Whilst not having charge themselves, photons and Z bosons, none the less do interact with particles carrying the relevant quantum charge: electrical charge ( Q ϵ ) for photons (γ), and left and right weak charges (Q L, Q R) for Z bosons (Z). They cannot interact with other γ or Z directly, and except at extremely high energies, usually do not interact with other γ or Z at all. However, because of quantum uncertainty even low energy versions of either particle can briefly split into a particle-antiparticle pairs each of which happens to have the electrical charge needed to interact with a γ, or the left or right weak charge needed to interact with Z, or both. After that interaction has happened, the particle-antiparticle pair recombines into the same γ or Z particle that originally split, precluding the intermediate pair – whatever it may have been – from ever being observed: The only observed effect is the change in the recombined particle's momentum. This disappearing-act makes it appear that a Z - Z or Z - γ or γ - γ interaction occurred.