In general relativity, geodesics are the straightest possible paths that objects follow through curved spacetime. While in flat, Euclidean space a geodesic is just a straight line, in the curved geometry of spacetime—shaped by mass and energy—geodesics appear curved to an outside observer.
Freely falling objects, like satellites orbiting Earth or planets around the Sun, follow geodesics. They move under gravity alone, without any force acting on them (in the relativistic sense), simply following the natural contours of spacetime curvature.
Einstein’s theory redefines gravity not as a force, but as the result of objects moving along these curved geodesics. The shape of spacetime itself determines how objects move, and those motions are geodesics dictated by the distribution of mass and energy.
Understanding geodesics is essential for describing everything from planetary orbits and light bending near stars to the motion of objects near black holes.