I'm sure each of you is well-versed in the first law of thermodynamics: energy cannot be created or destroyed. Thus, there is the law conservation of energy. E=mc^2 states that energy and mass are functions of each other, basically one and the same less a conversion factor. I take mass to be rest energy. Matter can be created from photon collisions, and particles can be anhillated by collision as well, thus establishing that there is no law of conservation of mass. I have heard that photons do have energy but do not have mass. I don't see how this is possible based on E=mc^2. E would =0 if m=0, and m=0 if E=0. I would greatly appreciate it if someone would clarify why there is a law of conservation of energy but not of mass if the two are one and the same. (Pardon my rudimentary knowledge..I'm in high school and have yet to take a physics class.) I have taken calculus, so mathematical explanations of a light degree will be understood.