2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/214296We show that the semiclassical approximation to the Wheeler-DeWitt equation for the minisuperspace of a minimally coupled scalar field in the spatially flat de Sitter Universe prompts the existence of an initial power-law evolution driven by non-adiabatic terms from the gravitational wavefunction which act like radiation. This simple model hence describes the onset of inflation from a previous radiation-like expansion during which the cosmological constant is already present but subleading.LaTeX, 8 pages, no figures; final version to be published in JCAPGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext