  The concept of quantum superposition is reconsidered and discussed from the
viewpoint of Bohmian mechanics, the hydrodynamic formulation of quantum
mechanics, in order to elucidate some physical consequences that go beyond the
simple mathematical idea of linearly combining vectors in a Hilbert space.
Specifically, the discussion turns around the connection between symmetries
characterizing the wave function and the behavior in time displayed by the
quantum flux when the latter is analyzed in terms of streamlines (Bohmian
trajectories). This is illustrated with a series of analytical results and
numerical simulations, which include Young's two-slit experiment,
counter-propagating wave packets, grating diffraction and quantum carpets
(e.g., Talbot carpets), and diffraction under confinement conditions. From the
analysis presented it follows that quantum paradoxes appear whenever symmetries
related to interference are neglected in the interpretation and understanding
of the corresponding phenomena.
