The Arrow of Time as Accumulated Structural Commitment

The origin of the arrow of time remains one of the most persistent conceptual problems in physics. While microscopic laws are largely reversible, the macroscopic universe exhibits unmistakable temporal directionality. This paper proposes that the arrow of time can be understood as the cumulative consequence of irreversible structural commitments that progressively reshape the accessible configuration space of the universe.Building on recent non-Markovian extensions of cosmology in which memory kernels link the present expansion to a weighted history of nonlinear structure, the paper elevates these results into a broader physical principle. Across simulations, observations, and phenomenological reconstructions, structure formation consistently generates retarded responses that act as an effective drag on cosmic expansion. The paper argues that such memory effects are not merely technical features of coarse-grained dynamics but are surface manifestations of a deeper constraint-forming process.This synthesis paper introduces the concept of \textit{structural commitment} as an irreversible transition that permanently restricts future dynamical possibilities. Within this framework, temporal direction emerges naturally from the accumulation of constraints rather than from entropy growth alone. Entropy describes evolution within an accessible state space; structural commitment governs how that space itself contracts over cosmic history.A minimal formal description is presented in which cosmological evolution proceeds on a progressively constrained manifold. The study shows how multiscale memory kernels provide empirical evidence for this process, forming a hierarchy that runs from fast, viscosity-like relaxation on nonlinear scales to slow horizon-level responses. Several observational and theoretical predictions follow, including increasing history sensitivity at late times and the generic emergence of long effective memory horizons from kernel mixtures.Rather than introducing new microphysics, this work synthesizes existing non-Markovian results into a unifying interpretation: the arrow of time is the macroscopic record of constraints the universe can no longer reverse.