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In physics, mass–energy equivalence is a concept formulated by Albert Einstein that explains the relationship between mass and energy. It states every mass has an energy equivalent and vice versa—expressed using the formula :: where ''E'' is the energy of a physical system, ''m'' is the mass of the system, and ''c'' is the speed of light in a vacuum (about m/s). In words, energy equals mass multiplied by the speed of light squared. Because the speed of light is a very large number in everyday units, the formula implies that any small amount of matter contains a very large amount of energy. Some of this energy may be released as heat and light by nuclear transformations. This also serves to convert to , no matter what system of measurement units used. Mass–energy equivalence arose originally from special relativity as a paradox described by Henri Poincaré.〔. See also the (English translation )〕 Einstein proposed it in 1905, in the paper ''Does the inertia of a body depend upon its energy-content?'', one of his Annus Mirabilis ("Miraculous Year") Papers.〔. See also the (English translation. )〕 Einstein was the first to propose that the equivalence of mass and energy is a general principle and a consequence of the symmetries of space and time. A consequence of the mass–energy equivalence is that if a body is stationary, it still has some internal or intrinsic energy, called its rest energy. Rest mass and rest energy are equivalent and remain proportional to one another. When the body is in motion (relative to an observer), its total energy is greater than its rest energy. The rest mass (or rest energy) remains an important quantity in this case because it remains the same regardless of this motion, even for the extreme speeds or gravity considered in special and general relativity; thus it is also called the invariant mass. ==Nomenclature== The formula was initially written in many different notations, and its interpretation and justification was further developed in several steps.〔 * In "''Does the inertia of a body depend upon its energy content?''" (1905), Einstein used ''V'' to mean the speed of light in a vacuum and ''L'' to mean the energy lost by a body in the form of radiation.〔 Consequently, the equation was not originally written as a formula but as a sentence in German saying that ''if a body gives off the energy ''L'' in the form of radiation, its mass diminishes by ''L''/''V''2''. A remark placed above it informed that the equation was approximated by neglecting "magnitudes of fourth and higher orders" of a series expansion.〔See the sentence on the last page (p. 641) of the original German edition, above the equation . See also the sentence above the last equation in the English translation, , and the comment on the symbols used in ''About this edition'' that follows the translation.〕 * In May 1907, Einstein explained that the expression for energy ''ε'' of a moving mass point assumes the simplest form, when its expression for the state of rest is chosen to be (where ''μ'' is the mass), which is in agreement with the "principle of the equivalence of mass and energy". In addition, Einstein used the formula , with being the energy of a system of mass points to describe the energy and mass increase of that system when the velocity of the differently moving mass points is increased. * In June 1907, Max Planck rewrote Einstein's mass–energy relationship as , where ''p'' is the pressure and ''V'' the volume to express the relation between mass, its ''latent energy'', and thermodynamic energy within the body.〔 :English Wikisource translation: On the Dynamics of Moving Systems〕 Subsequently in October 1907, this was rewritten as and given a quantum interpretation by Johannes Stark, who assumed its validity and correctness (''Gültigkeit''). * In December 1907, Einstein expressed the equivalence in the form and concluded: ''A mass μ is equivalent, as regards inertia, to a quantity of energy μc2.'' () ''It appears far more natural to consider every inertial mass as a store of energy.'' * In 1909, Gilbert N. Lewis and Richard C. Tolman used two variations of the formula: and , with being the energy of a moving body, its rest energy, the relativistic mass, and the invariant mass. The same relations in different notation were used by Hendrik Lorentz in 1913 (published 1914), though he placed the energy on the left-hand side: and , with being the total energy (rest energy plus kinetic energy) of a moving material point, its rest energy, the relativistic mass, and the invariant (or rest) mass. * In 1911, Max von Laue gave a more comprehensive proof of from the stress–energy tensor,〔 :English Wikisource translation: On the Dynamics of the Theory of Relativity〕 which was later (1918) generalized by Felix Klein. * Einstein returned to the topic once again after World War II and this time he wrote in the title of his article〔A.Einstein '': the most urgent problem of our time'' Science illustrated, vol. 1 no. 1, April issue, pp. 16–17, 1946 (item 417 in the "Bibliography"〕 intended as an explanation for a general reader by analogy.〔M.C.Shields ''Bibliography of the Writings of Albert Einstein to May 1951'' in Albert Einstein: Philosopher-Scientist by Paul Arthur Schilpp (Editor) (Albert Einstein Philosopher – Scientist )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mass–energy equivalence」の詳細全文を読む スポンサード リンク
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