Ab Initio Derivation of the Hubble Constant From the Single Axiom d = 3

We present an ab initio derivation of the Hubble constant H0 from a single axiom: space has d = 3 dimensions. Using the holographic principle and dimensional analysis, we derive a formula for the number of bits N on the cosmological horizon. Combined with the Bekenstein-Hawking entropy bound, this yields: H0 =pπ/NtPl= 70.3 km/s/Mpc. This value lies exactly between the Planck (67.4) and SH0ES (73.0) measurements,suggesting that the Hubble tension may reflect systematic errors in both directions rather than new physics. We show that only d = 3 produces a universe with a reasonable age (neither instantaneous nor eternal), providing a new anthropic argument for three spatial dimensions. The framework also connects H0 to the primordial entropy S0 = 16π2 ≈ 158 bits, resolving the cosmological constant problem. Keywords: Hubble constant, holographic principle, Dark Geometry, cosmological constant problem, dimensional analysis