The
invariant speed or observer invariant speed is a speed which is measured to be the same in all
reference frames
In physics and astronomy, a frame of reference (or reference frame) is an abstract coordinate system whose origin, orientation, and scale are specified by a set of reference points― geometric points whose position is identified both mathem ...
by all observers. The invariance of the
speed of light
The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit fo ...
is one of the
postulates of special relativity In physics, Albert Einstein's 1905 theory of special relativity is derived from first principles now called the postulates of special relativity. Einstein's formulation only uses two postulates, though his derivation implies a few more assumptions ...
, and the terms ''speed of light'' and ''invariant speed'' are often considered synonymous. In non-relativistic
classical mechanics
Classical mechanics is a physical theory describing the motion of macroscopic objects, from projectiles to parts of machinery, and astronomical objects, such as spacecraft, planets, stars, and galaxies. For objects governed by classical ...
, or Newtonian mechanics, finite invariant speed does not exist (the only invariant speed predicted by Newtonian mechanics is infinity).
See also
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Variable speed of light
A variable speed of light (VSL) is a feature of a family of hypotheses stating that the speed of light may in some way not be constant, for example, that it varies in space or time, or depending on frequency. Accepted classical theories of phy ...
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Red Queen's race
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Minkowski diagram
A spacetime diagram is a graphical illustration of the properties of space and time in the special theory of relativity. Spacetime diagrams allow a qualitative understanding of the corresponding phenomena like time dilation and length contracti ...
*
Speed of gravity
In classical theories of gravitation, the changes in a gravitational field propagate. A change in the distribution of energy and momentum of matter results in subsequent alteration, at a distance, of the gravitational field which it produces. I ...
References
Theory of relativity
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