The empirical success of relativity is among the most firmly established achievements of modern physics. Experimental observations involving frequency shifts, clock behavior, signal propagation, and gravitational phenomena are routinely interpreted within relativistic frameworks based on spacetime geometry. The extent to which such observations uniquely determine the formalism, theory, and ontology commonly associated with relativity, however, remains a distinct methodological question. This article examines the relationship between observation, formalism, theory, and ontology in the context of relativity. A distinction is drawn between local measurement outcomes, empirical relations, theoretical postulates, mathematical formalisms, and ontological interpretations. Particular attention is devoted to the role of additional assumptions employed in the standard construction of relativistic formalism and to the problem of underdetermination. The analysis identifies three levels of underdetermination: the underdetermination of formalism by observation, the underdetermination of theory by formalism, and the underdetermination of ontology by theory. Together, these levels form a hierarchy of underdetermination that extends the traditional discussion of theory underdetermination in the philosophy of science. The article further argues that the empirical success of relativity does not by itself establish the ontological necessity of spacetime. As a methodological illustration, the Theory of Absolute (ToA) is presented as an example of an alternative framework based on a different interpretation of Einstein’s postulates and not requiring spacetime as a fundamental ontological entity. The central conclusion is that empirical observations constrain physical descriptions of nature, but do not uniquely determine either formalism, theory, or ontology. Consequently, the transition from observation to spacetime ontology involves additional mathematical, theoretical, and interpretative assumptions beyond the empirical data themselves.
Adam Marek Behr (Fri,) studied this question.