special theory of relativity

noun Physics.



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Also called special relativity.

Origin of special theory of relativity

First recorded in 1915–20

Definition for special relativity (2 of 2)

[ rel-uh-tiv-i-tee ]
/ ˌrɛl əˈtɪv ɪ ti /


the state or fact of being relative.
Physics. a theory, formulated essentially by Albert Einstein, that all motion must be defined relative to a frame of reference and that space and time are relative, rather than absolute concepts: it consists of two principal parts. The theory dealing with uniform motion (special theory of relativity or special relativity) is based on the two postulates that physical laws have the same mathematical form when expressed in any inertial system, and the velocity of light is independent of the motion of its source and will have the same value when measured by observers moving with constant velocity with respect to each other. Derivable from these postulates are the conclusions that there can be no motion at a speed greater than that of light in a vacuum, mass increases as velocity increases, mass and energy are equivalent, and time is dependent on the relative motion of an observer measuring the time. The theory dealing with gravity (general theory of relativity or general relativity) is based on the postulate that the local effects of a gravitational field and of acceleration of an inertial system are identical.
dependence of a mental state or process upon the nature of the human mind: relativity of values; relativity of knowledge.

Origin of relativity

First recorded in 1825–35; relative + -ity


non·rel·a·tiv·i·ty, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

British Dictionary definitions for special relativity (1 of 2)

/ (ˌrɛləˈtɪvɪtɪ) /


either of two theories developed by Albert Einstein, the special theory of relativity, which requires that the laws of physics shall be the same as seen by any two different observers in uniform relative motion, and the general theory of relativity which considers observers with relative acceleration and leads to a theory of gravitation
philosophy dependence upon some variable factor such as the psychological, social, or environmental contextSee relativism
the state or quality of being relative

British Dictionary definitions for special relativity (2 of 2)

special theory of relativity


the theory proposed in 1905 by Einstein, which assumes that the laws of physics are equally valid in all nonaccelerated frames of reference and that the speed of electromagnetic radiation in free space has the same value for all inertial observers. It leads to the idea of a space-time continuum and the equivalence of mass and energy. In combination with quantum mechanics it forms the basis of the theory of elementary particlesAlso called: special relativity See also general theory of relativity
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for special relativity (1 of 2)

Special Relativity
[ spĕshəl ]

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 v1 observes another faster object (such as a rocket fired from the spacecraft) moving ahead of it in the same direction with velocity v2, an observer at rest observes the faster object moving at velocity that is not just the sum of v1 and v2, but at the slower speed v1 + v21 + v1v2c2. See also General Relativity time dilation.

Scientific definitions for special relativity (2 of 2)

[ rĕl′ə-tĭvĭ-tē ]

Either of two theories in physics developed by Albert Einstein, General Relativity or Special Relativity. See Notes at Einstein gravity space-time.

Other words from relativity

relativistic adjective
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for special relativity


notes for relativity

The special and general theories of relativity have had important implications for thought in general. They show that no frame of reference for observation of nature is more correct than any other.

notes for relativity

It is important to distinguish between the theory of relativity, in which the laws of nature are the same for all observers anywhere in the universe, and the philosophical doctrine of relativism, which holds that there are no absolute truths. The similarity in their names has been a source of confusion.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.