Thermodynamics of the SGCC Bounce: Bekenstein–Hawking Entropy Conservation, the Horizon Budget, and the Refutation of Heat Death

We present a complete thermodynamic analysis of the Self-Generated Cyclic Cosmology (SGCC) bounce within the Riemann–Cartan framework. Using the Bekenstein–Hawking entropy of the supermassive black hole (SMBH) population as the primary thermodynamic observable, we demonstrate that the classical heat death of the universe is not a physical fate within the SGCC framework, but a limit that is never reached because the torsional bounce interrupts the cosmic timeline 81 orders of magnitude before Hawking evaporation completes. We compute six independent thermodynamic quantities. (i) The Hawking evaporation timescale τH ∼ 3.6×1091 yr for a median SMBH mass of 1.2×108 M⊙, compared to a typical bounce time tbounce ∼ 7 Gyr, giving τH/tbounce ∼ 2.6 × 1081. (ii) Area conservation through the Kruskal throat: ∆SBH/SBH < 10−13, confirming the horizon area as a topological in variant across the bounce. (iii) The horizon budget: the entropy density s = SBH/Vhorizon is 102–103 times higher at the bounce than today, demonstrating that the universe is far from thermodynamic equilibrium at the bounce. (iv) Pre-bounce accretion: ∆M/M < 10−15 — mass and entropy are conserved to numerical precision. (v) The adiabatic cycle invariant J = SBH/Srad = 3.617 × 10−16, constant across the bounce, establishes thermodynamic self-consistency of the SGCC cycle. (vi) The von Neumann entropy of the torsion field SvN ∼ 1042 J K−1 quantifies the information encoded in the spin-memory mechanism of Paper B. All results are consistent with the second law of thermodynamics: entropy is non decreasing within each cycle, but the cycle resets before the maximum entropy state is reached. The SGCC does not violate thermodynamics; it provides a finite cycle length that preempts heat death. Four appendices extend the analysis: the covariant entropy bound of Bousso (1999) is satisfied by 12 orders of magnitude for all εpv (Appendix C); and a first-principles calibration of the torsion amplitude from the LoTSS DR2 SMBH spin density yields |T0|SMBH ≃ 8.58 × 10−41H0 2 — 36 orders below the Solar System bound — providing a theoretical justification for the null CMB result of Paper B (Appendix D).