Temporal Measurement and SI Instantiation: Why the Problem of Time Persists Across Physical Theories

Physical measurement practice is governed by a tacit but robust norm: a quantity is ordinarily taken to be measured only if the measurement interaction instantiates that quantity’s own physical dimension. While indirect and theory-laden measurement is widespread in physics, dimensional instantiation is typically preserved across measurement chains. This paper argues that temporal measurement is exceptional with respect to this norm. Across contemporary physical theories, what is operationally designated as time is supplied through the instantiation of non-temporal SI quantities—such as length, frequency, energy, entropy, or dimensionless ratios—rather than through any interaction that instantiates time itself. By examining this substitution systematically, the paper identifies a domain-general measurement norm and shows how time uniquely violates it within standard physical practice. A worked exemplar from general relativity illustrates the point: proper time is operationally obtained via spacetime arc-length, instantiating length rather than a temporal magnitude. Because different theories operationalize time by instantiating different physical dimensions, temporal quantities lack cross-theory measurement continuity. The paper offers a diagnostic account of why temporal unification problems persist across physical theories, without advancing metaphysical or reformist proposals concerning the nature of time. This paper forms part of a broader investigation into the measurement and representation of time in physical theory.