General relativity

Einstein’s theory of gravitation describes gravity as the curvature of spacetime caused by matter and energy. It replaces Newtonian gravity with geometric laws that also predict phenomena such as black holes and gravitational waves.

Einstein field equations: Nonlinear equations relating spacetime curvature to the distribution of matter and energy. They state the central relation between geometry and physical sources in general relativity.
Schwarzschild metric: An exact solution of Einstein’s equations for the vacuum outside a spherical, nonrotating mass. It models the exterior gravitational field of idealized stars and black holes.
Albert Einstein: A theoretical physicist who developed special and general relativity and made major contributions to quantum theory. He formulated general relativity and presented its final field equations in 1915.
Newtonian gravity: A theory treating gravity as an attractive force between masses acting within absolute space and time. It approximates general relativity in weak gravitational fields and at low speeds.
Black hole information paradox: The apparent conflict between black hole evaporation and quantum-mechanical conservation of information. It exposes tension between semiclassical gravity, black hole thermodynamics, and quantum theory.
Geodesic: A locally straightest path through curved space or spacetime. Freely falling bodies follow spacetime geodesics when nongravitational forces are absent.
Kerr metric: An exact solution describing the spacetime around a rotating, uncharged mass. It captures frame dragging and is used to model rotating black holes.
Special relativity: A theory of space and time in inertial frames, built around the constancy of light speed. General relativity extends its spacetime framework to include gravity and accelerated frames.
Quantum gravity: A proposed framework for describing gravity according to quantum principles. General relativity is classical and does not provide a complete description of quantum spacetime.
Dark matter: A form of matter inferred from gravitational effects but not observed through emitted or absorbed light. Its gravitational influence is commonly modeled using general relativity, while its nature remains unknown.

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