You don't know, nuclear fission and fusion are philosophically opposite reaction, right? For example, meeting and departing are the same? You know only energy. Do you know energy is a macroscopic concept? Your people reversely interprets the natural law like that way? If a reaction is exothermic there must occur a mass loss. Nonsense! We know when particle physicists encounter a logical crises they hide themselves behind this energy shadow, under the name of quantitative calculation, done based on a stupid non-scientific postulation. newedana