 According to Schaffer, the best argument for the possibility of piling—hence the best argument against SI—is rather provided by the existence of so-called bosons (photons being one example). Bosons are entitites which do not obey Pauli’s Exclusion Principle, and hence such that two or more bosons can occupy the same quantum state. A ‘one-high’ boson-pile is hence empirically distinguishable from a ‘two-high’ one, which means that the possibility of piling in general is not ruled out even if we accept an Eleatic principle. Schaffer (2001: 255) suggests we solve this problem for SI by considering the wave—not the particle/boson—as the way the object ‘really’ is.  But this solution comes with complications of its own for the proponent of SI. For, “[t]he wave function lives in configuration space rather than physical space, and the ontology of the wave function, its relation to physical space, and its relation to the relativistic conception of spacetime which SI so naturally fits remain deeply mysterious” (Schaffer 2001: 256).