your head is older than your feet, and now it's even older

[eub]

http://www.sciencenews.org/articles/20060422/bob8.asp

Every decade since the mid-1950s, the accuracy of atomic clocks has improved tenfold, notes Kleppner. The clocks are approaching an accuracy of 1 part in 10¹⁶, and newer systems, based on the vibrations of laser-cooled atoms and ions, are expected to eventually attain 1 part in 10¹⁸.
[...]
Given the current accuracy of clocks, this gravitational effect requires that researchers know the altitude of timekeeping laboratories to within a few meters. Ultimately, altitudes would have to be measured to within a centimeter.

That becomes tricky because gravitational theory dictates that the altitude isn't measured relative to average sea level, but to the geoid, a hypothetical surface that approximates the shape and size of Earth. The geoid's size fluctuates in response to, for example, ocean tides and the redistribution of water due to climate changes.

This is impressive.

Comments

[bhudson.livejournal.com]

So clock people have a Moore's Law of their own? Freaky.