Even more precise ytterbium-based atomic clocks


VIP/Donor & WBF Founding Member
May 6, 2010
Boston, MA

The most recent record-breaker, released last year, was so precise it would could keep time without losing or gaining a second for 15 billion years.

And the standard second is defined by the oscillations of a caesium atom. So, you know, pretty amazingly precise stuff.

So what do these new records mean?

Systematic uncertainty refers to whether the clock is accurately keeping time with the oscillations of the atoms. The two clocks were in sync with the frequency of the ytterbium with an error rate of 1.4 parts in 10^-18.

Stability refers to the change in the clock's frequency over a specific time period. The ytterbium clocks' change was just 3.2 parts in 10^-19 (or 0.00000000000000000032).

And finally, reproducibility refers to how closely the clocks tick at the same frequency. Their difference was below the level of 10^-18, or a billionth of a billion. And this is the money shot.

"The agreement of the two clocks at this unprecedented level, which we call reproducibility, is perhaps the single most important result, because it essentially requires and substantiates the other two results,"
Atomic clocks have also been used to detect and measure time dilation, the effect of velocity or gravity on time. Relative velocity slows time. Greater gravity also slows time; for example, at higher altitudes on Earth time actually moves a wee bit faster.

Because of this difference, atomic clocks can be placed at different altitudes to measure gravity itself. This means these new clocks could - theoretically - be used to measure the shape of Earth's gravitational field, a field known as relativistic geodesy, to within an accuracy of a centimetre.
[As of 2010]
Now, physicists at the National Institute of Standards and Technology (NIST) have measured this effect at a more down-to-earth scale of 33 centimeters, or about 1 foot, demonstrating, for instance, that you age faster when you stand a couple of steps higher on a staircase.

Described in the Sept. 24 issue of Science,* the difference is much too small for humans to perceive directly—adding up to approximately 90 billionths of a second over a 79-year lifetime—but may provide practical applications in geophysics and other fields.

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