  Quantum effects that materialize always fulfill the conservation laws and
principles of physics. Physical interactions require the presence of sources
and vehicles of conserved quantities. Generally, on-shell particles are
sources, and off-shell particles are vehicles of conserved quantities. We have
found that when either the source or vehicle is missing, quantum effects cannot
materialize. Our findings resolve the alleged violation of complementarity in
the Afshar experiment. Additionally, our findings indicate that galactic
neutrinos should be treated as a classical ideal gas. To this end, we present a
simplified model of a classical ideal gas of neutrinos that accounts for
effects attributed to dark matter to a reasonable degree of approximation.
