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New Atomic Clock Reaches the Boundaries of Timekeeping

Posted by Soulskill on from the reaching-the-level-cap dept.

SonicSpike sends an article from NPR about a high-tech clock being built at the University of Colorado Boulder. It's more precise than any clock before, able to keep perfect time for five billion years. "At the heart of this new clock is the element strontium. Inside a small chamber, the strontium atoms are suspended in a lattice of crisscrossing laser beams. Researchers then give them a little ping, like ringing a bell. The strontium vibrates at an incredibly fast frequency. It's a natural atomic metronome ticking out teeny, teeny fractions of a second." But this precision leads to a problem: the relativistic differences between keeping the clock on the floor versus hanging it on the wall now introduce more significant fluctuations than the clock itself. "Tiny shifts in the earth's crust can throw it off, even when it's sitting still. Even if two of them are synchronized, their different rates of ticking mean they will soon be out of synch. They will never agree. The world's current time is coordinated between atomic clocks all over the planet. But that can't happen with the new one."

7 of 249 comments (clear)

  1. Old saying by plover · · Score: 5, Insightful

    A man with one watch always knows what time it is.
    A man with two watches is never sure.

    --
    John
    1. Re:Old saying by lgw · · Score: 5, Insightful

      A further problem with hyper-accurate clocks is relativity. TFS mentions the issues with general relativity - strength of gravity affects timekeeping. But there's a more profound issue once you get crazy-precise: only co-moving clocks can be synchronized in the first place. The concept of synchronization simply doesn't apply to clocks moving at different velocities - and two clocks at different positions on the rotating, orbiting Earth will never quite be moving with the same velocity. That relativistic effect is tiny, but it's not even hypothetically reconcilable: there are only so many significant digits of time possible to share between clocks in different locations.

      --
      Socialism: a lie told by totalitarians and believed by fools.
    2. Re: Old saying by Anonymous Coward · · Score: 3, Insightful

      Sorry, that doesn't make sense. It's a 4D problem because you don't know what time it is. Three spheres intersect at a point, but there are still multiple possibilities because you don't know how big the spheres are.

    3. Re: Old saying by Altrag · · Score: 1, Insightful

      Yes but you can perform a transformation to translate from one reference frame to another, and while the universe may not give special meaning to any particular reference frame, there's nothing stopping us from doing so. So in theory you can define a "universal" time if you want.

      Similar to choosing where to place the origin on a sheet of graph paper. It doesn't really matter where you put it (mathematically at least) but once its there you have a perfectly meaningful "universal" point of reference to use when describing the positions of other objects.

      The trouble of course is computing the transformation parameters with enough accuracy to matter, which I'm assuming is implausible on our not-mathematically-perfect planet.

    4. Re:Old saying by nabsltd · · Score: 3, Insightful

      You need a 4th one for the time. Without an accurate time reference, you can't determine distance to satellites.

      Every GPS signal is the time...that's how it works.

      The signal from different satellites (which includes the time, the satellite ID, and the satellite position) is enough by itself to give you everything you need, and by determining how long each signal took to reach the receiver, the position can be fixed.

      You only need 3 satellites if your position is already generally known (i.e., what hemisphere), or if the receiver assumes you are reasonably close to sea level. With 4 satellites, you can get a fix with no previous knowledge of where you were. Four will also give you accurate altitude after a few iterations.

  2. They finally invented a clock so accurate... by unitron · · Score: 5, Insightful

    ...that it can't be used to tell time reliably.

    --

    I see even classic Slashdot is now pretty much unusable on dial up anymore.

  3. Re:...and also not true by Bengie · · Score: 5, Insightful

    Since "perfect" is impossible, making it a useless word, lets just redefine it to something useful, like the colloquial usage of "close enough with respect to the current standard margin of error.