We study the quantum cosmology of a closed, spatially-homogeneous and isotropic FRW minisuperspace model, with electromagnetic radiation representing the matter content. We solve the associated Wheeler-DeWitt (WDW) equation using the holographic regularization method, and show that the electromagnetic zero-point energy forms the vacuum energy, and provides a unified resolution to the horizon, flatness, singularity, and cosmic coincidence problems. This quantum cosmology approach forms an alternative to the usual inflationary paradigm and can be extended to more general matter contents and emergent gravity schemes.