On the Relation between the Psychological and Thermodynamic Arrows of Time

Abstract: In this paper we lay out an argument that generically the psychological arrow of time should align with the thermodynamic arrow of time where that arrow is well-defined. This argument applies to any physical system that can act as a memory, in the sense of preserving a record of the state of some other system. This result follows from two principles: the robustness of the thermodynamic arrow of time to small perturbations in the state, and the principle that a memory should not have to be fine-tuned to match the state of the system being recorded. This argument applies even if the memory system itself is completely reversible and non-dissipative. We make the argument with a paradigmatic system, then formulate it more broadly for any system that can be considered a memory. We illustrate these principles for a few other example systems, and compare our criteria to earlier treatments of this problem.