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→Special Relativity: Again, even classically, light travels at finite speed. This has been known for quite a while.
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.
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.
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 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 ==
== General Relativity ==