Atomic Clocks So Accurate They Can Measure Gravity

By Bill Andrews | November 28, 2018 1:58 pm
atomic clock

An older version of an ultra-stable ytterbium lattice atomic clock at NIST. Ytterbium atoms are generated in an oven (large metal cylinder on the left) and sent to a vacuum chamber in the center of the photo to be manipulated and probed by lasers. Laser light is transported to the clock by five fibers (such as the yellow fiber in the lower center of the photo). (Credit: Burrus/NIST)

Time, like money, only seems important when it’s running out. But to physicists, time is always a big deal. Relativity tells us that the flow of time depends on the circumstances you’re measuring it in: Clocks tick faster on top of mountains than at ground level, for example, and the faster you go the slower your clocks go. Time depends on space.

But now, thanks to technological advancements in atomic clocks — the most accurate time-keeping devices we’ve devised — we can turn things around, and determine physical parameters more accurately by studying the passage of time. Our understanding of space will depend on time.

The new clocks, described today in the journal Nature, will also promise what better atomic clocks usually promise: improved timekeeping, communication and navigation technologies. But in addition to their insights into the physical space around them, the devices could also help find gravitational waves, test out predictions of relativity and hunt for dark matter. All that, just from super-accurate clocks.

Atomic Clocking In

This might all seem pretty complicated (and it is), so let’s start with the basics. As the paper’s authors helpfully put it, “The passage of time is tracked by counting oscillations of a frequency reference, such as Earth’s revolutions or swings of a pendulum. By referencing atomic transitions, frequency (and thus time) can be measured more precisely than any other physical quantity.” So, count how often specific atoms switch between energy levels, and you’ll get the most accurate ticks and tocks.

The foremost name in atomic clocks is the National Institute of Standards and Technology (NIST), and that’s where today’s research comes from. The latest clocks rely on 1,000 atoms of ytterbium, cooled to near absolute zero, trapped within 1-D grids (ie, columns) made of laser beams. By all the measures of atomic clock performance — minimizing errors of the atomic frequencies, ensuring the ticks are stable, and its results are reproducible — the NIST researchers produced, just, unbelievably precise clocks. Their error bars are on the order of 10-18, or a billionth of a billionth.

The Shape of Things

In fact, these atomic clocks are so accurate, they’re actually sensitive to gravitational influences. Normally, the relativistic quirks of gravity that tweak the flow of time are too minute for us to notice — but not anymore. As the authors put it, “If these clocks were compared across a long baseline or used for remote comparisons with other clocks around the world, the measurement would be limited by gravitational knowledge on Earth’s surface.” That is, they’re so accurate that the only thing that could alter their ticks and tocks would be gravity itself. Clocks higher up, farther from Earth’s mass, would tick faster than clocks lower down, thanks to relativity.

This is a major deal for the science of geodesy, which measures Earth’s shape and gravitational influence. Our current picture of the planet’s precise surface depends on satellites and computer modeling, which provide pretty good resolution, down to a few centimeters. But these atomic clocks would bring that resolution way down, to just one centimeter. Armed with two of these clocks, researchers could compare sea level on two different continents, the precise height of a mountain, or any other height-based (and, thus, gravity-based) measurement they care to make.

And because the atomic clocks are so sensitive to gravity, they can serve as a kind of detector for any related activity. Gravitational waves, as they pass through us and this planet, would show up in these clocks’ readouts. Extremely subtle experimental tests of Einstein’s theories are now possible, as well. And most tantalizingly, the technology could help detect minute quantities of dark matter, the invisible stuff that only interacts with gravity, and makes up the bulk of the universe’s matter.

To be clear, these are still merely possibilities. The authors have only just built these atomic clocks and shown how accurate they are. But, now that they know the technology works this well, a new future of physics discoveries might just be upon us. It’s about time.

MORE ABOUT: physics
  • Whothehell Cares

    Okay, so clocks higher up a mountain tick faster than clocks at sea level due to earths mass ? Wouldn’t that be offset by the fact that the linear velocity of a clock on the top of a mountain would be greater than a clock at sea level?

    • Ed Ardzinski

      This describes a physical change in how fast a reference oscillates, such as the ytterbium atoms.

      In the higher elevation clock the atoms will have vibrated more times over a kilometer than the lower elevation clock regardless of linear speed.

  • Thomas Dylan

    Why aren’t these idiots working of something useful?

    • UtahTwisted

      …says the idiot using the internet…

      • Thomas Dylan

        have you looked in the mirror “idiot using the internet…”

    • rubiks6

      Why are you reading news instead of playing Grand Theft Auto?

    • Kamran Rowshandel

      “Why aren’t these idiots working of something useful?”
      Bedouins and Hebrews instated eye-for-an-eye judicial policies and we can’t untangle ourselves without risking our lives for them in war and getting nuked at the same time.

      More South Africans than Hebrews died during the propaganda war.

      How possibly you can demand them to do something intelligent is beyond me. Dumbness, erasure of family records, erasure of history, erasure of literature, dissemination of propaganda, and assertion of Semitic superiority has been at the forefront of our specie’s ambition since Hammurabi first instated eye-for-an-eye policies.

      Yes, you can open the New Testament in Word and replace “Jesus” with “The Defendant” and see it is only a testimony in a legal case spread by the media just like OJ’s.

      The quirk is- every defendant in the enforcement of an eye-for-an-eye policy is basically the same guy that book is about.

      No, it’s not that “cool”, but it’s the facts.

      That’s why they call me The Kid

  • Laszlo G Meszaros

    How long and why do we want to mislead people with this “relativity” trash?

    • UtahTwisted

      …says the idiot using gps on his phone and the internet, which only works when compensating for the effects of relativity…

      • Laszlo G Meszaros

        Idiot, who believes this. Please, check the accuracy of a GPS device, then start calculating…
        Idiot, who thinks that time can pass differently for two observers.

        • UtahTwisted

          it’s really sad that you are so ignorant (or mentally ill) to not understand these things – or – alternatively just to admit that you don’t know and remain silent on such topics.

    • Matt

      How are you this stupid, in this day and age?

      • Laszlo G Meszaros

        1. Stupid, who knows nothing about GPS, but refers to it in an argument. Advice: check the accuracy of GPS, then start calculating.
        2. Please, also see above…

        • Matt

          I never said anything about GPS, I just called you an idiot. Which you are, if you can’t comprehend something as simple as time dilation due to gravity, something that’s been proven by thousands of experiments and observations for close to 100 years, and that modern technology relies on to even function. Seriously, read a damn book.

    • Uncle Al

      1) GPS and its on-board atomic clicks
      2) idiot

      • Laszlo G Meszaros

        Idiot? Read the above reply.

    • rrocklin

      I thought this was satire at first.

  • Uncle Al

    Now, the fun part! Time keeping varies as the moon quadrupole moment deforms the Earth (tides). Watering the grass outside will have the clock running slow. Clock rate will depend on latitude. This will be fun.

    the technology could help detect minute quantities of dark matter and a bountiful deep well of BS.


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