I maintain that quantum mechanics is fundamentally about a system of N particles evolving in three-dimensional space, not the wave function evolving in 3N-dimensional space.
Versions of quantum mechanics that postulate the existence of the wave function either cannot account for our experience or are metaphysically extravagant without reason. If they postulate just a 3N-dimensional space in which the wave function evolves, they have trouble accounting for why conscious experiences exist at all. If they postulate the 3N-dimensional space in which the wave function evolves and a three-dimensional space in which particles evolve, then there is no good reason to believe in the 3N-dimensional space; the role the wave function plays in the evolution of particles can better accounted for by postulating extra properties that the particles have.
In quantum mechanics, the wave function of a N-body system is a mathematical function defined in a 3N-dimensional configuration space. We argue that wave function realism implies particle ontology when assuming: (1) the wave function of a N-body system describes N physical entities; (2) each triple of the 3N coordinates of a point in configuration space that relates to one physical entity represents a point in ordinary three-dimensional space. Moreover, the motion of particles is random and discontinuous.
The question concerning the dimensionality of our fundamental physical space is arguably one of the most profound cases of underdetermination in non-relativistic quantum mechanics. Those who take the wave function to represent fundamental reality think that the world fundamentally has 3N dimensions, where N is the total number of particles. Against this, various versions of quantum mechanics postulate certain entities in 3-dimensional space as fundamental. An important argument for the latter view suggests that this is not strictly a case of underdetermination of theory by evidence, because a view that does not include some entities in 3-dimensional space fails to explain how there can be empirical evidence for quantum mechanics in the first place. A critical assessment of this argument will clarify how the debate on dimensionality depends on the evaluation of non-empirical virtues which is well-known from other debates on underdetermination.