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Keeping Time with a Mercury Atom 153

Roland Piquepaille writes "The National Institute of Standards and Technology (NIST) has announced that a new experimental atomic clock based on a single mercury atom is now at least five times more precise than NIST-F1, the U.S. standard clock. This mercury atomic clock 'would neither gain nor lose a second in about 400 million years' while it would take 'only' 70 million years to NIST-F1, based on a 'fountain' of cesium atoms, to gain or lose a second. But even if this new kind of optical atomic clock is more accurate than cesium microwave clocks, it will take a while before such a design can be accepted as an international standard. A ZDNet summary contains pictures and more details about the world's most precise clock."
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Keeping Time with a Mercury Atom

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  • by enrevanche ( 953125 ) on Sunday July 16, 2006 @02:43AM (#15727090)
    i'm sure that they use a stable isotope.

    the isotope you mention (194) is synthetic anyways

  • by gardyloo ( 512791 ) on Sunday July 16, 2006 @02:53AM (#15727108)
  • Re:400 million years (Score:5, Informative)

    by evilviper ( 135110 ) on Sunday July 16, 2006 @04:14AM (#15727248) Journal
    Only test that I can think of would be to build two of these, plus a control of some sort, and leave them right next to each other for ten years. Only the control will be less accurate than the device you're measuring...

    The same way they've been doing it for many years with current atomic clocks... You don't just have a single clock, you have a BANK of numerous atomic clocks, and use statistical sampling to correct drift. And establish a very, very accturate time base.
  • by oskay ( 932940 ) on Sunday July 16, 2006 @04:53AM (#15727322) Homepage
    The 400-million year figure is still limited by technical issues, not fundamental physics. It is expected that once a few more calibration methods are tried out, that it will be able to reach its theoretical limit, which actually does turn out to be pretty close to one second in five billion years. In any case, these millions-of-years figures are not really practical-- they're just the way that clock people phrase things so that they sound good in the popular press. What really matters is that the precision that can be obtained in a much shorter period of time is much higher. Right now the mercury clock has errors at the level of about a second in 400 million years-- but a second is a lot of timing error! Perhaps a more useful (but equivalent) figure would be 2.3 ns per year, or perhaps you would rather use 44 picoseconds per week.
  • by oskay ( 932940 ) on Sunday July 16, 2006 @05:33AM (#15727377) Homepage
    The trick is that the second is defined to be the frequency of an unperturbed cesium atom, which is about as real as that "frictionless plane" that you might have had in high-school physics.

    An example of the problem is this: for technical reasons, a small magnetic field is needed inside a cesium clock. Magnetic fields change the spacing between all atomic energy levels to some degree. For cesium, the relevant change is very small, but it is still there. What you need to do is measure the magnetic field, calculate how much it affects the frequency of the atomic transition, and correct your output frequency by the required amount. What ultimately sets the accuracy level of a given clock is how well the magnetic field shift (and dozens of others) can be corrected for.

    The same is true for the mercury clock. The difference is that the systematic frequency shifts that can affect accuracy of the clock are now understood, and controllable, at a higher level of precision.

  • Re:Why? (Score:3, Informative)

    by bmo ( 77928 ) on Sunday July 16, 2006 @07:08AM (#15727498)
    Like the other guy said, radar, lidar, but also add navigation and land surveying. Longitude is determined by time difference between UTC and local time. If you make this clock small enough, and replace the current constellation of GPS satellites with new ones based on this type of clock, you increase the resolution.

  • Re:Missing the point (Score:3, Informative)

    by Teancum ( 67324 ) <robert_horning AT netzero DOT net> on Sunday July 16, 2006 @09:06AM (#15727703) Homepage Journal
    To add a more practical real world example to this line of thought....

    Clock accuracy is one of the key components of GPS systems and other navigational equipment. By having a much more accurate clock, you would be able to build devices that can determine with higher precision exactly where you are on the Earth... or for that matter in space even.

    If you aren't aware of the "data" that is streamed out of GPS satellites, all that is transmitted is a clock signal that simply says what time it is right now, and along with some identification information. When compared to other satellites and applying some fairly straight-forward mathmatics (that includes some relativity equations), you get your current position.

    In fact, while you might be able to determine within about 20 feet where you are at with current GPS technology and think that is "good enough" for the purposes of using that technology, navigation in the Solar System is going to need even higher clock accuracy in order to plot accurate trajectories to Mars and not get the current 30% failure rate of spacecraft trying to get there and accidentally crashing into the surface or other navigational mistakes caused by inaccurate plotting of the motion of both Mars and the Earth.

    In short, you life someday (perhaps even now) might litterally depend on the navigation equipment of the vehicle you are in (read airliner) knowing precisely where you are at, and a more accurate clock will give that vehicle better accuracy to keep you alive.
  • Re:Closed Season (Score:3, Informative)

    by 1u3hr ( 530656 ) on Sunday July 16, 2006 @11:51AM (#15728176)
    How is his personal page any sleazier than ZDNet's summary?

    His blog IS what he describes as "ZDNet's summary". The same link he spams in every one of his submissions.

  • Re:400 million years (Score:3, Informative)

    by ceoyoyo ( 59147 ) on Sunday July 16, 2006 @12:41PM (#15728344)
    Having a very accurate clock can let you do all kinds of interesting things. For example, if you find it easy to measure time VERY accurately, but difficult to measure very small distances (which we do) then you can set up experiments where time is an indirect measure of distance (as in, how long does it take this laser beam to travel there and back?).

In seeking the unattainable, simplicity only gets in the way. -- Epigrams in Programming, ACM SIGPLAN Sept. 1982