General Relativity

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General relativity

General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in May 1916 and is the accepted description of the gravitation of macroscopic objects in modern physics. General relativity generalizes special relativity and refines Isaac Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy, momentum, and stress of whatever is present, including matter and radiation. The relation is specified by the Einstein field equations, a system of second-order partial differential equations. John Archibald Wheeler summarized it: "Space-time tells matter how to move; matter tells space-time how to curve." Newton's law of universal gravitation, which describes gravity in classical mechanics, 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 Newton's law of universal gravitation in classical physics. These predictions concern the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light, and include gravitational time dilation, gravitational lensing, the gravitational redshift of light, the Shapiro time delay, singularities and black holes. So far, all tests of general relativity have been in agreement with the theory. The time-dependent solutions of general relativity enable us to extrapolate the history of the universe into the past and future, and have provided the modern framework for cosmology, thus leading to the discovery of the Big Bang and cosmic microwave background radiation. Despite the introduction of a number of alternative theories, general relativity continues to be the simplest theory consistent with experimental data. Reconciliation of general relativity with the laws of quantum physics remains a problem, however, as no self-consistent theory of quantum gravity has been found. It is not yet known how gravity can be unified with the three non-gravitational interactions: strong, weak and electromagnetic. Einstein's theory has astrophysical implications, including the prediction of black holes—regions of space in which space and time are distorted in such a way that nothing, not even light, can escape from them. Black holes are the end-state for massive stars. Microquasars and active galactic nuclei are believed to be stellar black holes and supermassive black holes. It also predicts gravitational lensing, where the bending of light results in distorted and multiple images of the same distant astronomical phenomenon. Other predictions include the existence of gravitational waves, which have been observed directly by the physics collaboration LIGO and other observatories. In addition, general relativity has provided the basis for cosmological models of an expanding universe. Widely acknowledged as a theory of extraordinary mathematical beauty, general relativity has often been described as the "most beautiful of all existing physical theories."

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• General relativity - Wikipedia

  General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in May 1916 and is the accepted description of the gravitation of macroscopic objects in modern physics. General relativity generalizes special relativity and refines Isaac Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy, momentum, and stress "Stress (mechanics)") of whatever is present, including matter and radiation. The relation is specified by the Einstein field equations, a system of second-order partial differential equations. John [...] General relativity is a metric "Metric (general relativity)") theory of gravitation. At its core are Einstein's equations, which describe the relation between the geometry of a four-dimensional pseudo-Riemannian manifold representing spacetime, and the distribution of energy, momentum and stress contained in that spacetime. Phenomena that in classical mechanics are ascribed to the action of the force of gravity (such as free-fall, orbital motion, and spacecraft trajectories), correspond to inertial motion within a curved geometry of spacetime in general relativity; there is no gravitational force deflecting objects from their natural, straight paths. Instead, gravity corresponds to changes in the properties of space and time, which in turn changes the straightest-possible paths that [...] Newton's law of universal gravitation, which describes gravity in classical mechanics, 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 Newton's law of universal gravitation in classical physics. These predictions concern the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light, and include gravitational time dilation, gravitational lensing, the gravitational redshift of light, the Shapiro time delay, singularities and black holes. So far, all tests of general relativity have been in agreement with the theory. The time-dependent solutions of general relativity enable us to extrapolate the history of the

• General Relativity | Physics | Research Starters | EBSCO Research

  RESEARCH STARTER # General Relativity General relativity is a fundamental theory in physics, formulated by Albert Einstein in 1915, that describes the effect of gravity as a curvature of space-time caused by mass. It represents a significant advancement over Newtonian gravity, emphasizing that gravity is not merely a force but a geometric property of space-time itself. In this framework, massive objects like stars and planets warp the fabric of space-time around them, influencing the motion of other objects and the path of light. This theory has profound implications for our understanding of the universe, including the dynamics of galaxies, the behavior of light, and the existence of phenomena such as black holes. [...] General relativity describes the universe in the terms of four dimensions: three dimensions in space and the fourth in time. This concept becomes clear when one thinks about the relationship between time and space. Since light travels at a finite pace, the objects that humans can see in the night sky are not seen as they are now, but as they were when their light originally left them. Light from the closest star to Earth has taken about four years to reach this planet, while the light from the nearest galaxy has taken more than 2 million years. From frames of reference located elsewhere in the universe, the relative positions of the stars and galaxies change, as does their relative distance in time. Therefore, space cannot be referred to without reference to time. In general relativity, [...] General relativity describes the universe in the terms of four dimensions: three dimensions in space and the fourth in time. This concept becomes clear when one thinks about the relationship between time and space. Since light travels at a finite pace, the objects that humans can see in the night sky are not seen as they are now, but as they were when their light originally left them. Light from the closest star to Earth has taken about four years to reach this planet, while the light from the nearest galaxy has taken more than 2 million years. From frames of reference located elsewhere in the universe, the relative positions of the stars and galaxies change, as does their relative distance in time. Therefore, space cannot be referred to without reference to time. In general relativity,

• Theory of relativity - Wikipedia

  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 (for example, when standing on the surface of the Earth) are physically identical. The upshot of this is that 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. This is incompatible with classical mechanics and special relativity because in those theories inertially moving objects cannot accelerate with respect to each other, but objects in free fall do so. To [...] Technically, general relativity is a theory of gravitation whose defining feature is its use of the Einstein field equations. The solutions of the field equations are metric tensors "Metric tensor (general relativity)") which define the topology of the spacetime and how objects move inertially. ## Experimental evidence [...] Simulation of the merger GW150914, showing spacetime distortion from gravity as the black holes orbit and merge The theory of relativity comprises two physics theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical phenomena in the absence of gravity. General relativity explains the law of gravitation and its relation to the forces of nature. It applies to the cosmological and astrophysical realm, including astronomy.

• General relativity | Gravitational Waves, Spacetime & Cosmology | Britannica

  general relativity, part of the wide-ranging physical theory of relativity formed by the German-born physicist Albert Einstein. It was conceived by Einstein in 1916. General relativity is concerned with gravity, one of the fundamental forces in the universe. Gravity defines macroscopic behaviour, and so general relativity describes large-scale physical phenomena. [...] General relativity follows from Einstein’s principle of equivalence: on a local scale it is impossible to distinguish between physical effects due to gravity and those due to acceleration. Gravity is treated as a geometric phenomenon that arises from the curvature of space-time. The solution of the field equations that describe general relativity can yield answers to different physical situations, such as planetary dynamics, the birth and death of stars, black holes, and the evolution of the universe. General relativity has been experimentally verified by observations of gravitational lenses, the orbit of the planet Mercury, the dilation of time in Earth’s gravitational field, and gravitational waves from merging black holes. (For a more detailed treatment of general relativity, see

• What Is Einstein's General Relativity Theory? | dummies

  Buy NowSubscribe on Perlego General relativity was Einstein’s theory of gravity, published in 1915, which extended special relativity to take into account non-inertial frames of reference — areas that are accelerating with respect to each other. General relativity takes the form of field equations, describing the curvature of space-time and the distribution of matter throughout space-time. The effects of matter and space-time on each other are what we perceive as gravity.

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