Due to the expansion of the universe, light that originated from a point far enough away will become infinitely red shifted before reaching us. But what does this actually mean?
Let's for illustrative purposes use a wave packet as a model for a propegating photon:
or maybe the tip of a honey spoon:
As the photon moves through space, the expansion will keep stretching it and stretching it until.......? Where does the energy of the photon go?