Your gravity’s different than mine

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Gravity by color

There are new clocks coming out that keep time using lasers. I wrote about them here, but didn’t have room to tell of one of their more interesting abilities.

Optical atomic clocks, as they’re known, provide unique insight into some of physics’ most fundamental constants. Take the words of Dennis McCarthy, Director of Time at the U.S. Naval Observatory until 2005, who clarified that “the kinds of optical atomic clocks we now see around the world are no longer clocks. They’re gravity meters.”

Gravity is the weakest known physical force. It’s very difficult to measure precisely. It also interacts  faintly with the passage of time. New optical clocks are so sensitive as timekeepers that running two of them in parallel offset by a few centimeters in elevation allows scientists to measure gravity. Because one clock is closer to earth than the other, it will run slightly slower.

The field of geodesy will likely benefit. We’ll start to move the clocks around. Like migrating birds on magnetic trails, these little machines will tune into gravitational pull. They will scan earth’s density as they travel, they will transcribe the silent imbrication of shifting tectonics.

Will somebody drive atomic clocks on truck bed? Will that be a job of the future?

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