  We consider the possibility that all particles in the world are fundamentally
identical, i.e., belong to the same species. Different masses, charges, spins,
flavors, or colors then merely correspond to different quantum states of the
same particle, just as spin-up and spin-down do. The implications of this
viewpoint can be best appreciated within Bohmian mechanics, a precise
formulation of quantum mechanics with particle trajectories. The implementation
of this viewpoint in such a theory leads to trajectories different from those
of the usual formulation, and thus to a version of Bohmian mechanics that is
inequivalent to, though arguably empirically indistinguishable from, the usual
one. The mathematical core of this viewpoint is however rather independent of
the detailed dynamical scheme Bohmian mechanics provides, and it amounts to the
assertion that the configuration space for N particles, even N
``distinguishable particles,'' is the set of all N-point subsets of physical
3-space.
