"General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics."
A theory that expands on the special theory of relativity, describing the relationship between gravity and space-time.
Special Theory of Relativity: The foundation on which General Theory of Relativity is built, it explains the relationship between space and time in the absence of gravity.
The Equivalence Principle: The fundamental principle behind General Theory of Relativity, it states that the effects of gravitation cannot be distinguished from the effects of acceleration.
The Spacetime Continuum: The idea that space and time are not independent of each other, but are interconnected in a four-dimensional continuum.
Curvature of Spacetime: The idea that matter and energy curve spacetime, leading to the effects of gravity.
Tensor Calculus: A mathematical framework used to describe the curvature of spacetime in General Theory of Relativity.
The Geodesic Equation: Describes the path a free particle takes in a curved spacetime, and is central to the understanding of gravity.
The Schwarzschild Metric: Describes the geometry of spacetime around a non-rotating, spherically symmetric mass, such as a black hole or a star.
The Cosmological Constant: Introduced by Einstein to counteract the effects of gravity on the universe, it is now seen as a possible explanation for the accelerating expansion of the universe.
The Einstein Field Equations: The central equation of General Theory of Relativity, it describes the curvature of spacetime in terms of the distribution of matter and energy.
Gravitational Waves: The ripples in spacetime that are produced by the acceleration of massive objects, they have been directly detected for the first time in 2015.
Black Holes: The gravitational collapse of a massive object to a point of infinite density, it is one of the most fascinating predictions of General Theory of Relativity.
Cosmology: The study of the large-scale structure and evolution of the universe, General Theory of Relativity provides the framework for understanding the evolution of the universe from its origins to the present day.
Classical General Theory of Relativity: This is the original, foundational theory developed by Albert Einstein that describes the behavior of gravity and its effects on the spacetime continuum.
Quantum General Theory of Relativity: This is a theoretical framework that combines the principles of general relativity with quantum mechanics in order to account for very small-scale phenomena.
String Theory: This is a theoretical framework that posits that the fundamental building blocks of the universe are not point-like particles, but rather one-dimensional objects called strings. String theory is often seen as a potential unification of general relativity and quantum theory.
Loop Quantum Gravity: This is a theoretical framework that posits that space and time are fundamentally discrete, rather than continuous. It seeks to reconcile general relativity with quantum mechanics by using a mathematical language based on loops and networks rather than the traditional spacetime geometry.
Modified Gravity Theories: These are theories that propose modifications to the equations of general relativity in order to explain certain phenomena such as dark matter and dark energy. These modifications often involve adding new fields or adjusting the fundamental constants of the theory.
Conformal Gravity: This is a theory that proposes a modification to the theory of general relativity that involves replacing the metric tensor (which describes the curvature of spacetime) with a new geometrical object called the (conformal) Weyl tensor. The theory aims to explain dark matter and dark energy without resorting to exotic new particles or fields.
Emergent Gravity: This is a theoretical framework that proposes that the effects of gravity emerge from the collective behavior of large numbers of microscopic entities, rather than being a fundamental force in its own right. The theory is still in its infancy and much research is needed in order to fully flesh out its predictions and implications.
"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 four-dimensional spacetime."
"In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present."
"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, and singularities/black holes."
"So far, all tests of general relativity 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 cosmology, thus leading to the discovery of the Big Bang and cosmic microwave background radiation."
"Reconciliation of general relativity with the laws of quantum physics remains a problem, however, as there is a lack of a self-consistent theory of quantum gravity."
"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."
"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 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 base of cosmological models of an expanding universe."
"Widely acknowledged as a theory of extraordinary beauty, general relativity has often been described as the most beautiful of all existing physical theories."
"General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915."
"General relativity provides a unified description of gravity as a geometric property of space and time or four-dimensional spacetime."
"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, and singularities/black holes."
"So far, all tests of general relativity 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 cosmology, thus leading to the discovery of the Big Bang and cosmic microwave background radiation."
"Reconciliation of general relativity with the laws of quantum physics remains a problem, however, as there is a lack of a self-consistent theory of quantum gravity."