Einstein Relativity Learning Path

Two theories: special and general relativity

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.

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Development and acceptance timeline

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