  The proposal that the one-parameter solutions of the real part of the
Schrodinger equation (quantum Hamilton-Jacobi equation) can be regarded as
`quantum particle trajectories' has received considerable attention recently.
Opinions as to their significance differ. Some argue that they do play a
fundamental role as actual particle trajectories, others regard them as mere
metaphysical appendages without any physical significance. Recent work has
claimed that in some cases the Bohm approach gives results that disagree with
those obtained from standard quantum mechanics and, in consequence, with
experiment. Furthermore it is claimed that these trajectories have such
unacceptable properties that they can only be considered as `surreal'. We
re-examine these questions and show that the specific objections raised by
Englert, Scully, Sussmann and Walther cannot be sustained. We also argue that
contrary to their negative view, these trajectories can provide a deeper
insight into quantum processes.
