Geodesic motion

In general relativity, geodesic motion is the path a freely falling object follows through curved spacetime. It is often described as the straightest possible path when gravity is treated as spacetime curvature rather than a Newtonian force.

In the relativistic view, Earth approximately follows a geodesic in the curved spacetime produced mainly by the Sun. Small corrections from other planets, tides, and non-gravitational effects mean the real Solar System is more complicated than a two-body example.

In flat space, a geodesic is just a straight line. On a curved surface or in curved spacetime, the geodesic can look curved from the outside, like a great-circle route on Earth.

Light follows null geodesics, which are paths through spacetime with zero spacetime interval. This is why massive objects such as the Sun can bend starlight, a prediction famously tested during the 1919 solar eclipse observations.