The spacetime manifold, the stage on which physics is played, is constructed ab initio in a formal program that resembles the logicist reconstruction of mathematics. Zermelo’s set theory extended by urelemente serves as a framework, to which physically interpretable proper axioms are added. From this basis, a topology and subsequently a Hausdorff manifold are readily constructed which bear the properties of the known spacetime manifold. The present approach takes worldlines rather than spacetime points to be primitive, having them represented by (...) urelemente. Thereby it is demonstrated that an important part of physics is formally reducible to set theory. (shrink)

An ab-initio foundation for relativistic spacetime is given, which is a conservative extension of Zermelo’s set theory with urelemente. Primitive entities are worldlines rather than spacetime points. Spacetime points are sets of intersecting worldlines. By the proper axioms, they form a manifold. Entities known in differential geometry, up to a metric, are defined and have the usual properties. A set-realistic point of view is adopted. The intended ontology is a set-theoretical hierarchy with a broad base of the empty set and (...) urelemente. Sets generated from the empty set are mathematically interpreted, all other sets are physically interpreted. (shrink)

Quasi-set theory by S. French and D. Krause has been so far the most promising attempt of a formal theory of non-individuals. However, due to its sharp bivalent truth valuations, maximally fine-grained binary relations are readily found, in which members of equivalence classes are substitutable for each other in formulas salva veritate. Hence its mentioning and non-mentioning of individuals differs from existing set theory with defined identity merely by the range of nominal definitions. On a semantic level, quasi-set theory does (...) not provide an interpretation with explanatory power of its language terms as non-individuals, and it is not easy to see how such an interpretation can be set up. (shrink)