We discuss a set of candidate specifications for dark matter. We show that at least one candidate specification can help explain known ratios of dark-matter effects to ordinary-matter effects and can help explain eras in the rate of expansion of the universe. The ratios pertain to galaxies and galaxy evolution, galaxy clusters, and densities of the universe. The candidate specification reuses, with variations, a set of known elementary particles. We associate the three-word term isomeric dark matter with the dark-matter elementary particles that associate with members of the set of candidate specifications. Regarding galaxy evolution and the rate of expansion of the universe, we deploy multipole-expansion methods that combine Newtonian gravity, aspects of motions of sub-objects of gravitationally interacting objects, and Lorentz invariance.