Space-time is a mathematical and physical construct that explains how space and time interact; the three physical dimensions and one time dimension combine to create the four-dimensional nature of the universe. Space-time resulted from Albert Einstein's work on relativity.
Relativity states that objects moving through space at different speeds experience time differently, and experiments have provided support for this notion. This poses problems for high-speed space transportation, as people on a spacecraft traveling near the speed of light would experience time far more slowly than people on Earth. This time difference is measurable, even within a planet-sized space. The time kept on GPS satellites, for example, drifts when compared to clocks on Earth, and they need to be adjusted regularly.