Paper XXIX: CMB Acoustic Peaks as Gravitational Echoes and the Hubble Tension as T1 Recovery

The CMB acoustic peaks are proposed to arise from gravitational echoes: the Big Bang collision of Papers I and XXIII produced gravitational waves that bounced between the brane and the 5D bulk boundary, creating a ringing pattern imprinted on the photon-baryon plasma. The odd/even peak ratio, currently attributed to dark matter, is explained by the brane-bulk echo amplitude ratio. The Hubble tension (6σ as of 2025) is resolved as a T1 recovery transient: the sump relaxation time Tₛump = 72. 65 Gyr globally gives H0 = 67. 4 km/s/Mpc (CMB) ; Tₛump = 60. 84 Gyr locally gives H0 = 73. 0 km/s/Mpc (SH0ES). The local baryonic overdensity shortens the local T1 relaxation time by ∆Tₛump = 11. 81 Gyr. The S8 tension is resolved by T2 dephasing suppressing small-scale power. Two new CMB predictions follow: a step feature in the Silk damping tail at l ∼2000 from the QCD epoch (Prediction 56), and large-scale CMB anomalies (axis of evil, hemispherical asymmetry) from the G2 symmetry axis (Predictions 62-63). Part of the One-Octonion Brane-Bulk Framework series. Anchor DOI: 10. 5281/zenodo. 19120873. Community: one-octonion-brane-bulk. Author: Bharathi Dasan Jagadeesan, M. D. , University of Minnesota. ORCID: 0000-0002-1143-941X.