Spacetime is a mathematical model that integrates three-dimensional space with one-dimensional time, forming a continuum essential for understanding the universe's mechanics. It simplifies physical theories by treating time as a fourth dimension that cannot be separated from space, especially in relativistic contexts. The Earth exists within this spacetime framework, rather than above it, meaning everything in the universe is contained within spacetime. Visual representations may depict spacetime as a surface, but they cannot fully capture its complexity. Understanding spacetime is crucial for grasping the fundamental workings of the universe.