Empty wave detecting experiments: A comment on auxiliary "hidden" assumptions

Empty-wave theories have been with us for almost a century as part of the effort to find a causal interpretation of quantum mechanics. Several experiments were proposed with the aim of detecting these waves or their effect. It may be that the most known experiment concerning this issue is that of Wang, Zou, and Mandel. The experiment achieved negative results. In the following we wish to emphasize that the latter experiment has not confronted the full range of possible empty-wave models. In fact, to our mind, it made use of an auxiliary assumption that is far from warranted. If such an assumption is not made, this experiment, and all other experiments of its kind, are not able to detect the effects of the conjectured empty waves. We wish to put an emphasis on this assumption as a pointer indicating the direction in which new models should be searched for.