The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity.[1] Special relativity applies to elementary particles and their interactions, describing all their physical phenomena except gravity. General relativity explains the law of gravitation and its relation to other forces of nature.
Development and Acceptance
Albert Einstein published the theory of special relativity in 1905, building on many theoretical results and empirical findings obtained by Albert A. Michelson, Hendrik Lorentz, Henri Poincaré and others
- Einstein developed general relativity between 1907 and 1915, with contributions by many others after 1915
- The final form of general relativity was published in 1916
- By the 1920s, the physics community understood and accepted special relativity
- Around 1960, general relativity became central to physics and astronomy
Further reading
Einstein, Albert (2005). Relativity: The Special and General Theory. New York, NY: Henry Holt and Company. ISBN 978-0-9780486470115-1.
- The Meaning of Relativity (5 Ed.). Princeton University Press. Einstein’s Essays in Science, Translated by Alan Harris (Dover ed.). Mineola, N.Y.: Dover Publications. ISBN 0875483526.
Special Relativity
A theory of the structure of spacetime based on two postulates that are contradictory in classical mechanics
- Relativity of simultaneity
- Time dilation
- Length contraction
- Maximum speed is finite
- Mass-energy equivalence
- The defining feature of special relativity is the replacement of the Galilean transformations of classical mechanics by the Lorentz transformations, known as relativistic mass
Tests of General Relativity
General relativity has also been confirmed many times, the classic experiments being the perihelion precession of Mercury’s orbit, the deflection of light by the Sun, and the gravitational redshift of light.
General Relativity
General relativity is a theory of gravitation developed by Einstein in the years 1907-1915
- The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field are physically identical
- Free fall is inertial motion: an object in free fall is falling because that is how objects move when there is no force being exerted on them, instead of this being due to the force of gravity as is the case in classical mechanics
- Einstein first proposed that spacetime is curved, and then devised the Einstein field equations which relate the curvature of spacetime with the mass, energy, and any momentum within it
- Some of the consequences of gravity include: Clocks run slower in deeper gravitational wells, orbits precess in a way unexpected in Newton’s theory of gravity, and rays of light bend in the presence of a strong gravitational field
Modern applications
Relativitistic effects are important practical engineering concerns. Satellite-based measurement needs to take into account relativistic effects, as each satellite is in motion relative to an Earth-bound user and is thus in a different frame of reference under the theory of relativity.
- Global positioning systems such as GPS, GLONASS, and the forthcoming Galileo, must account for all of the relatievistic effects.
Experimental evidence
Einstein stated that the theory of relativity belongs to a class of “principle-theories”.
Tests of special relativity
Relativity is a falsifiable theory: It makes predictions that can be tested by experiment.
- Einstein derived the Lorentz transformations from first principles in 1905, but three experiments allow the transformations to be induced from experimental evidence
- The Michelson-Morley experiment, the Kennedy-Thorndike experiment, and the Ives-Stilwell experiment
- All three were designed to detect second-order effects of the “aether wind,” the motion of the aether relative to the earth. The results were accepted by the scientific community.
