  We outline how Bohmian mechanics works: how it deals with various issues in
the foundations of quantum mechanics and how it is related to the usual quantum
formalism. We then turn to some objections to Bohmian mechanics, for example
the fact that in Bohmian mechanics there is no back action of particle
configurations upon wave functions. These lead us to our main concern: a more
careful consideration of the meaning of the wave function in quantum mechanics,
as suggested by a Bohmian perspective. We propose that the reason, on the
universal level, that there is no action of configurations upon wave functions,
as there seems to be between all other elements of physical reality, is that
the wave function of the universe is not an element of physical reality. We
propose that the wave function belongs to an altogether different category of
existence than that of substantive physical entities, and that its existence is
nomological rather than material. We propose, in other words, that the wave
function is a component of physical law rather than of the reality described by
the law.
