# General relativity

general theory of relativitygeneral relativity theoryrelativitytheory of general relativitygeneral relativisticrelativisticspacetime curvaturegeneralspace-time curvatureGeneral relativity resources
General relativity (GR), also known as the general theory of relativity (GTR), is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.wikipedia
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### Albert Einstein

EinsteinEinsteinianA. Einstein
General relativity (GR), also known as the general theory of relativity (GTR), is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.
He subsequently realized that the principle of relativity could be extended to gravitational fields, and published a paper on general relativity in 1916 introducing his theory of gravitation.

### Theory of relativity

relativityrelativisticrelativity theory
General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime.
The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity.

### Tests of general relativity

confirmedanomalous precessionclassical tests of general relativity
The predictions of general relativity in relation to classical physics have been confirmed in all observations and experiments to date.
Tests of general relativity serve to establish observational evidence for the theory of general relativity.

### Gravitational lens

gravitational lensinggravitationally lenseddeflection of light
Examples of such differences include gravitational time dilation, gravitational lensing, the gravitational redshift of light, and the gravitational time delay.
This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein's general theory of relativity.

### Special relativity

special theory of relativityrelativisticspecial
General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime.
Until Einstein developed general relativity, introducing a curved spacetime to incorporate gravity, the phrase "special relativity" was not used.

### Alternatives to general relativity

Classical theories of gravitationmodified gravityalternative theories of gravity
Although general relativity is not the only relativistic theory of gravity, it is the simplest theory that is consistent with experimental data.
Alternatives to general relativity are physical theories that attempt to describe the phenomenon of gravitation in competition to Einstein's theory of general relativity.

### Gravitational redshift

gravitational red shiftgravitationally redshiftedEinstein shift
Examples of such differences include gravitational time dilation, gravitational lensing, the gravitational redshift of light, and the gravitational time delay.
In Einstein's general theory of relativity, the gravitational redshift is the phenomenon that clocks in a gravitational field tick slower when observed by a distant observer.

### Quantum gravity

quantum theory of gravityquantum theories of gravityQuantization of gravity
However, unanswered questions remain, the most fundamental being how general relativity can be reconciled with the laws of quantum physics to produce a complete and self-consistent theory of quantum gravity.
The current understanding of gravity is based on Albert Einstein's general theory of relativity, which is formulated within the framework of classical physics.

### Gravitational wave

General relativity also predicts the existence of gravitational waves, which have since been observed directly by the physics collaboration LIGO.
They were proposed by Henri Poincaré in 1905 and subsequently predicted in 1916 by Albert Einstein on the basis of his general theory of relativity.

### Physical cosmology

cosmologycosmologicalcosmologist
In addition, general relativity is the basis of current cosmological models of a consistently expanding universe.
Physical cosmology, as it is now understood, began with the development in 1915 of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond the Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding.

### Scientific theory

theoryscientific theoriestheories
General relativity (GR), also known as the general theory of relativity (GTR), is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.
These qualities are certainly true of such established theories as special and general relativity, quantum mechanics, plate tectonics, the modern evolutionary synthesis, etc.

### Space

spatialphysical spacereal space
General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime.
According to Albert Einstein's theory of general relativity, space around gravitational fields deviates from Euclidean space.

### Gravity

gravitationgravitationalgravitational force
General relativity (GR), also known as the general theory of relativity (GTR), is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.
Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon.

### Differential geometry

differentialdifferential geometerdifferential geometry and topology
General relativity (GR), also known as the general theory of relativity (GTR), is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.
A special case of this is a Lorentzian manifold, which is the mathematical basis of Einstein's general relativity theory of gravity.

### History of general relativity

Golden age of general relativityessentialproblems in astronomy
Yet the theory entered the mainstream of theoretical physics and astrophysics only with the developments between approximately 1960 and 1975, now known as the golden age of general relativity.
General relativity (GR) is a theory of gravitation that was developed by Albert Einstein between 1907 and 1915, with contributions by many others after 1915.

### Arthur Eddington

Arthur Stanley EddingtonSir Arthur EddingtonEddington
Similarly, a 1919 expedition led by Eddington confirmed general relativity's prediction for the deflection of starlight by the Sun during the total solar eclipse of May 29, 1919, making Einstein instantly famous.
Eddington wrote a number of articles that announced and explained Einstein's theory of general relativity to the English-speaking world.

### Cosmological constant

cosmological constant problemcosmological termexpansion
In line with contemporary thinking, he assumed a static universe, adding a new parameter to his original field equations—the cosmological constant—to match that observational presumption.
In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) is the energy density of space, or vacuum energy, that arises in Albert Einstein's field equations of general relativity.

### Bernhard Riemann

RiemannGeorg Friedrich Bernhard RiemannRiemann, Bernhard
The 19th century mathematician Bernhard Riemann's non-Euclidean geometry, called Riemannian Geometry, provided the key mathematical framework which Einstein fit his physical ideas of gravity on, and enabled him to develop general relativity.
Through his pioneering contributions to differential geometry, Riemann laid the foundations of the mathematics of general relativity.

### Karl Schwarzschild

SchwarzschildKarlSchwarzschild, Karl
But as early as 1916, the astrophysicist Karl Schwarzschild found the first non-trivial exact solution to the Einstein field equations, the Schwarzschild metric.
Schwarzschild provided the first exact solution to the Einstein field equations of general relativity, for the limited case of a single spherical non-rotating mass, which he accomplished in 1915, the same year that Einstein first introduced general relativity.

### Gravitational time dilation

freezing both in timegoes more slowlygravity's effect on time
Examples of such differences include gravitational time dilation, gravitational lensing, the gravitational redshift of light, and the gravitational time delay.
In general relativity, it is considered to be a difference in the passage of proper time at different positions as described by a metric tensor of space-time.

### Stellar black hole

stellar-mass black holestellar mass black holeblack holes
For example, microquasars and active galactic nuclei result from the presence of stellar black holes and supermassive black holes, respectively.
In the theory of general relativity, a black hole could exist of any mass. The lower the mass, the higher the density of matter has to be in order to form a black hole.

### Expansion of the universe

expanding universeexpandingexpansion of space
In addition, general relativity is the basis of current cosmological models of a consistently expanding universe.
While special relativity prohibits objects from moving faster than light with respect to a local reference frame where spacetime can be treated as flat and unchanging, it does not apply to situations where spacetime curvature or evolution in time become important.

### Universe

physical worldThe Universeuniverses
In 1917, Einstein applied his theory to the universe as a whole, initiating the field of relativistic cosmology.
The model is based on general relativity and on simplifying assumptions such as homogeneity and isotropy of space.

### Astrophysics

astrophysicistastrophysicaltheoretical astrophysics
Einstein's theory has important astrophysical implications.
Topics also studied by theoretical astrophysicists include Solar System formation and evolution; stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity, special relativity, quantum and physical cosmology, including string cosmology and astroparticle physics.

### Classical mechanics

Newtonian mechanicsNewtonian physicsclassical
At the base of classical mechanics is the notion that a body's motion can be described as a combination of free (or inertial) motion, and deviations from this free motion.
In case that objects become extremely massive, general relativity becomes applicable.