomic clock there goes slightly faster than the Washington clock.

      Your suggestion of a clock in space would be a good way to define a universal time, but not a good way to gain accuracy.
      • there is no "universal time"

        That was one of the major points of relativity. There's no true state of rest either, incidentally. Flow of time and rates of motion are both relative. You can say two objects are stationary relative to each other, but that doesn't mean they both aren't moving. Time works similarly, since the difference in the rate of time flow on two objects is dependent on their relative velocities.

  • How do they count the ticks? (Score:4, Informative)

    by mmontour ( 2208 ) <mail@mmontour.net> on Tuesday March 05, 2002 @04:38PM (#3114360)
    One advantage of the new clock is that it ticks much faster. Today?s international time and frequency standards, such as NIST-F1, measure an atomic resonance of about 9 billion cycles per second. By contrast, the new NIST device monitors an optical frequency more than 100,000 times higher or about 1 quadrillion (US) cycles per second.

    A 9 GHz oscillation can be hooked up directly to electronic circuits, counters, PLLs, etc. My first question when I read this article was, how the heck do you synchronize anything else to a "frequency" that's in the optical / ultraviolet range? I found some more information on this page [nist.gov] and this one [nist.gov], so I guess that's how this new clock works.

  • A second? (Score:2, Funny)

    by bobdole369 ( 267463 )
    I always thought a second was saying "one one-thousand" or "one Mississippi" (gotta say it quick) or "One potato". at least thats how it was back when I played 2-hand touch football. You could only blitz when you counted to five or ten using one of the above accepted methods of timing a second. But for real now, why do we need to get that much better than a bloody cesium clock? Does somebody REALLY care whether it was 9.433324545 seconds or 9.433324549 seconds? Maybe scientists? Physicists? Psychotic deranged people who wear aluminum foil body suits and 14 swatches? Enlighten me people...

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