# Mass-Energy Equivalence Law

(Redirected from Mass–Energy Equivalence)

A Mass-Energy_Equivalence Law is a physical equivalence law that ...

## References

### 2015

• (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/Mass–energy_equivalence Retrieved:2015-4-11.
• In physics, mass–energy equivalence is the concept that the mass of an object or system is a measure of its energy content. For instance, adding 25 kilowatt-hours (90 megajoules) of any form of energy to any object increases its mass by 1 microgram (and, accordingly, its inertia and weight) even though no matter has been added.

A physical system has a property called energy and a corresponding property called mass; the two properties are equivalent in that they are always both present in the same (i.e. constant) proportion to one another. Mass–energy equivalence arose originally from special relativity, as developed by Albert Einstein, who proposed this equivalence in 1905 in one of his "Annus Mirabilis" papers entitled "Does the inertia of an object depend upon its energy content?"[1] The equivalence of energy E and mass m is reliant on the speed of light c and is described by the famous equation: :$\displaystyle{ E = mc^2 }$ Thus, the mass–energy relation can be used to relate the rest energy to the rest mass, or to relate the total energy to the total mass. To instead relate the total energy or mass to the rest energy or mass, a generalization of the mass–energy relation is required: the energy–momentum relation.

has frequently been invoked as an explanation for the origin of energy in nuclear processes specifically, but such processes can be understood as converting nuclear potential energy in a manner precisely analogous to the way that chemical processes convert electrical potential energy. The more common association of mass–energy equivalence with nuclear processes derives from the fact that the large amounts of energy released in such reactions may exhibit enough mass that the mass loss (which is called the mass defect) may be measured, when the released energy (and its mass) have been removed from the system; while the energy released in chemical processes is smaller by roughly six orders of magnitude, and so the resulting mass defect is much more difficult to measure. For example, the loss of mass to an atom and a neutron, as a result of the capture of the neutron and the production of a gamma ray, has been used to test mass–energy equivalence to high precision, as the energy of the gamma ray may be compared with the mass defect after capture. In 2005, these were found to agree to 0.0004%, the most precise test of the equivalence of mass and energy to date. This test was performed in the World Year of Physics 2005, a centennial celebration of Albert Einstein's achievements in 1905.[2]

Einstein was not the first to propose a mass–energy relationship (see the History section). However, Einstein was the first scientist to propose the formula and the first to interpret mass–energy equivalence as a fundamental principle that follows from the relativistic symmetries of space and time.