As if it weren't hard enough already to imagine it in twos, physicists have entangled three photons with each other. Entanglement is a counterintuitive quantum physics phenomenon, in which a particle influences all the others with which it's entangled -- even if the particles are far apart. If one particle is in one state, for example, the others might be in the same state. In this case, however, each photon, which is a particle of light, had the same polarization -- either horizontal or vertical.