Supplementary file 1_Symmetry, law invariance, and the physical admissibility of internal time.pdf

The pacemaker–accumulator model has long dominated theories of internal time, yet it remains structurally disconnected from the physical principles that define time in the external world. In physics, time is not generated by an autonomous mechanism but operationally constructed from regular processes governed by invariant laws. Temporal admissibility depends on symmetry, local equivalence, and reproducibility across physical implementations—not on the existence of an internally generated pulse stream. By contrast, prevailing models of internal timing posit a self-contained mechanism whose linkage to shared physical parameters is left unspecified, thereby separating internal temporal organization from the conditions that legitimize time in physics. We argue that this separation is conceptually untenable. Any viable account of internal time must satisfy the same law-based criteria that govern physical clocks. Under sustained gravito-inertial loading, regular otolith afferents converge to stable tonic firing in a steady-state regime. This regularity reflects the steady-state output of sensory transduction under constant gravito-inertial input, rather than the presence of a self-sustained oscillator. Internal time, on this view, is not produced but referenced. Grounded in symmetry, local equivalence, and relational informational accessibility, vestibular dynamics provide a physically admissible sensory reference against which events are compared, restoring continuity between internal temporal organization and the operational foundations of physical time.