Albert Einstein's equation E=mc² is among the best-known equations of all time. The equation describes the relation between energy and mass: Portrait of Albert Einstein taken by Yousuf Karsh on February 11, 1948 Albert Einstein (March 14, 1879 – April 18, 1955) was a theoretical physicist who is widely regarded as the greatest scientist of the 20th century. ... In mathematics, one often (not quite always) distinguishes between an identity, which is an assertion that two expressions are equal regardless of the values of any variables that occur within them, and an equation, which may be true for only some (or none) of the values of any such variables. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ...

For a technical account of the equation, see relativistic mass. The term mass in special relativity is used in a couple of different ways, occasionally leading to a great deal of confusion. ...

According to the equation, the total amount of energy obtainable from an object is equivalent to the mass of the object multiplied by the square of the speed of light. Cherenkov effect in a swimming pool nuclear reactor. ...

It is important to note that practical conversions of mass to energy are seldom 100 percent efficient. One theoretically perfect conversion would result from a collision of matter and antimatter; for most cases, byproducts are produced instead of energy, and therefore very little mass is actually converted. In Einstein's equation, mass is energy, but for the sake of clarity, the word converted is used. Matter is anything that has mass and occupies space. ... Antimatter is matter that is composed of the antiparticles of those that constitute normal matter. ...

It is often cited that the equation explains how much energy is given off by the nuclear reactions in a nuclear weapon. This is true in a sense: the energy derived is the difference between the binding energies of the fuel and the fusion or fission products. The mass which is converted into energy is not the fissionable material itself (i.e. the uranium or the plutonium), but related to the strong nuclear force of the bonds which holds the large nucleus together. In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce products different to the initial products. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the epicenter. ... Binding energy is the energy required to disassemble a whole into separate parts. ... The deuterium-tritium fusion reaction is considered the most promising for producing fusion power. ... Sketch of induced nuclear fission, a neutron (n) strikes a uranium nucleus which splits into similar products (F. P.), and releases more neutrons to continue the process, and energy in the form of gamma and other radiation. ... General Name, Symbol, Number Uranium, U, 92 Chemical series Actinides Period, Block 7 , f Density, Hardness 19050 kg/m3, ND Appearance silvery-white metal Atomic properties Atomic weight 238. ... General Name, Symbol, Number Plutonium, Pu, 94 Chemical series Actinides Period, Block 7 , f Density, Hardness 19816 kg/m3, no data Appearance silvery white metal Atomic properties Atomic weight 244. ... The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ...

The equation also proves one of the fundamental limiting factors of space travel - the inability for anything with mass to exceed (or even reach) the speed of light. As the speed of light squared is always constant, the two variables in the equation are energy on one side, and mass on the other.

Therefore, when energy (in this case velocity) increases, mass must increase. Conversely, the more mass an object has, the more energy it requires to accelerate even further. The speed of light (c = 299,792,458 meters per second) is the point where the energy required to reach it is infinite, and attaining such a speed becomes impossible.

It is a little known piece of trivia that Einstein originally wrote the equation in the form m = L/c² (with an "L", instead of an "E", representing energy).

A kilogram of mass completely converts into

• 89,875,517,873,681,764 joules or
• 24,965,421,632 kilowatt-hours or
• 21.48076431 megatons of TNT

See: Mass, momentum, and energy The joule (symbol J, also called newton metre, or coulomb volt) is the SI unit of energy and work. ... The kilowatt-hour (symbol: kW·h) is a unit for measuring energy. ... A megaton or megatonne is a unit of mass equal to 1,000,000 metric tons, i. ... TNT is a three-letter abbreviation with multiple meanings, including: Trinitrotoluene, a chemical explosive. ... Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. ...