A Bound–Free Decomposition of the Stress-Energy Tensor

The dynamical laws of fundamental physics are largely time-reversal symmetric, yet macroscopic processes exhibit pronounced irreversibility. The standard resolution combines statistical mechanics with a low-entropy initial condition for the universe — an account that has well-recognized structural limitations: it does not identify a dynamical mechanism producing irreversibility, and it grounds the arrow of time in an unexplained boundary condition. This paper proposes that an additional coupling between bound energy (energy contributing to a localized rest mass) and free energy (energy in propagating modes) may provide a candidate dynamical contribution to the macroscopic asymmetry described by the Second Law. The proposal does not modify microscopic time-reversibility, does not eliminate the Past Hypothesis, and is not a replacement for statistical mechanics. A preliminary covariant formulation is developed: the stress-energy tensor is decomposed into bound and free components, a candidate source tensor S^μν is proposed in toy form, and the resulting modification to the Einstein field equations is examined. The constraints on the coupling from existing equivalence-principle tests are noted, and the work required to convert the proposal into a quantitative theory is explicitly identified, including verification of conservation conditions, derivation of S^μν from a Lagrangian principle, and computation of cosmological signatures distinguishable from ΛCDM.