# 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.

• 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

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.
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.