The true nature of Albert Einstein's theory that time is a relative concept and the higher you live above sea level, the faster you should age, has been demonstrated with the world's most accurate clock for the first time.
Experts found that time really does run more quickly the higher you are - just as Einstein predicted, The Independent reported Tuesday.
They monitored two atomic clocks positioned just a foot apart in height above sea level.
Einstein had proposed 100 years ago in his theory of relativity that time and space are not as constant as everyday life would suggest.
He suggested that the only true constant, the speed of light, meant that time can run faster or slower depending on how high you are, and how fast you are travelling.
James Chin-Wen Chou and his colleagues from the US National Institute of Standards and Technology in Boulder, Colorado, conducted the study.
"These precise clocks reveal the effects of gravitational pull, so if we position one clock closer to a planet, you also increase the gravitational pull and time actually runs slower than for another, similar clock positioned higher up," Chou said.
"No one has seen such effects before with clocks which is why we wanted to see if these effects are there. We would say our results agree with Einstein's theory - we weren't expecting any discrepancies and we didn't find any," the newspaper quoted him as saying.