The anomaly between the amounts of matter and anti-matter have never been satisfactorily explained. What if there are two distinct states present throughout the universe? In one state matter exists and anti-matter is pushed apart by gravitation. In the other state anti-matter exists and matter is pushed apart by an equivalent force. Thus we see our universe expanding but can not see the anti-matter. In the anti-matter state that universe is expanding but the matter universe is invisible. In the anti-matter universe gravitation would be equivalent to dark matter.
If such a thing could exist the anti-photon could be undetectable in an environment composed of matter.