  The concept of wave-particle duality, which is a key element of quantum
theory, has been remarkably found to manifest itself in several experimental
realizations as in the famous double-slit experiment. In this specific case, a
single particle seems to travel through two separated slits simultaneously.
Nevertheless, it is never possible to measure it in both slits, which naturally
appears as a manifestation of the collapse postulate. In this respect, one
could as well ask if it is possible to "perceive" the presence of the particle
at the two slits simultaneously, once its collapse could be avoided. In this
article, we use the recently proposed entanglement mediation protocol to
provide a positive answer to this question. It is shown that a photon which
behaves like a wave, i.e., which seems to be present in two distant locations
at the same time, can modify two existing physical realities in these
locations. Calculations of the "weak trace" left by such photon also enforce
the validity of the present argumentation.
