A model is presented that unifies the core principles of the Charge Conjugation, Parity, and Time-Reversal (CPT) theorem within a single conceptual framework. Additionally, the model integrates the time-symmetric structure of CPT invariance with the asymmetric thermodynamic arrow of time. It emphasizes that the time component of CPT encodes formal symmetry operations and not causal mechanisms at macroscopic scales. Concepts from the model are extended to the retarded (forward-in-time) and advanced (backward-in-time) wave solutions of Maxwell’s equations for electromagnetism. They show that the temporal symmetry between these waves reflects the time-symmetric structure of CPT invariance. And as such, it is likely that the wave solutions do not directly encode macroscopic causal activity. This aligns with Maxwell’s equations, which are not inherently causal, but which are typically interpreted in causal terms in established practice. This also has direct implications regarding the ontological status of advanced waves. The CPT model is further extended to the settings of quantum mechanics and general relativity, where it appears to offer a small advance toward their integration.