  In an recent work with the title "Asking Photons Where They Have Been", Danan
et al. experimentally demonstrate an intriguing behavior of photons in an
interferometer [Phys. Rev. Lett. 111, 240402 (2013)]. In their words: "The
photons tell us that they have been in the parts of the interferometer through
which they could not pass." They interpret the results using the two-state
vector formalism of quantum theory and say that, although an explanation of the
experimental results in terms of classical electromagnetic waves in the
interferometer is possible (and they provide a partial description), it is not
so intuitive. Here we present a more detailed classical description of their
experimental results, showing that it is actually intuitive. The same
description is valid for the quantum wave function of the photons propagating
in the interferometer. In particular, we show that it is essential that the
wave propagates through all parts of the interferometer to describe the
experimental results. We hope that our work helps to give a deeper
understanding of these interesting experimental results.
