Blackbody Spectrum

The cosmic microwave background exhibits a near-perfect blackbody spectrum with temperature T = 2.72548 ± 0.00057 K, as measured by the COBE/FIRAS instrument. This precise blackbody form is one of the most stringent tests of standard cosmology, confirming that the early universe reached thermal equilibrium and that photons and matter were tightly coupled for an extended period. The residuals between the observed CMB spectrum and a perfect blackbody are constrained to be less than one part in 10,000 across a wide frequency range, placing extremely tight limits on any energy injection into the photon-baryon plasma between redshifts of roughly 10⁶ and 10³. This precise thermalization requires the universe to have been opaque and strongly coupled for a sufficient duration — a constraint that any alternative to the Big Bang hot plasma must satisfy.

Successive Collision Theory fully satisfies the blackbody spectrum constraint through the simultaneous thermalization mechanism of the superluminal collision. When the two spacetime pockets collided with relative velocity exceeding c, the collision front swept the entire overlap volume faster than any internal signal could propagate, depositing the full kinetic energy instantaneously into the thermalized photon-baryon plasma. This instantaneous, complete thermalization produced a blackbody spectrum with no preferred frequency — the collision deposited energy into the plasma uniformly across photon modes, establishing thermal equilibrium from the earliest post-collision epoch. The pre-existing matter from the two pockets was thermalized into this plasma, contributing baryons and leptons without introducing spectral distortions because the thermalization occurred at temperatures high enough (T > 10⁷ K) for all injected energy to rapidly equilibrate through Compton scattering and bremsstrahlung before the photon distribution could develop spectral features.

The absence of spectral distortions in SCT is guaranteed by the same physics that makes the CMB uniform: the simultaneous, instantaneous energy deposition by the collision front. Any spectral distortion requires either a non-thermal energy injection after thermalization decouples (creating y-distortions) or a chemical potential distortion from energy injection between z ~ 10⁶ and z ~ 5 × 10⁴ (creating μ-distortions). In SCT, the collision itself deposits all energy before any such epoch, so no post-thermalization energy injection occurs at the level that would produce detectable distortions. SCT therefore predicts that PIXIE and future spectral distortion experiments will find y and μ parameters consistent with the standard heating from reionization and structure formation, with no exotic excess — a clean confirmation of the SCT thermalization picture and a distinction from inflation models that can generate detectable primordial spectral distortions.