General relativity

General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the <a href="/facts/Differential_geometry/c04XmyLu">geometric</a> <a href="/facts/Scientific_theory/moMsLrUn">theory</a> of <a href="/facts/Gravitation/bqAN7DdQ">gravitation</a> published by <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a> in 1915 and is the current description of gravitation in <a href="/facts/Modern_physics/J9Kko1qU">modern physics</a>. General <a href="/facts/Theory_of_relativity/qGHj3eTC">relativity</a> generalizes <a href="/facts/Special_relativity/vsFFc63E">special relativity</a> and refines <a href="/facts/Newton%27s_law_of_universal_gravitation/F6qH2XC3">Newton's law of universal gravitation</a>, providing a unified description of gravity as a geometric property of <a href="/facts/Space/tq6LUM3C">space</a> and <a href="/facts/Time_in_physics/5s0grGmk">time</a>, or <a href="/facts/Four-dimensional_space/vFQd0M7T">four-dimensional</a> <a href="/facts/Spacetime/uRIN1x4b">spacetime</a>. In particular, the <a href="/facts/Curvature/RFCAEsj8">curvature</a> of spacetime is directly related to the <a href="/facts/Energy/wd8PrQM7">energy</a> and <a href="/facts/Momentum/TTkGv5eY">momentum</a> of whatever is 
present, including <a href="/facts/Matter/osyc04UN">matter</a> and <a href="/facts/Radiation/RwMocyeq">radiation</a>. The relation is specified by the <a href="/facts/Einstein_field_equations/j2rJTzW9">Einstein field equations</a>, a system of second-order <a href="/facts/Partial_differential_equation/DyPsBlv7">partial differential equations</a>.
<a href="/facts/Newton%27s_law_of_universal_gravitation/F6qH2XC3">Newton's law of universal gravitation</a>, which describes classical gravity, can be seen as a prediction of general relativity for the almost flat spacetime geometry around stationary mass distributions. Some predictions of general relativity, however, are beyond <a href="/facts/Newton%27s_law_of_universal_gravitation/F6qH2XC3">Newton's law of universal gravitation</a> in <a href="/facts/Classical_physics/gGnINVPE">classical physics</a>. These predictions concern the passage of time, the <a href="/facts/Geometry/wTQf5ffQ">geometry</a> of space, the motion of bodies in <a href="/facts/Free_fall/os0d9qkt">free fall</a>, and the propagation of light, and include <a href="/facts/Gravitational_time_dilation/z4XG7SYA">gravitational time dilation</a>, <a href="/facts/Gravitational_lens/LmxzvLs8">gravitational lensing</a>, the <a href="/facts/Gravitational_redshift/cEFgB3Ns">gravitational redshift</a> of light, the <a href="/facts/Shapiro_time_delay/waUI1dg3">Shapiro time delay</a> and <a href="/facts/Gravitational_singularity/BptlItux">singularities</a>/<a href="/facts/Black_holes/1r2lmkcF">black holes</a>. So far, all <a href="/facts/Tests_of_general_relativity/yDgwtNrw">tests of general relativity</a> have been shown to be in agreement with the theory. The time-dependent solutions of general relativity enable us to talk about the history of the universe and have provided the modern framework for <a href="/facts/Cosmology/yM19zM7Y">cosmology</a>, thus leading to the discovery of the <a href="/facts/Big_Bang/I5T1vTnv">Big Bang</a> and <a href="/facts/Cosmic_microwave_background/ThB2HkLS">cosmic microwave background</a> radiation. Despite the introduction of a number of <a href="/facts/Alternatives_to_general_relativity/E51N6lSg">alternative theories</a>, general relativity continues to be the simplest theory consistent with <a href="/facts/Experimental_data/PKMa2Fvw">experimental data</a>.
Reconciliation of general relativity with the laws of <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum physics</a> remains a problem, however, as there is a lack of a self-consistent theory of <a href="/facts/Quantum_gravity/t7whBMNE">quantum gravity</a>. It is not yet known how gravity can be <a href="/facts/Theory_of_everything/rpossh4t">unified</a> with the three non-gravitational forces: <a href="/facts/Strong_interaction/JjRsKcLg">strong</a>, <a href="/facts/Weak_interaction/f6upmKMs">weak</a> and <a href="/facts/Electromagnetism/oAkmALHT">electromagnetic</a>.
Einstein's theory has <a href="/facts/Astrophysical/krFPRWLA">astrophysical</a> implications, including the prediction of <a href="/facts/Black_holes/1r2lmkcF">black holes</a>—regions of space in which space and time are distorted in such a way that nothing, not even <a href="/facts/Photon/mFNhAEzA">light</a>, can escape from them. Black holes are the end-state for <a href="/facts/Massive_star/PFbd6ICx">massive stars</a>. <a href="/facts/Microquasar/qINUAeEy">Microquasars</a> and <a href="/facts/Active_galactic_nucleus/qT1owvXz">active galactic nuclei</a> are believed to be <a href="/facts/Stellar_black_hole/8cz1uzAe">stellar black holes</a> and <a href="/facts/Supermassive_black_hole/BcuTx8Q5">supermassive black holes</a>. It also predicts <a href="/facts/Gravitational_lensing/LmxzvLs8">gravitational lensing</a>, where the bending of light results in multiple images of the same distant astronomical phenomenon. Other predictions include the existence of <a href="/facts/Gravitational_wave/4XWN3NtG">gravitational waves</a>, which have been <a href="/facts/List_of_gravitational_wave_observations/PlWE2j7x">observed directly</a> by the physics collaboration <a href="/facts/LIGO/jX6jyJzM">LIGO</a> and other observatories. In addition, general relativity has provided the base of <a href="/facts/Physical_cosmology/ww4ChbEq">cosmological</a> models of an <a href="/facts/Metric_expansion_of_space/f6Uvt79B">expanding universe</a>.
Widely acknowledged as a theory of extraordinary <a href="/facts/Mathematical_beauty/HYwRap01">beauty</a>, general relativity has often been described as the most beautiful of all existing physical theories.

General relativity open-in-new

General relativity