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Special relativity (1905) governs physics without gravity; general relativity (1915) explains gravity as spacetime curvature.
Albert Einstein’s theory of relativity consists of two related theories: special relativity (published in 1905) and general relativity (published in 1915). Special relativity applies to all physical phenomena in the absence of gravity, while general relativity explains gravity and its relationship to the forces of nature, extending the ideas to cosmology and astrophysics. Special relativity is built on two postulates: (1) the laws of physics are the same for all observers in inertial frames, and (2) the speed of light in vacuum is constant for all observers, regardless of their relative motion. These lead to major consequences such as relativity of simultaneity, time dilation, length contraction, a finite maximum speed (the speed of light), and mass–energy equivalence (E = mc²). A key mathematical feature is the replacement of Galilean transformations with Lorentz transformations. General relativity develops from the equivalence principle, which links accelerated motion to being in a gravitational field, implying that free fall is inertial motion. Einstein then reformulated gravity as the curvature of spacetime, expressed through the Einstein field equations that relate spacetime curvature to mass, energy, and momentum. The theory predicts effects such as gravitational time dilation, light deflection, frame-dragging, orbital precession, and the expansion of the universe, and it has been repeatedly confirmed by experiments and observations. Practical technologies (notably satellite navigation systems like GPS) also require relativistic corrections for precision.
Special relativity (1905) governs physics without gravity; general relativity (1915) explains gravity as spacetime curvature.
Special relativity is based on the relativity principle and the constancy of the speed of light, yielding time dilation, length contraction, and E = mc².
General relativity is based on the equivalence principle and the Einstein field equations, predicting gravitational time dilation, light bending, frame-dragging, and cosmic expansion.
Both theories are experimentally testable and have been validated by classic and modern tests; relativistic effects are also essential for real-world engineering like GPS.
A theory describing the structure of spacetime for phenomena in the absence of gravity, based on the relativity principle and the constant speed of light.
A theory of gravitation in which gravity is explained by the curvature of spacetime, governed by the Einstein field equations.
The principle stating that accelerated motion and being at rest in a gravitational field are physically indistinguishable, implying free fall is inertial motion.
The mathematical transformations that replace Galilean transformations in special relativity and preserve the speed of light between inertial frames.
Equations that relate the curvature of spacetime (through a metric tensor) to the distribution of mass, energy, and momentum.
The idea that two events that are simultaneous for one observer may not be simultaneous for another observer in relative motion.
The prediction that clocks run more slowly in stronger gravitational fields (deeper gravitational wells).
A general-relativistic effect where rotating masses influence the motion of spacetime itself, affecting nearby objects and light.
The special-relativistic relation stating that mass and energy are interchangeable forms of the same physical quantity.
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