New Clock May End Time As We Know It : NPR
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."
The world's most precise atomic clock is a mess to look at. But it can tick for billions of years without losing a second. i
That is a sliver of a second. But this isn't some effect of gravity on the clock's machinery. 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."