  Within the class of ontological interpretations of quantum theory where a
physical system comprises a particle and a field (wavefunction) guiding it, an
empty wave is a segment of the wavefunction not containing the particle. We
examine the impact of this concept on the debate between the epistemological
and ontological viewpoints. The theoretical merits of the empty wave in
avoiding the wavefunction collapse hypothesis, and in supplying conceptual
precision in the application of quantum mechanics, are emphasized. Particular
reference is made to path detection in interferometry and it is shown how a
consistent application of the particle and empty wave concepts dispels the
suggestion that this is a <surrealist> theory. The problem of how the reality
of an empty wave might be demonstrated by its effect on other systems is
examined and general arguments advanced against this possibility. However,
these arguments are not conclusive and we describe how the technique of
protective measurement suggests a method to probe the empirical implications of
empty waves and potentially distinguish between the epistemological and
ontological perspectives.
