If we perform the two slit experiment vertically - so the slots are above one another - we should observe a small amount of red / blue shift in the energy of the photons when they hit the screen (due to gravity). The path length from each slit is not symetric so the arriving photons energy would vary depending on the route. This would avoid measuring the photons at the slits but still - over time - assuming the equipment was sensitive enough - predict which path a photon took. Would the arriving energy level of the photon be a combination of the energies of a photon going through both the two slits path? Or always be one of the two energy levels required for it go down either path?