Description: The double-slit experiment—often called "the only mystery" of quantum mechanics—finds a straightforward resolution in the Lattice Field Medium (LFM) framework. When individual particles pass through two slits and produce an interference pattern, standard quantum mechanics invokes wave function collapse and the measurement problem. In LFM, there is no mystery: the "particle" IS a wave packet in the substrate, and waves naturally diffract and interfere. Using full GOV-01 + GOV-02 coupled dynamics, we demonstrate: A single E pulse propagates toward a χ barrier with two slits The pulse diffracts through both slits simultaneously Interference fringes appear on the detection screen Blocking one slit destroys the interference pattern The same equations that produce gravity (χ wells), dark matter (χ memory), atoms (bound E states), and molecules (overlapping χ wells) also produce wave-particle duality—which is simply wave dynamics. No collapse, no observer effect, no mystery.