Spacetime

Spacetime is the four-dimensional framework of three spatial dimensions and one time dimension in which physical events are located. In general relativity, its geometry encodes gravity.

Event (relativity): An occurrence specified by a particular position in space and time. Spacetime assigns each physical occurrence a location across all four dimensions.
Einstein field equations: Equations relating spacetime curvature to the distribution of matter and energy. They express how matter and energy shape the geometry of spacetime.
Special relativity: A theory of space, time, and motion for observers in inertial frames, excluding gravity. It established the four-dimensional spacetime framework for observers in uniform motion.
Global Positioning System: A satellite navigation system that determines positions using timed radio signals. Its clock corrections account for both special-relativistic motion and gravitational time dilation.
Newtonian mechanics: A classical theory describing motion through absolute space and time under forces. It treats gravity as a force in fixed space and time rather than spacetime curvature.
Minkowski spacetime: Flat four-dimensional spacetime used to describe special relativity. It provides the simplest spacetime geometry, without gravity or curvature.
Geodesic: A locally straight path defined by the geometry of a space or spacetime. Freely falling bodies follow geodesics in curved spacetime.
Hermann Minkowski: A mathematician who formulated the geometric interpretation of special relativity. His 1908 formulation made space and time parts of a single geometric structure.
Black hole: A region of spacetime whose gravity prevents anything inside its event horizon from escaping. Its defining boundary is a causal feature of spacetime geometry.
Euclidean space: A flat geometric space governed by Euclid's axioms and distance rules. Its purely spatial geometry lacks spacetime's time dimension and causal structure.

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