Principle of relativity
From Wikipedia, the free encyclopedia
The principle of relativity, refers to relativity of uniform motion and its subsequent application to Albert Einstein's special relativity and general relativity.
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[edit] Galilean relativity
The principle of relativity was first explicitly enunciated by Galileo in 1632 in his Dialogue Concerning the Two Chief World Systems in terms of Galileo's ship. It essentially states that to all observers in constant motion, regardless of their position or velocity in the universe, all physical laws will appear the same. From this principle, it follows that an observer cannot determine either his absolute speed or direction of travel in space. It was later formulated by saying that absolute time and the laws of Newtonian mechanics and gravitation were invariant under Galilean Transformations.
[edit] Special relativity
Albert Einstein's 1905 paper "On the Electrodynamics of Moving Bodies" introduced the special theory of relativity. Special relativity considers that observers in inertial reference frames, which are in uniform motion relative to one another, cannot perform any experiment to determine which one of them is "stationary". This is actually Galileo's principle of relativity; Einstein's contribution was to explicitly include electromagnetism within this principle by replacing, in the formalism, the Galilean transformations with Lorentz transformations and to see that this led to many surprising consequences. In particular it overthrew the Newtonian concept of absolute time and required the speed of light in a vacuum to be the same for all these observers, regardless of their motion, or the motion of the source of the light, since the invariance of the speed of light is a consequence of the principle of relativity applied to Maxwell's equations of electromagnetism.
This is the strength of special relativity, that it can be derived from such a single, basic principle: the invariance of the laws of physics under a shift of inertial reference frames, known as Lorentz covariance.
[edit] General relativity
General relativity was developed by Einstein in the years 1907 - 1915. General relativity postulates that the global Lorentz covariance of special relativity becomes a local Lorentz covariance in the presence of matter. The presence of matter "curves" spacetime, and this curvature affects the path of free particles (and even the path of light). General relativity uses the mathematics of differential geometry and tensors in order to describe gravitation as an effect of the geometry of spacetime. This theory is based on the general principle of relativity, which requires all observers to experience the same laws of physics, not just those moving with uniform speed, hence its name.
[edit] See also
- Special relativity including Introduction to special relativity
- General relativity including Introduction to general relativity
- Galilean relativity
- List of publications in physics: Theory of relativity
[edit] References and links
See the special relativity references and the general relativity references.
[edit] External links
- Living Reviews in Relativity — An open access, peer-referred, solely online physics journal publishing invited reviews covering all areas of relativity research.
- Reflections on Relativity — A complete online course on Relativity.
- Relativity explained in words of four letters or less
- Briefing on Einstein's Theory of Relativity — A terse dose of insight on the subject.
- On the Electrodynamics of Moving Bodies
- Special Relativity Simulator
- A Relativity Tutorial at Caltech — A basic introduction to concepts of Special and General Relativity, as well as astrophysics.
- Relativity Gravity and Cosmology — A short course offered at MIT.
- Relativity in film clips and animations from the University of New South Wales.
