The Φ₀ Triad: How One Number from 5D Geometry Explains Hubble Tension and Black Hole Shadows

Version 4.0 - Correction Notice This version supersedes V.1 and V.2 of "The Cosmic Submarine". A factor-of-2 error in the original photon sphere derivation led to the incorrect values "6.066% efficiency" and η = 1.06066. Those values and all related claims are withdrawn. The mathematically consistent result from the full 5D Randall-Sundrum metric is η = √(1 + Φ₀) = 1.03033, a 3.03% diameter enhancement over General Relativity for M87*. The complete, corrected derivational framework is published in: DOI: 10.5281/zenodo.20403335 Do not use or cite V.1 or V.2. This v4.0 contains the correct predictions testable by ngEHT 2027.