When the Relic Neutrinos Decoupled: Temperature, Redshift, Cosmic Age, and Horizon Content at Last Scattering of the Weak Interaction

Neutrinos decoupled when the universe was about one second old. At a representative decoupling temperature of 2 MeV the corresponding redshift is 1.189e+10 and the radiation-era age is 0.184 seconds; at 1 MeV the redshift is 5.946e+09 and the age 0.738 seconds. This paper computes the decoupling epoch consistently across the flavour-dependent temperature range, converts among temperature, redshift, and age with stated conventions, and estimates how many relic neutrinos lay inside one horizon volume at decoupling. The epoch is remote from any torsion-bounce density by an enormous factor, so the frame changes none of these numbers, which the paper records as a plain negative result. The study is computed from stated assumptions, not measured.