Entropy Density at the Density Limit: A Radiation and Spin-Fluid Estimate

At the limit, the thermal energy exceeds the Fermi energy of the neutron fluid, so the spin carriers are not a cold degenerate gas at the turnaround; they are thermally disordered. The entropy density is enormous by laboratory standards yet finite, and its finiteness traces directly to the finiteness of the temperature ceiling. The computation is performed from stated assumptions in a density-limited bounce, in which the neutron-branch limit density sets a maximum density, a finite bounce temperature, and a minimum horizon size. Headline values from the deposited calculation are: T_bounce_K = 3.28e+22; s_rad_J_K_m3 = 3.55e+52; s_rad_per_kB_m3 = 2.57e+75; n_neutron_per_m3 = 5.80e+84; E_F_J = 1.03e+16; E_F_eV = 6.40e+34; kBT_over_EF = 4.41e-17. The study is simulated and computed, not measured, and its conclusions are stated at the precision the stated assumptions support.