Time is affected by acceleration and gravity. Einstein’s theories of relativity predict that acceleration and gravity slow time and experiments that compare clocks on the Earth’s surface with those on spacecraft and satellites bear these predictions out in practice.
Now physicists have shown that the effects of these time-bending forces can be demonstrated in a single laboratory on Earth. The gravitational pull of an object increases the closer to its centre of mass, so an object on the Earth’s surface experiences a stronger gravitational pull than one at a higher altitude. Using ultra-accurate atomic clocks, physicists at the U.S. National Institute of Standards and Technology have compared the passing of time across small differences in height and acceleration. For instance, a clock lifted a foot above another ticks ever so slightly faster.
The effects are tiny, however, and too small to be picked up by humans.