Which phenomenon describes the increase in time intervals as observed from a stationary reference point compared to a moving observer?

Time dilation is a key concept in the theory of relativity, which describes how time intervals can appear to differ for observers in different frames of reference. Specifically, when an observer is moving at a significant fraction of the speed of light relative to a stationary observer, the moving observer's clock ticks more slowly compared to the stationary observer's clock. This means that time observed from the stationary perspective will seem to stretch or dilate, leading to longer recorded time intervals.

This phenomenon has been experimentally verified in various scenarios, such as in particle physics, where fast-moving particles exhibit longer lifetimes as seen from our frame of reference. It also plays a crucial role in understanding how GPS satellites, which move quickly compared to the surface of the Earth, require adjustments based on both special and general relativity to provide accurate positioning information.

The other options relate to different concepts: length contraction involves objects appearing shorter in the direction of motion to a stationary observer, relativity is the overarching framework that encompasses both these ideas and more, while space expansion refers to the increase in distance between cosmic structures in the universe over time and is not directly tied to the effects of relative motion on time measurement.