Einstein E=mc2 Threshold: Primordial Radiation Energy-to-Mass Phase Transition in ΛCDM Cosmology

Abstract The ΛCDM model assumes structured initial conditions without providing a mechanism for their origin. Inflation describes the universe's expansion but does not explain how the first gravitationally bound structures formed from a radiation-dominated plasma, nor does it identify the physical trigger that converted that plasma into the matter-dominated universe we observe. We propose that Einstein's 1905 formulation of c – implicit in the rewriting of E=mc² as E/c = mc – may provide the missing trigger: at a critical energy density ρ_crit, we argue the radiation-dominated pre-structure plasma would undergo a first-order phase transition in which the c-threshold forces the resolution of trapped radiation energy into rest mass. This is not, we suggest, a new postulate, but rather Einstein's own insight applied dynamically rather than statically: c may function not merely as a conversion factor between energy and mass, but as the threshold that forces that conversion when the energy density of a region reaches the threshold at which radiation pressure would require superluminal propagation to support the system against its own energy content. This threshold – the moment when a region's Schwarzschild radius equals its physical radius – would trigger a cascade of primordial black hole formation we term the primordial avalanche.