Dark Matter: From Particle to Property — A First-Principles Derivation of the Nature of Dark Matter in UD Theory

Dark matter is one of the greatest mysteries in modern physics. The standard theory assumes dark matter consists of one or more unknown particles, but 30 years of direct detection experiments (LUX, XENON, PandaX) have yielded no results. Based on the fundamental axioms of UD theory, this paper demonstrates that dark matter is not a particle, but the condensative tendency of space, U_D. UD theory is based on four fundamental axioms: (1) the universe originates from a critical state U = D; (2) two fundamental attributes exist—U (dispersion, expansion, continuity) and D (condensation, localization, fixation); (3) U and D mutually contain each other; (4) the total quantity is conserved (total normalization axiom). From these axioms, a four-aspect structure emerges: U_U (dark energy), U_D (dark matter), D_D (visible matter), and D_U (quantum fluctuations). Dark matter corresponds to U_D—the D attribute in space. This is a property of space, not a particle. This perspective naturally explains:- Direct detection null: Not a particle, cannot be detected by particle detectors- Gravitational effects: Spatial condensation affects the metric- Cored centers: Field equations yield core solutions, not cusps- Correlation with visible matter: U_D and D_D coupled through field equations- Small-scale cutoff: Exponential cutoff e-r/r_t from the mass term The dark matter density profile is derived from the UD field equations on galactic scales:ρ_DM(r) = ρ_0 (1 + r^2/r_c^2)⁻¹ e-r/r_t Scaling relations on galactic scales:r_c = α R_d, ρ_0 = β Σ_0/R_d, r_t = γ r_c3/2where α, β, γ are dimensionless constants calibrated using galactic rotation curves. On cluster scales, the density profile form remains universal, but the scaling of r_c with mass follows r_c ∝ M0.22, reflecting the significant contribution of hot gas. The transition from M1/3 (galactic) to M0.22 (cluster) is a testable prediction. The distribution is extended to cosmic scales: cosmic web filaments (approximate solution) and cosmic voids (exact solution). UD theory predicts that all future direct detection experiments will continue to yield null results. The necessary hypothesis of dark matter particles is completely eliminated.