 Lange (2001, 2002) has suggested a rather unique interpretation of mass-energy equivalence. Lange begins his interpretation by arguing that rest-mass is the only real property of physical systems. This claim by itself suggests that there can be no such thing as a physical process by which mass is converted into energy, for as Lange asks “in what sense can mass be converted into energy when mass and energy are not on a par in terms of their reality?” (2002, p. 227, emphasis in original). Lange then goes on to argue that a careful analysis of purported conversions of mass-energy equivalence reveals that there is no physical process by which mass is ever converted into energy. Instead, Lange argues, the apparent conversion of mass into energy (or vice versa) is an illusion that arises when we shift our level of analysis in examining a physical system.