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Keeping Time with a Mercury Atom 153

Posted by Zonk
from the nice-watch dept.
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 legallyillegal (889865) <legallyillegal@@@gmail...com> on Sunday July 16, 2006 @01:19AM (#15727035) Homepage
    syncing to time.singlemercuryatom.nist.gov doesn't work yet.
  • 400 million years (Score:2, Insightful)

    by gfody (514448)
    It's easy to make impressive statements like that when you know nobody will be around to prove you wrong!
    • by gardyloo (512791) on Sunday July 16, 2006 @01:28AM (#15727054)
      Pfft. You'll regret saying that when the readers of the future see the article's 3.56*10^12th dupe.
    • by evilviper (135110) on Sunday July 16, 2006 @02:02AM (#15727123) Journal
      It's easy to make impressive statements like that when you know nobody will be around to prove you wrong!

      Complete nonsense. This isn't a "prediction", it's a mathematical number/time. Like any other number/time, you can easily convert it into shorter time-frames.

      1 sec in 400 million years is ==
          1/2 sec in 200 million years
          1/4 sec in 100 million years
          1/8 sec in 50 million years
          etc.

      That means it is accurate to 0.000000025ths of a second in 10 years... A more partical time-frame, which can be tested fairly easily.
      • That means it is accurate to 0.000000025ths of a second in 10 years... A more partical time-frame, which can be tested fairly easily.

        How, exactly?

        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...
        • Re:400 million years (Score:5, Informative)

          by evilviper (135110) on Sunday July 16, 2006 @03:14AM (#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.
    • What matters is that it's a clock with a 10^-16 s precision. Now I'm not sure how quantum physics needs that much precision.
      • Re:400 million years (Score:3, Informative)

        by ceoyoyo (59147)
        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?).
    • by Das Modell (969371) on Sunday July 16, 2006 @05:42AM (#15727453)
      It's easy to make impressive statements like that when you know nobody will be around to prove you wrong!

      This man [wikipedia.org] begs to differ.
    • 1 second in 400 million years is an impressive number for the journalists. What they really mean is that (I am assuming here that clock drift behaves like a random walk function) that the clock is expected to drift by less than 15 microseconds per month.
  • by GreggBz (777373) on Sunday July 16, 2006 @01:30AM (#15727059) Homepage
    Great news for those mission critical D-Link routers! [slashdot.org]

  • by mrjb (547783) on Sunday July 16, 2006 @01:31AM (#15727063)
    They're treating time as if it were something absolute.
    • by Umbral Blot (737704) on Sunday July 16, 2006 @01:37AM (#15727077) Homepage
      Relativity doesn't make clocks less useful, in fact it makes them more useful (because you can use them to figure out how fast you are going as well). And assuming that the clock remains under constant acceleration there is no reason to believe that relativity would make it less accurate.
      • A clock in only accurate within its own space and time. For example, moving this clock to another area of the universe may slow or speed it up. However, say you are in the same area as this clock...would you notice the change in pace? No. The only way to measure change is against another point of reference such as another clock located in another part of the universe.

        Don't you just love relativity? ;) It's a topic which defines nothing being absolute.
        • I didn't say you could do it with a single clock. And it's "frame of reference" not "space and time" there are many frames of reference, and only one space-time.
      • by Lumpy (12016) on Sunday July 16, 2006 @07:39AM (#15727664) Homepage
        That an it will help prove my Theory that there is a black hole in time here on the planet earth. AS we age we accelerate towards the black hole and therefore experience time distortion. Think about it. As a child summer took F-O-R-E-V-E-R. As a Teen it took about what felt like the right amount of time. As a Young Adult in college it seems like summer was shorter than normal. A person in their 40's summer feels like about 3 weeks and other effects of time distortion take effect.... Week-ends feel like they last ony a single day. And the inconsistancies also start showing as the time gravitional waves pass by you. A work week seems like it took a day to pass while a co-worker next to you in the same age bracket feels like it took much longer.

        As you get near your 80's the gravity of the black hole starts tugging not only at your time harder by at you in physical ways. Your skin starts sagging, you break bones easier because of the greater gravity in the physical dimensions.. How many people have heard old people complain it's hard to walk?? Huh! Observable proof!

        Mercury clocks would help here. We attach one to every newborn for a decade and then look at the time distortion as it happens so we can figure out how to defeat this terror.

  • by tylernt (581794) on Sunday July 16, 2006 @01:34AM (#15727071)
    So... at what point do you say that a clock is accurate enough? I mean, yeah maybe this thing is more accurate than current technology, but if it turns out to be way more expensive, why bother? How often do you need the accuracy that current technology can't provide?
    • by gardyloo (512791) on Sunday July 16, 2006 @01:53AM (#15727108)
    • I was surprised it took the "why bother?" people this long to flourish out of the woodwork. I'm no physicist, but if it was pointless they wouldn't do it or it'd be some poorly-funded "just because" research project in a closet somewhere. See my sig for further details.
    • We can always use more accuracy. Many communications systems rely on accurate clocks to keep the transmitters and receivers in synchronization. Frequency stability is also important for communications systems and test and measurement equipment. Any defects in the clock will degrade the performance of the equipment.
      • Having accurate clocks on this scale isn't useful for synchronization, because there's more inaccuracy in distribution of the clock signal from the accurate clock to the transceiver, and more variability in the latency of the transmission than there is error in a standard atomic clock. Consider that modern communications within computers off-chip (and sometime on-chip) are asynchronous (the transmission is sampled to determine the bit synchronization, rather than the ends simply expecting to agree or have a
        • Think about direct sequence spread spectrum systems that use cryptographically secure spreading codes. The PN code generator in the receiver must be synchronized with the PN code generator in the transmitter for the receiver to be able to despread and detect a transmitted signal. There are also navigation systems that are designed on the assumption that the user has a very accurate local clock. A clock driven by a high quality cesium beam frequency standard can easily gain or lose a nanosecond per day. That
    • The real point of the improvement isn't to give longer stability; it's that you can measure smaller units of time accurately with the new clock. A standard commercial cesium clock produces a clock signal at 5 MHz (and at 1 Hz), both extremely accurately. This is because, while the device is measuring an exactly 9.192631770 GHz frequency, this measurement can't just increase a counter each time; what it does is stabilize a quartz crystal oscillator, such that there is extremely little accumulating drift.

      The
    • So... at what point do you say that a clock is accurate enough?

      When you can snipe anybody at will on eBay. [slashdot.org]

  • Why? (Score:2, Interesting)

    by mh101 (620659)
    Can someone explain why we even need this sort of precision?

    • Scientific experiments, etc. etc.
    • Obligatory: Me Too!

      What's the practical application for something like this? Is this a "win" in the science category, or is this just another way of doing the same thing?
      • What's the practical application for something like this?
        Radar and lidar. The more accurate the instrument's clock, the more accurate its distance measurements.

        Also, gravity affects time, so you can use clocks and radios to measure the relative gravitational potential between two points in space. By sending a sufficiently good clock into deep space, we might be able to see if the solar system contains any dark matter.

      • Re:Why? (Score:3, Informative)

        by bmo (77928)
        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.

        --
        BMO
    • If we forget the length of a meter we can use that clock to measure the speed of light accurately enough to know how large a 299792458th of the distance it travels per second is?
      • by jZnat (793348) *
        That's true; we can measure how far light travels in a certain time more accurately than the converse.
  • While a 70 million to 400 million jump is quite exceptional, how long will this continue? Will anyone really want to use a clock that won't lose a second until AFTER the sun has expanded and burnt up the earth (~5 billion years)?
    • by rwwh (989154) on Sunday July 16, 2006 @03:40AM (#15727291) Homepage
      Scientific American once had a nice paper about time. I remember these two facts:
      • At an accuracy of 10^-17, the earths gravity makes that two identical clocks, one of which is 5cm higher up than the other one, will start deviating from each other (i.e. time really IS different 5 cm up, at this accuracy)
      • At an accuracy for 10^-17, relativistic effects start playing a role at walking speeds (i.e. time really IS different at walking speed than at rest, at this accuracy).
      I think 5cm and 5km/hour are reasonable usability limits, hence an accuracy of better than 1:10^17 would not make much sense to me.
      • I think 5cm and 5km/hour are reasonable usability limits, hence an accuracy of better than 1:10^17 would not make much sense to me.

        There's always applications that will need better accuracy. It's not wise to draw the line here. Most of the human race probably could live with a clock that loses an hour every week.
    • 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 precis
  • Why is it that cars break in 15 years, and most other things are extremely fragile, but this clock can last 40 billion years? Is it made from some kind of super-dense material? Why is the quality of this timepiece so great, and how is it made? It would be nice to have some technical information on how an ordinary person could manufacture a timepiece of this exact precision. Are the materials from a very deep mine? Are they hydrogen materials? Why is this clock so accurate?
    • It would be nice to have some technical information on how an ordinary person could manufacture a timepiece of this exact precision. Are the materials from a very deep mine? Are they hydrogen materials? Why is this clock so accurate?

            *sob*
    • Actually, the logical design of the clock will last 40 billion years until it produces an error. I'm quite sure we will never design any sort of mechanical device can actually last that long to find out.

      //unless you socket it with a zod rune...
    • I do have an answer for you. Most things break in a specific time span because of lack of maintaince + abuse.

      There are many cars from the 60's, 70's, and 80's on the road now that look fantastic and work great. While I can point at about 5-6 around here that are less than 4 years old that are on their last leg. Cars specifically suffer from the "what? I change the oil and put gas in it" syndrome. Cars need around $400-$1000US in maintaince every year and they do not get it. Most cars on the road do not
  • by viking2000 (954894) on Sunday July 16, 2006 @01:56AM (#15727114)
    ...from the Heisenberg uncertainly principle:

    The more precisely
    the MOMENTUM is determined,
    the less precisely
    the POSITION is known

    So this clock is unfortunately missing. And when it is found, it is not so accurate anymore.
    • It gets worce than that. How long to you think it'll take for that single atom to tunnel out of there. How embaracing would that be: scientists are finally on the verge of proving string theory in a spectacular, multinational, high precision experament when:
      Scientist1 "Sir the clock stopped, we seem to have lost the atom."
      Scientist2 "Well look around, it has to be here somewhere."
    • I think the Heisenberg Uncertainty Principle also extends to other measurements such as force:time, inertia:time (if you derive that from position:momentum), etc.
  • 400 million years in the future, my descendents will profit unthinkable amounts from their ownership of y400002k.com

    Just in case the religious right get a further hold on our country in the future, I've also registered jesuswillreturn400002k.com and (hedging my bets) spaghettimonsterwillreturn400002k.com

    but we all know that by that time, humanity will simply be slaves to the powerfully accurate mercury clock.

    So, I for one welcome our new mercury atom overlords, and remind them that mercyatomoverlords.com ca
  • by tsa (15680)
    Teacher: What! You're 15 attoseconds late! Again! Go stand in the corner!
  • but will it (Score:2, Funny)

    by p51d007 (656414)
    Fit on my wrist??????????
  • by dtfinch (661405) *
    How do you calibrate a new atomic clock, if you have nothing more accurate to compare it against? And if we have clocks that won't lose or gain a second in 70 million years, why do we need to develop one that won't lose or gain a second in 400 million years?
    • by oskay (932940)
      Calibration is a process that evaluates the possible sources of frequency shifts, measuring how strong each type of stimulus and response is. For example, how strongly is the transition frequency affected by magnetic fields, and how much magnetic field is there?

      It's actually the same procedure that's already used for the best cesium clocks-- there's isn't (or wasn't anyway) anything better to compare those to, and yet they've been making great strides forward for fifty years now.

      As for the second questi

    • "How do you calibrate a new atomic clock, if you have nothing more accurate to compare it against?"

      A combination of the metric of fuckload of cesium clocks the world uses for official timekeeping and of known astronomical events. In other words, the same way we figure out UTC.

      "And if we have clocks that won't lose or gain a second in 70 million years, why do we need to develop one that won't lose or gain a second in 400 million years?"

      Because it takes 70 million years to lose an entire second. If, for exa
  • by stuffman64 (208233) <stuffman@NOsPAm.gmail.com> on Sunday July 16, 2006 @02:19AM (#15727155) Homepage
    I'm just curious about something here. If a second is defined to be 9,192,631,770 oscillations of a Caesium-133 atom, then why is it said atomic clocks are accurate to within a second over 70 million years? Isn't that lost/gained second itself defined by the Caesium atom's transitions? I hope this question makes sense...
    • by Anonymous Coward
      For any definition of a fundamental unit, there are (quantum-mechanical or practical) limitations on how accurately the specified measurement can be made. Thus, there is a small but finite spread in the effective values used by different laboratories. As long as the new standard is within that range, it is "exactly the same" in the sense of being indistinguishable, but nonetheless better, because its measurement uncertainty is smaller.

      Whenver the definition is revised, the new proposed standard is compare
    • Sure it does. You just need to realize that what they really mean is "a second is that unit of time that we can measure by counting 9,192,631,770 occilations of a Caesium-133 atom", with the emphasis on the WE.

      Let's take another absurdly re-defined measurement, the meter (you know, the basis of the entire metric system). It was originally defined, by the French Academy of Sciences, as one ten-millionths the distance from the north pole to the equator, in a line around the curve of the earth. The fact tha
    • Yes, you are missing something. The vibrations have to be counted, but this is not trivial. In fact, such clocks make use of a separate electronic oscillator and then try to keep it in sync with the atoms vibrations. Sometimes a cycle can be missed, offsetting the clock.
    • by oskay (932940) on Sunday July 16, 2006 @04:33AM (#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.

  • Upper Limit? (Score:2, Insightful)

    by NexFlamma (919608)
    At what point do people simply say that our time keeping methods are good enough?

    We already have a clock that only loses 1 second every 70 million years! The odds of the current time keeping system (or mankind, for that matter) continuing in it's current form for the next 70 million years are rather low, so why do we really need one that only loses a second every 400 million?

    Sure, it's nice to be able to improve, but can't the research money go to something more useful? Like, maybe cancer research or st
    • At what point do people simply say that our time keeping methods are good enough?

      Well, quantum theory says that there is in fact a smallest possible period of time, called Planck time.

      I assume that would be the limit. Not even the practical limit, but The Limit.

      --Eoban
      • Well, quantum theory says that there is in fact a smallest possible period of time, called Planck time.

        I assume that would be the limit. Not even the practical limit, but The Limit.


        Indeed, and as soon as a suitable thunderstorm comes past and Igor raises the lightning rod, we shall be able to measure it.

    • For timing things that take a lot less time than a second. Such as the interactions of elementary particles and stuff. Also, to triangulate across long distances with big angles (GPS). 400 million is a stupid way to explain it but what do you expect from the mainstream media.. Reallly, it's about higher precision. A "year" isn't really a definite unit of time anyway, because it is largely a human construct to explain the rotation of the earth. Unfortunately, the earth does not rotate at a constant vel
  • Accuracy (Score:2, Insightful)

    by thorndt (814642)
    I'm suspecting that this level of accuracy would be quite useful in high-end scientific experiements--not so much for general wall-clock settings.
    For example, measuring the duration of extremely short events--like in particle accelerators.
  • This reminds me of that one clock that someone wanted to stick into a New Mexico cave or something. It was big, mechanical (IIRC) and had a foot pedal that you stepped on to update the display.

    The details in my head are sketchy, but I think there was a Slashdot article on it. Maybe it wasn't. Anyway, this reminds me of it.
  • How do you determine that it will gain or lose a second in 400 million years instead of 70 million years if:

    A.)It hasn't been around long enough to find out.
    B.)There are no timepieces more accurate to base this estimate on.
  • wristwatch (Score:4, Funny)

    by elmartinos (228710) on Sunday July 16, 2006 @03:15AM (#15727251) Homepage
    Can't wait to have a wristwatch with this. My atomic wristwatch [leapsecond.com] is a bit too bulky.
  • The first picture in the ZDNet article is not actually of the mercury clock, it's of the strontium atomic clock under development at JILA. JILA is associated with NIST, but they are not even on the same campus. The strontium clock uses a competing technology and is at a much earlier stage of development-- and performance-- when compared to the mercury clock!

    Looks like Roland Piquepaille failed to RTFA?

  • I hear a lot of people asking why we need this much accuracy. I'll give you a hint, it's not so we'll know the time in 700 million years, it's so we'll know it now. Some years ago an expirament was carried out where an atomic clock was loaded on a plane and flown around for hours. When it landed again the clock on board was compared with a clock on land and the limit of the accuracy of clocks showed a difference predicted by relativity. Now imagine if we could add some decimal points to that difference, not
    • Re:Missing the point (Score:3, Informative)

      by Teancum (67324)
      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
  • Wait, so the White Rabbit is always in a hurry, but it's the Mad Hatter who has the accurate clock?
  • Daniel Kleppner of MIT contributed an article to Physics Today [physicstoday.org] which ruminated on the problems that clocks like this will have for international timekeeping. The trick is that the clocks will be able to see the diurnal variations in general relativistic gravitational potential. No two clocks like this on the surface of the earth will ever be able to agree with each other. A whole new set of computational protocols for combining their results into International Atomic Time (TAI) will be necessary.
  • Here's a brief article [nist.gov] (and a picture) of the US's current standard. There's also a graph showing that the US standard tends to be replaced roughly every 5-10 years.

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