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'''E=mc&sup2;''' is perhaps the most famous, most immediately recognizable to the public, most widely quoted by the public, and least understood by the public, of all equations in science.  Most people recognize it instantly, but when asked to explain it, might say something like ''"It says that matter and energy are the same/equivalent"'', or ''"It explains relativity"'', or ''"It tells where nuclear power comes from"'', or ''"It's about atomic bombs."''  <!-- In this article, we will attempt to explain what it really is, and what it isn't.-->

The equation is about the physical concepts of [[mass (science)|mass]] and [[energy]].

Mass refers to what is often called ''inertia'' (though that term is used much less now than it was 100 years ago).  It is sometimes called ''inertial mass''.  Inertial mass is the resistance of an object to being accelerated when a force is applied.  The ''m'' in ''E=mc&sup2;'' is the same as the ''m'' in [[Newton]]'s formula of motion ''F=ma''.  Gravitational mass is what makes things ''heavy'', that is, what is acted upon by gravity.  It is the ''m<sub>1</sub>'' and ''m<sub>2</sub>'' in Newton's formula for gravity <math>F = \frac{Gm_1m_2}{d^2}</math>.  The difference between inertial mass and gravitational mass used to be a burning issue among physicists, eventually being tested, and found to be the same, by the famous [[Eotvos experiment]]s.  (Note that general relativity does have an explanation for why this should be, but this is not relevant here.)

Energy refers to kinetic energy of motion, or radiated energy.

*''E=mc&sup2;'' is not about gravity or gravitational mass.
*''E=mc&sup2;'' is not about light, or other electromagnetic radiation, except insofar as it is a form of energy.
*''E=mc&sup2;'' is not about nuclear power ''per se''.  It applies everywhere.
*''E=mc&sup2;'' is not about where the power of the atomic bomb comes from, though the physicists developing atomic power and atomic bombs were completely familiar with it.

A little calculation will show that ''E=mc&sup2;'' is dimensionally correct.  So, for example, in [[SI]] units (also called MKS units), E is in [[Joule]]s, m in [[kilogram]]s, and c in [[meter]]s per second.  In [[CGS]] units or  units of the [[US Customary System of Units|US Customary System]] ([[pound]]s and [[foot|feet]]) it is also dimensionally correct, as long as the units are used consistently.  <ref>Physicists, when they are really into theory, sometimes like to use "natural units", which are calibrated so that ''c'' is dimensionless and has the value 1. That is not the approach taken here, however.</ref>

In any normal units, the value of c, the speed of light, is enormous, its square even more so.  This means that ''E=mc&sup2;'' equates an extremely tiny amount of mass with an extremely large amount of energy.  This gives the equation some of its mystique.  <!--We will attempt to dispel that mystique, and explain just what the equation means.-->



''E=mc&sup2;'' is a meaningless though working, almost nonsensical though often applied, e.g., in nuclear physics, statement that purports to relate all matter to energy and light.<ref>The equation claims that the total energy ''E'' of a body in all forms is equal to that body's mass ''m'' multiplied by the square of the speed of light ''c''. </ref>  In fact, no theory has successfully unified the laws governing mass (''i.e.'', gravity) with the laws governing light (''i.e.'', electromagnetism).  Simply put, ''E=mc&sup2;'' is [[liberal]] claptrap.

[[Biblical Scientific Foreknowledge]] predicts that a unified theory of all the laws of physics is impossible, because light and matter were created at different times, in different ways, as described in the [[Book of Genesis]].

[[Mass]] is a measure of an object's inertia, and is directly related to the force of [[gravity]].  In contrast, the intrinsic [[energy]] of an object (such as an [[atom]]) is a function of electrostatic charge and other non-inertial forces, having nothing to do with gravity.  Declaring the object's energy to be a function of inertia rather than electrostatics is an absurd and impossible attempt to unify the forces of nature, contrary to [[Biblical Scientific Foreknowledge]].

For more than a century, the claim that ''E=mc&sup2;'' has never yielded anything of value.  Often it seems to be used as a redefinition of &quot;[[energy]]&quot; for pseudo-scientific purposes, as by the [[lamestream media]]. There have been attempts to find some justification for the equation in already understood processes involved in [[nuclear power]] generation and [[nuclear weapon]]s, and in the speculation about [[antimatter]].<ref>[http://www.pbs.org/wgbh/nova/physics/legacy-of-e-equals-mc2.html Peter Tyson ''The Legacy of E=mc&sup2;''] October 11, 2005. PBS ''NOVA''. </ref> The energy released in matter/antimatter annihilations corresponds to ''E=mc&sup2;'' for example the annihilation of an electron and a positron (each with rest energy of 0.511 mega electron volts according to ''E=mc&sup2;'') results in the release of two [[gamma ray]] [[photon]]s, which each have energy 0.511 mega electron volts.<ref>[http://www.lbl.gov/abc/Antimatter.html Lawrence Berkeley National Laboratory] ''The ABC of Nuclear Science''</ref>

The [[Theory of Relativity]] has never been able to mathematically derive ''E=mc&sup2;'' from first principles, and a physicist observed in a peer-reviewed paper published in 2011 that "Leaving aside that it continues to be affirmed experimentally, a rigorous proof of the mass-energy equivalence is probably beyond the purview of the special theory."<ref>[http://adsabs.harvard.edu/abs/2011AmJPh..79..591H Eugene Hecht: ''How Einstein confirmed E<sub>0</sub>=mc&sup2;''], American Journal of Physics, Volume 79, Issue 6, pp. 591-600 (2011)</ref>

It has been known for a long time that radiation has a mass equivalence, which was correctly derived by [[Henri Poincare]] in 1904,<ref>[http://www.opticsinfobase.org/josa/abstract.cfm?uri=josa-42-8-540  Herbert E. Ives ''Derivation of the Mass-Energy Relation''], JOSA, Vol. 42, Issue 8, pp. 540-543 (1952)</ref> but the equation ''E=mc&sup2;'' makes a claim far beyond that limited circumstance:

{{cquote|The equality of the mass equivalent of radiation to the mass lost by a radiating body is derivable from Poincaré’s momentum of radiation (1900) and his principle of relativity (1904).|||Herbert Ives, 1952}}