# Application of $E = mc^2$ [duplicate]

We very well know that mass-energy equivalence is given by $E = mc^2$. My question however is how would we actually convert an object or some mass into its pure energy state and then if possible even back to its original state. The answer needs to state the requirements for conversion into pure energy. We all know its possible theoretically but how would it be done in a practical world. Just assume that the mechanism required for the process is possible. In short I want the process/mechanism for how to go about it.

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## marked as duplicate by John Rennie, Brandon Enright, Dimensio1n0, David Z♦Jan 27 '14 at 12:30

What do you mean be "pure energy state"? –  David H Jan 27 '14 at 6:53
"Pure energy" makes as much sense as "pure weight". Energy is a property, not a thing in itself. –  Stan Liou Jan 27 '14 at 6:53
possible duplicate of What keeps mass from turning into energy? –  John Rennie Jan 27 '14 at 6:57
rahulgarg12342: the word energy is much abused. Mass doesn't turn into energy, it turns into other particles. Some of these particles may be photons, but photons aren't energy, they are just massless particles. My answer to the question I've suggested as a duplicate goes into this. –  John Rennie Jan 27 '14 at 7:00
The question Can we make usable energy from subnuclear particles? is also relevant. –  John Rennie Jan 27 '14 at 7:51

Very basically there are conservation laws coming from fundamental attributes of the theories we have developed to describe natural phenomena.

Energy is an attribute of matter. Matter is built up by fundamental particles according to the physical laws governing the existence of these particles. There is a hierarchical organization where different frameworks of theory are needed in order to describe and predict the behavior of matter, but still the fundamental conservation laws hold. Elementary particles form protons and neutrons, protons and neutrons form nuclei, nuclei and electrons form atoms and molecules, atoms and molecules form solids liquids gases and plasma.

When studying elementary particles, for example, the $E=mc^2$ condition is dominant to what happens when an electron and a positron collide. The total energy of the collision is distributed among elementary particles . The result of annihilation of the original input is not reversible in any reasonable way, because in many cases one would have to collide many particles in order to build up the original electron and positron. Look at page 5 of this link . to see how complicated annihilation of the two simplest elementary particles is.

When we go one step in complexity, protons colliding on antiprotons, then again the total energy is distributed to many particles when the antiprotons annihilate , but reversibility is unthinkable experimentally. Antiprotons are created in even higher energy collisions at great effort and expense .

Going to the complexity of atom on antiatom a second level of difficulty of the creation of antiatoms enters the game, and from then on, molecules and solids etc, annihilation cannot be done in the lab, because there is no naturally found bulk antimatter and it cannot be created with our technology.

We do use the $E=mc^2$ relation in getting energy from nuclei according to the differences in the binding energy of the nucleons in the nucleus. This is a small part of the energy of the nucleus in each case and certainly not reversible in any sensible way.

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