Consider a photon undergoing pair production and turn into a particle-antiparticle pair. Now play this in reverse, you got a particle and an antiparticle colliding to create a single photon. But in annihilation, the result is two or more photons. Violation of T symmetry? There also seems to be evidence of CP symmetry violation: '[There have been] 32 sightings of muon neutrinos morphing into the electron flavour, compared with just 4 muon antineutrinos becoming the anti-electron variety.' Source: (https://www.newscientist.com/articl...at-why-antimatter-didnt-blow-up-the-universe/) Although the above observations have only reached 2 sigma, many believe that this could be the reason why there is more matter than antimatter in the universe. In order for there to be more matter than antimatter in the universe, there has to be a process that violates CP symmetry, so why is this surprising?