 However, for Rindler, there is nothing within special relativity itself that rules out the possibility that there exists fundamental, structureless particles (i.e., particles that are “atomic” in the philosophical sense of the term). If such particles exist, it is possible according to Einstein’s equation that some or all of the mass of such particles “disappears” and an equivalent amount of energy “appears” within the relevant physical system. Thus, Rindler seems to be suggesting that we should confine our interpretation of mass-energy equivalence to what we can deduce from special relativity. Thus, we should hold that Einstein’s equation at least allows for genuine conversions of mass into energy, in the sense that there may be cases where a certain amount of inertial mass “disappears” from within a physical system and a corresponding amount of energy “appears.” Furthermore, in such cases we cannot explain the reaction as merely involving a transformation of one kind of energy into another.