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Line 6: − − The general theory of relativity is a ''metric theory,'' sometimes also called a ''geometric theory.'' Metric theories describe physical phenomena in terms of [[differential geometry]]. This stands in contrast to Isaac Newton's [[Law of Universal Gravitation]], which described gravity in terms of a [[vector field]]. In the case of general relativity, the theory relates ''stress-energy'' — an extension of the concept of [[mass]] — and the [[curvature]] of [[spacetime]]. In the words of physicist John Wheeler, "Space tells matter how to move, matter tells space how to curve."<ref>Misner, Thorne & Wheeler. ''Gravitation.'' (1973)</ref> Line 18:
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General theory of relativity (view source)
Revision as of 16:14, November 15, 2009
, 16:14, November 15, 2009I messed up Kate's paragraph order (again!) Sorry.
General relativity, like [[quantum mechanics]] (the other of the two theories comprising "modern physics") both have reputations for being notoriously complicated and difficult to understand. In fact, in the early decades of the 20<sup>th</sup> century, general relativity had a sort of cult status in this regard. General relativity and quantum mechanics are both advanced college-level and postgraduate level topics. Hence this article can't possibly give a comprehensive explation of general relativity at the expert level. But we will attempt to give a rough outline, for lay people, of the general relativistic formulation of gravity.
General relativity, like [[quantum mechanics]] (the other of the two theories comprising "modern physics") both have reputations for being notoriously complicated and difficult to understand. In fact, in the early decades of the 20<sup>th</sup> century, general relativity had a sort of cult status in this regard. General relativity and quantum mechanics are both advanced college-level and postgraduate level topics. Hence this article can't possibly give a comprehensive explation of general relativity at the expert level. But we will attempt to give a rough outline, for lay people, of the general relativistic formulation of gravity.
In the [[weak field approximation]], where velocities of moving objects are low and gravitational fields are not very severe, the theory of general relativity is said to ''reduce to'' the law of universal gravitation. That is to say, under those circumstances the equations of general relativity are mathematically equivalent to the equations of Newtonian gravitation.
In the [[weak field approximation]], where velocities of moving objects are low and gravitational fields are not very severe, the theory of general relativity is said to ''reduce to'' the law of universal gravitation. That is to say, under those circumstances the equations of general relativity are mathematically equivalent to the equations of Newtonian gravitation.
The theory was inspired by a thought experiment developed by Einstein involving two elevators. The first elevator is stationary on the Earth, while the other is being pulled through space at a constant acceleration of g. Einstein realized that any physical experiment carried out in the elevators would give the same result. This realization is known as the [[equivalence principle]] and it states that accelerating frames of reference and gravitational fields are indistinguishable. General relativity is the theory of gravity that incorporates special relativity and the equivalence principle.
The theory was inspired by a thought experiment developed by Einstein involving two elevators. The first elevator is stationary on the Earth, while the other is being pulled through space at a constant acceleration of g. Einstein realized that any physical experiment carried out in the elevators would give the same result. This realization is known as the [[equivalence principle]] and it states that accelerating frames of reference and gravitational fields are indistinguishable. General relativity is the theory of gravity that incorporates special relativity and the equivalence principle.
The general theory of relativity is a ''metric theory,'' sometimes also called a ''geometric theory.'' Metric theories describe physical phenomena in terms of [[differential geometry]]. This stands in contrast to Isaac Newton's [[Law of Universal Gravitation]], which described gravity in terms of a [[vector field]]. In the case of general relativity, the theory relates ''stress-energy'' — an extension of the concept of [[mass]] — and the [[curvature]] of [[spacetime]]. In the words of physicist John Wheeler, "Space tells matter how to move, matter tells space how to curve."<ref>Misner, Thorne & Wheeler. ''Gravitation.'' (1973)</ref>
==Coordinate Systems and Spacetime Diagrams==
==Coordinate Systems and Spacetime Diagrams==