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Line 1: − + − + − General Relativity (GR) is a theory which explains the laws of motion as viewed from accelerating reference frames and includes a geometric explanation for gravity. This theory was developed by [[David Hilbert]] and [[Albert Einstein]] as an extension of the postulates of Special Relativity.<ref>"[T]he German mathematician David Hilbert submitted an article containing the correct field equations for general relativity five days before Einstein."[http://nobelprize.org/educational_games/physics/relativity/history-1.html Nobel Prize historical account]</ref> A dramatic but later discredited claim by Sir [[Arthur Eddington]] of experimental proof of General Relativity in 1919 made Einstein a household name.+ − − == Special Relativity == − Special Relativity is usually explained in terms of two assumptions (postulates): − − # ''The [[speed of light]] is constant for all (inertial) observers, regardless of their velocities relative to each other.'' − # ''The laws of physics are identical in all inertial reference frames.'' − − In layman's terms, these two assumptions can be restated as: − # It is impossible ever to transmit information faster than the speed of light.<ref>This assumption is commonly restated in this manner. For example, an discussion of hypothetical [[tachyons]] says, "about using tachyons to transmit information faster than the speed of light, '''in violation of Special Relativity'''?[http://www.math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html] However, some question whether the Theory of Special Relativity really restricts faster-than-light communication of information.</ref> − − # The laws of physics are identical, without any variation, no matter how fast something is traveling (in the absence of acceleration). − − Special Relativity (SR) was initially developed by [[Henri Poincaré]] and [[Hendrik Lorentz]], working on problems in electrodynamics and the [[Michelson-Morley experiment]], which had not found any sign of [[aether (science)|luminiferous aether]], which was believed to be the substance which carried electromagnetic waves. Special relativity alters [[Isaac Newton]]'s laws of motion by assuming that the speed of light will be the same for all observers, despite their relative velocities and the source of the light. (Therefore, if A sends a beam of light to B, and both measure the speed, it will be the same for both, no matter what the relative velocity of A and B. In Newtonian/Galilean mechanics, If A sends a physical object at a particular velocity towards B, and nothing slows it, the velocity of the object relative to B depends on the velocities of the object and of B relative to A.) − − At low speeds (relative to light-speed), the Einstein-Lorentz relativity equations are equivalent to Newton's equations. The famous equation attributed to Einstein, ''E=mc<sup>2</sup>'', describes the relationship between energy and the rest mass of a body. −
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'''Relativity''' refers to two closely-related theories in [[physics]], and to a principle which led to the first theory. Special relativity (SR) is a theory which describes the laws of motion for non-accelerating bodies traveling at a significant fraction of the speed of light. At speeds approaching zero, Special Relativity is identical to Newton's Laws of Motion. Special Relativity was developed by [[Hendrik Lorentz]], [[Henri Poincaré]], and [[Albert Einstein]].
'''Relativity''' refers to two closely-related theories in [[physics]], and to a principle which led to the first theory. Special relativity (SR) is a theory which describes the laws of motion for non-accelerating bodies traveling at a significant fraction of the speed of light. At speeds approaching zero, Special Relativity is identical to Newton's Laws of Motion. Special Relativity was developed by [[Hendrik Lorentz]], [[Henri .ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html] However, some question whether the Theory of Special Relativity really restricts faster-than-light communication of information.</ref>
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# The laws of physics are identical, without any variation, in every location throughout the universe.
Relativity is essential for massive or fast-moving bodies; for electromagnetism; for light and other radiation; for quantum field theory; for spin; and for nuclear energy. Particles at low mass and low speed 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).
Relativity is essential for massive or fast-moving bodies; for electromagnetism; for light and other radiation; for quantum field theory; for spin; and for nuclear energy. Particles at low mass and low speed 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).