 The uncertainty principle implies that individual photons may travel for short distances at speeds somewhat faster (or slower) than "c", even in vacuum; this possibility must be taken into account when enumerating Feynman diagrams for a particle interaction.However, it was shown in 2011 that a single photon may not travel faster than "c".In quantum mechanics, virtual particles may travel faster than light, and this phenomenon is related to the fact that static field effects (which are mediated by virtual particles in quantum terms) may travel faster than light (see section on static fields above).