Time moves faster at the top of a mountain than at sea level.

This phenomenon is known as gravitational time dilation and was first predicted by Albert Einstein in his General Theory of Relativity in 1915. Einstein proposed that massive objects like Earth curve the fabric of spacetime, which directly affects the passage of time. The closer an object is to a source of mass, the stronger the gravitational pull and the slower time flows relative to a distant observer.In 2010, physicists at the National Institute of Standards and Technology (NIST) in Colorado proved this using ultra-precise aluminum atomic clocks. They placed two clocks just 33 centimeters (about 1 foot) apart in height and observed that the higher clock ticked at a slightly faster rate. Over a 79-year lifetime, a person living at the top of a mountain would be about 90 billionths of a second older than someone at sea level.This effect is not just a theoretical curiosity but a critical factor in modern technology. Global Positioning System (GPS) satellites orbit approximately 20,200 kilometers above Earth, where gravity is much weaker. Because of this, their internal clocks gain about 45 microseconds per day compared to clocks on the ground. Engineers must constantly adjust these satellite clocks to ensure GPS locations remain accurate, as even a tiny error would cause navigation data to drift by kilometers every day.