A Planck-Thermodynamic Foundation for a Linear-Horizon Cosmological Model and Its Implications for Primordial Lithium

Athermodynamic cosmological model recently proposed by Haug exhibits promising features, including a potential resolution of the primordial lithium problem. The model is characterized by a linearly evolving Hubble radius and a horizon-defined cosmic mass. In this work, we show that the temperature-dependent expansion rate assumed in the model follows uniquely from Planck’s law of blackbody radiation combined with the horizon condition. This establishes a first-principles thermodynamic foundation for the model’s initial conditions and clarifies the physical origin of the modified nucleosynthesis dynamics responsible for lithium suppression.