This work introduces the Photon-Sea framework as a foundational physicalsubstrate underlying all observable phenomena. The universe is modeled as acontinuous photon sea possessing a zero-frequency, infinite-wavelength groundstate. Within this framework, mass, gravity, quantum nonlocality, dark matter,and cosmic acceleration emerge as inverse-frequency excitations of the photonsea rather than as intrinsic properties or fundamental entities. A central result of the theory is an inverse mass–frequency relation linkingatomic mass, excitation frequency, and atomic number through a universalconstant empirically extracted from atomic data. The framework provides aconceptual and mathematical basis for observer-induced physical properties,emergent gravity without singularities, and late-time cosmic accelerationwithout a fundamental cosmological constant. This paper is a conceptual and phenomenological extension of the MyominAungUnified Theory (MUT v3.0), providing a field-theoretic and physicalinterpretation of the mass–frequency principles introduced therein. It isintended to serve as a supplementary and exploratory foundation for subsequentdynamical, Lagrangian, and observational studies.