On Wave-Particle Duality
  By means of a thought-experiment, consisting of an interference experiment with two interfering beams, it is shown that it can be demonstrated experimentally that with one single particle a wave can be associated which propagates in space and time as a physical reality, i.e. that it should not merely be considered as a distribution of probabilities. The notion "physical reality" should be understood such that, when this physical reality is considered in a particular space at a particular time, it should be experimentally possible to influence this reality in such a way that future results of experiments show unambiguously that this reality has been causally influenced by the experimental act in this space and at that time. 
W. De Baere