Photon and "anti-photon" annihilation? In quantum field theory pairs of virtual particles can appear from vacuum and quickly annihilate each other, for example an electron/positron or a proton/antiproton. But how does this work with photons?From what I know, the photon is its own anti-particle. So the "anti-photon" is just another photon. But how can a real photon annihilate an other "real" photon? Real photons are everywhere, so in that case photons would annihilate eachother all the time?