sentences:  Alfons Stahlhofen and Günter Nimtz developed a mathematical approach and interpretation of the nature of evanescent modes as virtual particles, which confirms the theory of the Hartmann effect.However, an analysis by Herbert Winful suggests that the Hartman effect cannot actually be used to violate relativity by transmitting signals faster than "c", because the tunnelling time "should not be linked to a velocity since evanescent waves do not propagate".Winful means by this that the photons crossing the barrier are virtual photons, only existing in the interactions and could not be propagated into the outside world.