relativity

noun

rel·​a·​tiv·​i·​ty ˌre-lə-ˈti-və-tē 

plural relativities

1

a

: the quality or state of being relative

b

: something that is relative

2

: the state of being dependent for existence on or determined in nature, value, or quality by relation to something else

3

a

: a theory which is based on the two postulates (1) that the speed of light in a vacuum is constant and independent of the source or observer and (2) that the mathematical forms of the laws of physics are invariant in all inertial systems and which leads to the assertion of the equivalence of mass and energy and of change in mass, dimension, and time with increased velocity

called also special relativity, special theory of relativity

b

: an extension of the theory to include gravitation and related acceleration phenomena

called also general relativity, general theory of relativity

4

: relativism sense 1b

Example Sentences

Recent Examples on the Web

With fellow physicist Roger Penrose, Hawking merged Einstein's theory of relativity with quantum theory to suggest that space and time would begin with the Big Bang and end in black holes. —Emma Tucker, CNN, 8 Jan. 2022

These bright flashes are from a planet and its star bending the light of a more distant star, magnifying it according to Einstein’s rules for relativity. —Briley Lewis, Popular Science, 18 Apr. 2023

Einstein biography and his own familial connection to the father of relativity. —Manuel Mendoza, Dallas News, 10 Sep. 2020

Another issue is relativity. —Alison Omens, Fortune, 31 Oct. 2020

With Einstein and relativity, a big insight is that space and time don’t really exist as separate entities so much as there’s this one thing called the space-time continuum. —Quanta Magazine, 29 Mar. 2023

Of course, this would be a one-way trip, and humans can’t yet (or possibly ever) make a ship that approaches light-speed, but never mind — relativity still says this form of time travel is possible. —Stephen C. George, Discover Magazine, 27 Mar. 2023

His working theory is based on Albert Einstein’s relativity discussion. —Tim Newcomb, Popular Mechanics, 2 Mar. 2023

Maskawa showed that for most processes time-reversal symmetry follows unavoidably from three other, deeper principles—relativity, quantum mechanics and the high symmetry that is central to our theories of the universe’s four fundamental forces. —Frank Wilczek, WSJ, 17 Nov. 2022

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Word History

First Known Use

circa 1834, in the meaning defined at sense 1a

Phrases Containing relativity

• general theory of relativity
• special relativity
• general relativity
• special theory of relativity

• general theory of relativity
• special relativity
• general relativity
• special theory of relativity

Kids Definition

relativity

noun

rel·​a·​tiv·​i·​ty ˌrel-ə-ˈtiv-ət-ē 

plural relativities

1

: the quality or state of being relative

especially : dependence on something else

2

a

: a theory in physics that considers mass and energy to be equal and that states that a moving object will experience changes in mass, size, and time which are related to its speed and are not noticeable except at speeds approaching that of light

b

: an extension of relativity theory to include gravity and its related acceleration effects