General Relativity and Curved Spacetime

General Relativity as Geometric Gravity

General relativity is Einstein's geometric theory of gravity, published in 1916. It describes gravity not as a conventional force but as the curvature of four-dimensional spacetime caused by matter, energy, momentum, and stress. Freely falling objects follow geodesics, or the natural paths determined by spacetime geometry, while the Einstein field equations specify how stress-energy produces curvature. This framework generalizes special relativity and reduces to Newtonian gravity in weak gravitational fields and for slow-moving objects. The theory predicts effects beyond Newton's law, including gravitational time dilation, gravitational redshift, light deflection, gravitational lensing, the Shapiro time delay, black holes, singularities, and gravitational waves. Its predictions have been repeatedly confirmed, including the anomalous orbit of Mercury, the bending of starlight, observations of black holes, and direct detections of gravitational waves. General relativity also forms the foundation of modern cosmology and expanding-universe models, although reconciling it with quantum physics remains an unresolved challenge.

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Spacetime Curvature and Matter

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