  The most puzzling issue in the foundations of quantum mechanics is perhaps
that of the status of the wave function of a system in a quantum universe. Is
the wave function objective or subjective? Does it represent the physical state
of the system or merely our information about the system? And if the former,
does it provide a complete description of the system or only a partial
description? We shall address these questions here mainly from a Bohmian
perspective, and shall argue that part of the difficulty in ascertaining the
status of the wave function in quantum mechanics arises from the fact that
there are two different sorts of wave functions involved. The most fundamental
wave function is that of the universe. From it, together with the configuration
of the universe, one can define the wave function of a subsystem. We argue that
the fundamental wave function, the wave function of the universe, has a
law-like character.
