Mach Energy is a source of energy based on Mach’s principle; in particular it is based on Einstein’s interpretation of Mach’s principle. In a single particle universe the particle’s mass can’t be measured, and other things can’t be measured such as time. As a consequence the conservation of energy may not hold in a single particle universe. The vast empty regions of our universe may have some of the properties of the single particle universe. Is this the source of dark energy? From a Mach’s principle standpoint the source of reality is particles, say light. Does conventional physics hold in the regions of space that are unlit and free of any particles? In the beginning was there light?