The remaining 95% must be something dark: dark matter and dark energy. More granular simulations and observations can reveal dark matter substructure as well, with the data strongly agreeing with cold dark matter’s predictions. It remains an unproven assumption that dark matter is quantized and discrete: i.e., that dark matter behaves as a particle. (This applies even if dark matter is its own antiparticle, which is a feature of many dark matter scenarios.) The constraints on strongly interacting dark matter, as well as the constraints on electromagnetically interacting dark matter (either charged, magnetically, or with photons) are profound and incredibly stringent.