Abstract

This dissertation elucidates the notion of physical system which opens new conceptual pathways that connect the three realms of physical theory; spacetime, material bodies and their properties, and the laws of nature which govern their evolution. The notion of physical system includes two presuppositions regarding their structure. The first presupposition is a description of isolated systems and their evolution in time, which amounts to a Paradigm of Uniform Motion. The second presupposition describes how parts of a physical system are combined into wholes. This presupposition amounts to a Rule of Composition. Once we make these presuppositions explicit we can derive the spacetime structures and the fundamental equations of motion. "Newtonian" and "relativistic" systems are shown to differ with respect to the paradigm of uniform motion, a difference that leads to the respective structures of Newtonian mechanics and the Special Theory of Relativity. ;The philosophical framework offered in this dissertation provides a new interpretation of the concept of mass, and a new elucidation of the relation between the conservations of mass and momentum. Previous analyses of the concept have claimed that "mass" cannot be defined and broken down to more primitive predicates. The framework offered here, on the other hand, enables the systematic reduction of the concept of mass to motions and the presuppositions we have regarding the nature of physical systems. The new interpretation of mass reveals a surprising connection between mass and inertial reference frames, as they are both shown to be derived, in a similar way, from our definition of physical systems. Mass is by necessity attributed to bodies in virtue of the frame we use to describe their motions. This account also enables us to understand the different conceptual roles of mass and their interconnections. In the context of Newtonian mechanics, the roles of mass as a Quantity of Matter, as the Inertial property of bodies, and as Gravitational mass are shown to be various aspects of a single role the concept has in the new framework offered here. In the context of the Special Theory of Relativity, rest mass and relativistic mass are similarly analyzed as consequences of our presuppositions regarding physical systems