Mass–energy equivalence

In <a href="/facts/Physics/a7aH2y08">physics</a>, mass–energy equivalence is the relationship between <a href="/facts/Mass/HHdc8XmF">mass</a> and <a href="/facts/Energy/wd8PrQM7">energy</a> in a system's <a href="/facts/Rest_frame/gFkIWgXk">rest frame</a>. The two differ only by a multiplicative constant and the units of measurement. The principle is described by the physicist <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a>'s formula: E = m c 2 {\displaystyle E=mc^{2}}
. In a <a href="/facts/Reference_frame/15yYfB9M">reference frame</a> where the system is moving, its <a href="/facts/Relativistic_energy/HPXngJQF">relativistic energy</a> and <a href="/facts/Mass_in_special_relativity/aRloR0nW">relativistic mass</a> (instead of <a href="/facts/Rest_Mass/aRloR0nW">rest mass</a>) obey the same formula.
The formula defines the energy (E) of a particle in its rest frame as the product of mass (m) with the <a href="/facts/Speed_of_light/sKSQwdNx">speed of light</a> squared (c2). Because the speed of light is a large number in everyday units (approximately 300000 km/s or 186000 mi/s), the formula implies that a small amount of mass corresponds to an enormous amount of energy.
Rest mass, also called <a href="/facts/Invariant_mass/wNGXNBW6">invariant mass</a>, is a fundamental <a href="/facts/Physical_property/ujcMUceW">physical property</a> of <a href="/facts/Matter/osyc04UN">matter</a>, independent of <a href="/facts/Velocity/Q3o1LVDe">velocity</a>. <a href="/facts/Massless_particle/65Xng6Vx">Massless particles</a> such as <a href="/facts/Photon/mFNhAEzA">photons</a> have zero invariant mass, but massless <a href="/facts/Free_particle/Fjbx90yW">free particles</a> have both momentum and energy.
The equivalence principle implies that when mass is lost in <a href="/facts/Chemical_reaction/GpqWlKrz">chemical reactions</a> or <a href="/facts/Nuclear_reaction/202yClUr">nuclear reactions</a>, a corresponding amount of energy will be released. The energy can be released to the environment (outside of the system being considered) as <a href="/facts/Radiant_energy/8QHpm6KY">radiant energy</a>, such as <a href="/facts/Light/jeofpMn4">light</a>, or as <a href="/facts/Thermal_energy/eVaKAC7K">thermal energy</a>. The principle is fundamental to many fields of physics, including <a href="/facts/Nuclear_physics/fzQbt1aF">nuclear</a> and <a href="/facts/Particle_physics/YgIuyj2t">particle physics</a>.
Mass–energy equivalence arose from <a href="/facts/Special_relativity/vsFFc63E">special relativity</a> as a <a href="/facts/Paradox/3VLGjuWf">paradox</a> described by the French <a href="/facts/Polymath/eqIfjQRu">polymath</a> <a href="/facts/Henri_Poincar%25C3%25A9/AazL2j4X">Henri Poincaré</a> (1854–1912). Einstein was the first to propose the equivalence of mass and energy as a general principle and a consequence of the <a href="/facts/Spacetime_symmetries/q4v9Udnv">symmetries of space and time</a>. The principle first appeared in "Does the inertia of a body depend upon its energy-content?", one of his <a href="/facts/Annus_mirabilis_papers/8LhL5hm7">annus mirabilis papers</a>, published on 21 November 1905. The formula and its relationship to momentum, as described by the <a href="/facts/Energy%25E2%2580%2593momentum_relation/HPXngJQF">energy–momentum relation</a>, were later developed by other physicists.

Mass–energy equivalence open-in-new

Mass–energy equivalence