# E=MC^2 and the creation of mass

First of all, if anything in this post is incorrect I'm sorry. My physics is still developing and I hope to learn a lot here!

So, E=MC^2 states that mass can be converted directly in to energy, and a he'll of a lot of it, correct? However, energy cannot be created or destroyed, only distributed, also correct?

So, does this mean mass can not be directly created, or does E=MC^2 simply provide an imbalance of energy that can't be explained? I would like an explanation because this has been bugging me for a while now :).

Thank you everyone, hope you understand what I'm trying to say!

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mathman
E=mc^2 works both ways. Specifically, under the right circumstances mass can be converted from energy. Pair production (gamma ray -> electron positron pair) is the simplest example.

Probably the best way to think about $$E=mc^2$$ is that mass is a form of energy. For example, the mass of an electron is just the energy that an electron has that is not due to its motion or interaction with other objects. The total energy of an object is mass energy + energy of motion (kinetic energy) + energy of interaction (potential energy). In general, if the circumstances are right, any form of energy could be converted into any other form of energy, mass energy included. Total energy is always conserved, but you have to include all types of energy for that to work out.

In case you are wondering the formula for the energy of a moving body is $$E^2 = (mc^2)^2 + (pc)^2$$ where $$p$$ is the momentum of the object. Notice that when $$p=0$$ you get back $$E=mc^2$$. Also notice that when $$m=0$$ (massless particles, e.g. photons) $$E=pc$$. This is the relationship between the energy and momentum of a photon or any other massless particle.

In a typical atomic bomb, we are able to convert only a few percent of the mass but that still yields as huige amount of energy...because in mc2 the factor c is reallyeally big.

On the other hand we are even more deficient in our knolwedge of converting energy into mass...I don't believe we have much of a practical means to do so in all too many practical applications.

So while your physics may be developing as you say, so is mankinds....on the other hand:

(gamma ray -> electron positron pair) is the simplest example.
those particles would quickly annihilate and "disappear" ...and yet we have been able to harness that process for PET scanning...a nuclear medicine imaging technique....see Wikiepdia for details....

Thanks for all the replies, I think I get it out! Definitely going to read more in to the subject however. Thanks again for your help.