  We present a theoretical model which allows to keep track of all photons in
an interferometer. The model is implemented in a numerical scheme, and we
simulate photon interference measurements on one, two, four, and eight slits.
Measurements are simulated for the high intensity regime, where we show that
our simulations describe all experimental results so far. With a slightly
modified concept we can also model interference experiments in the low
intensity regime, these experiments have recently been performed with single
molecules. Finally, we predict the result of polarization measurements, which
allow to check the model experimentally.
