Space Density Theory: A Unified Scalar Field Framework for Dark Matter, Dark Energy, and the Hubble Tension

SDT proposes that space is a physical medium with a scalar density field governed by a double-well potential. This paper presents the complete classical framework including: rotation curve fits for 172 SPARC galaxies (87% pass rate, 2 global parameters), derivation of the MOND acceleration scale as the SDT phase transition critical point, 43% improvement over the MOND/RAR formula, Hubble tension reduction from 3.7 to 0.5 sigma, and 15 falsifiable predictions. Companion papers cover the cosmological origin (CEU), quantum connections, and FRB dispersion.