Universal_Ground_Oscillation

We present the ψ₀-theory (“Universal Ground Oscillation”) — a quantized Klein-Gordon scalar field in FLRW cosmology with the single postulate that its Compton wavelength equals the Hubble radius (λ_C = R_H). From this assumption follow a natural solution to the Λ-problem via the Cohen-Kaplan-Nelson bound, dark energy as a thawing quintessence, and dark matter as multi-mode excitations of the same background wave. The theory makes concrete, falsifiable predictions testable with DESI DR3, Euclid, and LiteBIRD.