# Special-relativity meaning

The physical theory of space and time developed by Albert Einstein, based on the postulates that all the laws of physics are equally valid in all frames of reference moving at a uniform velocity and that the speed of light from a uniformly moving source is always the same, regardless of how fast or slow the source or its observer is moving. The theory has as consequences the relativistic mass increase of rapidly moving objects, the Lorentz-FitzGerald contraction, time dilatation, and the principle of mass-energy equivalence.

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The theory of space and time developed by Albert Einstein, based on the postulates that all the laws of physics are equally valid in all reference frames moving at a constant speed relative to each other (that is, in all

**inertial frames**), and that the speed of light is observed to be the same in all reference frames. To compare measurements of length or time made in different inertial frames, their values must be regarded as components of vectors in a 4-dimensional space called**Minkowski space-time**. Different frames are related to each other mathematically by**Lorentz transformations**. Special Relativity predicts that all massless particles, such as photons, are always necessarily moving at the speed of light, while all particles with mass are always necessarily moving slower than the speed of light, and only particles with mass can be at rest. The theory also states that velocities are not simply additive. For example, if an object (such as a spacecraft) moving with velocity v_{1}observes another faster object (such as a rocket fired from the spacecraft) moving ahead of it in the same direction with velocity v_{2}, an observer at rest observes the faster object moving at velocity that is not just the sum of v_{1}and v_{2}, but at the slower speed^{v1 + v2}/_{1 +v1v2/c2}.(physics) A theory that (neglecting the effects of gravity) reconciles the principle of relativity with the observation that the speed of light is constant in all frames of reference.

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