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Mass–energy equivalence arose from special relativity as a paradox described by the French polymath Henri Poincaré (1854–1912). [4] Einstein was the first to propose the equivalence of mass and energy as a general principle and a consequence of the symmetries of space and time.
In physics, the energy–momentum relation, or relativistic dispersion relation, is the relativistic equation relating total energy (which is also called relativistic energy) to invariant mass (which is also called rest mass) and momentum. It is the extension of mass–energy equivalence for bodies or systems with non-zero momentum.
Einstein demonstrated that Poincaré's artifice was superfluous. Rather, he argued that mass-energy equivalence was a necessary and sufficient condition to resolve the paradox. In his demonstration, Einstein provided a derivation of mass-energy equivalence that was distinct from his original derivation.
Because of the relativistic equivalence between mass and energy, the eV is also sometimes used as a unit of mass. The Hartree (the atomic unit of energy) is commonly used in the field of computational chemistry since such units arise directly from the calculation algorithms without any need for conversion.
According to the concept of mass–energy equivalence, invariant mass is equivalent to rest energy, while relativistic mass is equivalent to relativistic energy (also called total energy). The term "relativistic mass" tends not to be used in particle and nuclear physics and is often avoided by writers on special relativity, in favor of ...
The mass of a body is a measure of its energy-content; if the energy changes by L, the mass changes in the same sense by L/(9 × 10 20), the energy being measured in ergs, and the mass in grammes. If the theory corresponds to the facts, radiation conveys inertia between the emitting and absorbing bodies.
The law of conservation of mass and the analogous law of conservation of energy were finally generalized and unified into the principle of mass–energy equivalence, described by Albert Einstein's equation =. Special relativity also redefines the concept of mass and energy, which can be used interchangeably and are defined relative to the frame ...
Mass–energy equivalence also holds in macroscopic systems. [35] For example, if one takes exactly one kilogram of ice, and applies heat, the mass of the resulting melt-water will be more than a kilogram: it will include the mass from the thermal energy (latent heat) used to melt the ice; this follows from the conservation of energy. [36]