Einstein explained · 1915
General Relativity
General relativity explains gravity as the curvature of spacetime rather than as a simple force acting across space.
matter + energy → curved spacetime
CURVED SPACETIME
What it means
Matter and energy change the geometry of spacetime. Objects in free fall then follow the natural paths through that curved spacetime.
Einstein's contribution
Einstein completed the core field equations in November 1915 after years of work on the equivalence principle and new mathematics. The theory successfully explained Mercury's unusual orbit and predicted the bending of light.
Why it matters
General relativity is used to understand black holes, gravitational lensing, gravitational time effects, gravitational waves and the large-scale universe.
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Einstein’s key theories and contributions
1905Special RelativityHow motion changes measurements of space and time while the speed of light stays constant.Read explainer →1905Mass–Energy EquivalenceWhy mass and energy are connected by Einstein's famous relation E = mc².Read explainer →1907Equivalence PrincipleWhy free fall and acceleration gave Einstein the starting point for a new theory of gravity.Read explainer →1907Gravitational RedshiftHow gravity changes the frequency of light and the rate at which clocks run.Read explainer →1916–1918Gravitational WavesHow changing masses can send ripples through spacetime at the speed of light.Read explainer →1916–1917Quantum Theory of RadiationHow atoms absorb and emit light, including Einstein's prediction of stimulated emission.Read explainer →1917Cosmological ConstantWhy Einstein added Λ to his gravity equations and how the term returned in modern cosmology.Read explainer →