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The Theory of Relativity is a geometrical theory of gravitation, stating that the [[speed of light]] and laws of physics are constant for all observers, regardless of their velocities relative to each other.

The Theory of Relativity is a geometrical theory of gravitation, stating that the [[speed of light]] and laws of physics are constant for all (inertial) observers, regardless of their velocities relative to each other.

The theory of relativity was first proposed based on mathematical theory developed by [[Henri Poincaré]] and [[Hendrik Lorentz]]. This theory was not developed based on observation or experiments.  Poincaré and Lorentz pondered what would happen if the speed of light was constant in all frames of reference, and all laws of physics were the same in every (inertial) frame of reference no matter where it is or how fast it is traveling. This theory differs from [[Isaac Newton]]'s theory of gravitation by disposing with the idea of a universal, mutually agreeable scale of time (i.e. a universal clock that all times can refer to) and space (i.e. a universal sheet of "graph paper", which location refers to).  

The theory of relativity was first proposed based on mathematical theory developed by [[Henri Poincaré]] and [[Hendrik Lorentz]]. This theory differs from [[Isaac Newton]]'s theory of gravitation by disposing with the idea of a universal, mutually agreeable scale of time (i.e. a universal clock that all times can refer to) and space (i.e. a universal sheet of "graph paper", which location refers to).  

The famous equation attributed to Einstein, ''E=mc²'', describes the relationship between energy and the rest mass of a body.

The famous equation attributed to Einstein, ''E=mc²'', describes the relationship between energy and the rest mass of a body.

In general terms, relativity predicts that space-time can be curved by massive bodies, so that (for example) near a [[black hole]] the sum of the angles in a triangle is not exactly 180 degrees, time passes more rapidly away from a black hole than near it (for a distant observer) and other apparent violations of [[geometry]] and common sense.

In general terms, relativity predicts that space-time can be curved by massive bodies, so that (for example) near a [[black hole]] the sum of the angles in a triangle is not exactly 180 degrees, time passes more rapidly away from a black hole than near it (for a distant observer) and other apparent violations of [[geometry]] and common sense.

Relativity is important for massive or fast-moving bodies: at low mass and low speed, it can be accurately approximated by [[classical mechanics]] (such as [[Isaac Newton]]'s laws of motion). At the two extremes, modelling the behaviour of electrons requires that relativistic effects be taken into account (the chemically significant phenomenon of [[electron spin]] arises from relativity), and the course light passing through a region containing many massive bodies such as galaxies will be distorted ([[classical mechanics]], in which light travels with infinite speed in straight lines, does not predict this). These are both experimentally confirmed ([[electron spin]] was known before relativity arose, and telescopic observations confirm that galactic clusters distort the paths of the light passing through them).  

Relativity is important for massive or fast-moving bodies: at low mass and low speed, it can be accurately approximated by [[classical mechanics]] (such as [[Isaac Newton]]'s laws of motion). At the two extremes, modeling the behavior of electrons requires that relativistic effects be taken into account (the chemically significant phenomenon of [[electron spin]] arises from relativity), and the course light passing through a region containing many massive bodies such as galaxies will be distorted ([[classical mechanics]], in which light travels with infinite speed in straight lines, does not predict this). These are both experimentally confirmed ([[electron spin]] was known before relativity arose, and telescopic observations confirm that galactic clusters distort the paths of the light passing through them).  

General relativity successfully explains the seemingly anomalous precession of Mercury's perihelion.  While other explanations based in Newtonian gravity had been proposed, none were consistent with observation.

General relativity successfully explains the seemingly anomalous precession of Mercury's perihelion.  While other explanations based in Newtonian gravity had been proposed, none were consistent with observation.