Time Out of Joint

O’Brian oversees America’s master clock. It’s one of the most accurate clocks on the planet: an atomic clock that uses oscillations in the element cesium to count out 0.0000000000000001 second at a time. If the clock had been started 300 million years ago, before the age of dinosaurs began, it would still be keeping time — down to the second. […]
At the nearby University of Colorado Boulder is a clock even more precise than the one O’Brian watches over. […] This new clock can keep perfect time for 5 billion years.”It’s about the whole, entire age of the earth,” says Jun Ye, the scientist here at JILA who built this clock. […]
But this new clock has run into a big problem: This thing we call time doesn’t tick at the same rate everywhere in the universe. Or even on our planet.
Right now, on the top of Mount Everest, time is passing just a little bit faster than it is in Death Valley. That’s because speed at which time passes depends on the strength of gravity. Einstein himself discovered this dependence as part of his theory of relativity, and it is a very real effect.
The relative nature of time isn’t just something seen in the extreme. If you take a clock off the floor, and hang it on the wall, Ye says, “the time will speed up by about one part in 10¹⁶.” […] Time itself is flowing more quickly on the wall than on the floor. These differences didn’t really matter until now. But this new clock is so sensitive, little changes in height throw it way off. Lift it just a couple of centimeters, Ye says, “and you will start to see that difference.” […]
The world’s current time is coordinated between atomic clocks all over the planet. But that can’t happen with the new one.