Theory of relativity

The framework developed by Albert Einstein in which space and time are interrelated, encompassing special relativity and general relativity.

Spacetime: The four-dimensional continuum combining three dimensions of space with one dimension of time. Relativity describes events and motion within a unified four-dimensional structure.
Special relativity: Einstein's theory of space and time for observers in inertial frames, with the speed of light invariant. It supplies the framework's account of motion without gravity.
Albert Einstein: A German-born theoretical physicist who developed special and general relativity. He formulated both theories that make up the framework.
Gravitational lens: A massive object that bends light from a more distant source through its gravitational field. The bending of light tests general relativity and reveals otherwise hidden matter.
Galilean relativity: The classical principle that mechanical laws are the same in all inertial frames related by Galilean transformations. It assumes absolute time and does not preserve the speed of light across frames.
Frame of reference: A coordinate system and clock convention used to assign positions and times to events. Relativistic measurements depend on the frame used to describe events.
General relativity: Einstein's theory of gravity in which matter and energy curve spacetime. It extends relativistic reasoning to gravity and accelerated frames.
Michelson–Morley experiment: An 1887 experiment that found no detectable difference in light's speed due to Earth's motion through the hypothesized ether. Its null result sharpened the problem of reconciling light with motion.
Gravitational wave: A propagating disturbance in spacetime curvature generated by accelerating masses. Their detection confirmed a dynamic prediction of general relativity.
Newtonian mechanics: The classical framework describing motion through Newton's laws of motion and universal gravitation. It approximates relativity at low speeds and weak gravitational fields.

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