Relativity

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In our time, there has been unloosed a cataclysm which has swept away space, time, and matter hitherto regarded as the firmest pillars of natural science, but only to make place for a view of things of wider scope, and entailing a deeper vision. — Hermann Weyl, Space, Time, Matter

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Introduction¹

Hard Stuff Made Easy: Physics (LondonCityGirl, YouTube Playlist)

Dictionary

relativity : 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 — Webster See also OneLook

Thesaurus

Roget’s II (Thesaurus.com), Merriam-Webster Thesaurus, Visuwords

Encyclopedia

Relativity, generally refers to the theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity.

Special relativity applies to elementary particles and their interactions, describing all their physical phenomena except gravity.

General relativity explains the law of gravitation and its relation to other forces of nature. It applies to the cosmological and astrophysical realm, including astronomy.

The theory transformed theoretical physics and astronomy during the 20th century, superseding a 200-year-old theory of mechanics created primarily by Isaac Newton. It introduced concepts including spacetime as a unified entity of space and time, relativity of simultaneity, kinematic and gravitational time dilation, and length contraction. — Wikipedia

Relativity (Encyclopædia Britannica)

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Relativity (WolframAlpha)

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Foundation

Theory

Relativity: The Special and General Theory (Albert Einstein, Bartleby.com)
Relativity: The Special and General Theory (Albert Einstein, WorldCat)
Relativity: The Special and the General Theory (Wikipedia)

What is Relativity? Einstein’s Mind-Bending Theory Explained (Dan Falk, Mach, NBC News)
The Theory of Relativity (Ask an Astronomer, Cornell University)

Relativity (Fermilab, YouTube Playlist)

Relativity (Eric Weisstein’s World of Physics, Wolfram Research)

Special relativity is a scientific theory regarding the relationship between space and time. In Albert Einstein’s original treatment, the theory is based on two postulates:
1. The laws of physics are invariant (that is, identical) in all inertial frames of reference (that is, frames of reference with no acceleration).
2. The speed of light in vacuum is the same for all observers, regardless of the motion of the light source or observer. — Wikipedia

Special Relativity (Eric Weisstein’s World of Physics, Wolfram Research)

General relativity is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton’s law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations. — Wikipedia

General Relativity (Eric Weisstein’s World of Physics, Wolfram Research)

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