‘Time is elastic’: Why time passes faster atop a mountain than at sea level

Time moves slower the closer you are to Earth. In his theory of general relativity, Einstein explained that the gravity of a large mass, like Earth, distorts the space and time around it.

In 2010, researchers placed two precise atomic clocks, one 33 centimetres higher than the other. Time moved slower for the clock closer to Earth. This confirmed that absolute time does not exist.

If one looks at reality on the smallest scale, using equations of quantum gravity, time vanishes. However, we still perceive time as moving forward sequentially.

Key aspects of time are described by the second law of thermodynamics, which states that heat always passes from hot to cold. Ice cubes melt in hot water, never in reverse. A similar phenomenon might explain why we can only perceive the past, not the future.