Photon Number as a Fundamental Quantity in Cosmology: A Conceptual Reinterpretation of Temperature, Energy, Mass, and Interactions

This work presents a conceptual reinterpretation of cosmology in which the photon number is treated as the most fundamental conserved quantity in the universe. Rather than placing energy or spacetime at the foundation, this paper argues that temperature, energy, mass, and fundamental interactions emerge as secondary, derived properties from the conservation of photon number and changes in photon states driven by cosmic expansion. Starting from the observational fact that the total number of photons—particularly those of the cosmic microwave background—is conserved after the early universe, the paper reexamines the physical meaning of photon redshift and cosmic cooling. The decrease in energy per photon is interpreted not as a loss without destination, but as a transformation of physical degrees of freedom, leading to the emergence of mass and interaction structures. No new mathematical formalism or particles are introduced. Instead, this work reorganizes the causal and conceptual hierarchy implicit in existing cosmological and physical theories, offering a unified and internally consistent perspective on temperature, energy, mass, gravity, and fundamental interactions. The paper is intended as a foundational and exploratory contribution to conceptual cosmology and the philosophy of fundamental physics.