Einstein's famous equation equating energy with mass, revealing that mass is a form of energy, is an elegant and tremendously useful equation. However, when drilled down to the fine-grain level all the terms of the equation are largely undefined. The speed of light is listed as a constant without a very clear reason why it is that velocity and how that is involved in relating mass and energy. Energy is the capacity to do work, but what is it physically and what is the source of energy in the uni