Consider a gedanken(=thought) experiment where I am tracking the motion of the electron in a hydrogen atom with a time resolution of (say) $\Delta t = 10^{-20}$ seconds. Further assume (for simplicity) that the proton is stationary. In quantum field theory we talk about forces carried by virtual particles. Therefore, the Coulomb interaction between the proton and electron in this hydrogen atom is a result of the exchange of virtual photons. However, we do not need to pull out our QED machinery because the electron on average is not energetic (or fast) enough. Also, the number of virtual photons exchange between a *single* pair of proton-electron that the quantum-ness of EM field is washed out and we can treat it classically. In other words, in this limit we do not need to think in terms of virtual photons.

Now, in this thought experiment the proton vanishes at $t = 0$. The absence of the proton will not be felt by the electron until $t = a\_0/c \,(\approx 17\Delta t$); $a\_0$ and $c$ are the Bohr radius and speed of light. Assuming causality I would expect the electron to fly off (because it is no longer bound) at this point in time ($17\Delta t$). But virtual photons can exceed $c$. Then won't the electron know that proton is disappeared before $17\Delta t$?