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How does curved space-time affect the paths of planets and light?

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gravitational lens — gravity A galactic cluster, about five billion light-years away, produces a tremendous gravitational field that “bends” light around it. This lens produces multiple copies of a blue galaxy about twice as distant. Four images are visible in a circle surrounding the lens; a fifth is visible near the center of the picture, which was taken by the Hubble Space Telescope.

In general relativity, gravity is not a force but a consequence of the geometry of space-time. Massive objects, such as stars or galaxies, curve the space-time around them, and this curvature dictates how matter and light move.12

Geodesics and Motion

Objects in motion, including planets, follow the shortest natural paths through this curved geometry, known as geodesics. Rather than being pulled by a force, a planet orbits a star because it is following a geodesic path defined by the curvature of space-time. This geometric framework explains phenomena such as the anomalous advance of the perihelion of Mercury, which Newtonian physics could not fully account for.124

The Bending of Light

Light also follows these geodesics. When light passes near a massive body, its path is deflected by the curvature of space-time. This effect allows massive objects to act as a gravitational lens, bending and focusing light from distant sources, which can distort images or create multiple images of the same object.13