Virtual photons in macroscopic tunneling

Tunnelling processes are thought to proceed via virtual waves due to observed superluminal (faster than light) signal speeds. Some assume such speeds must violate causality. These assumptions contradict, for instance, superluminally tunnelled music and optical tunnelling couplers applied in fiber communication. Recently tunnelling barriers were conjectured to be cavities, wherein the tunnelled output signal is not causally related with the input. The tests described here resolve that tunnelling waves are virtual, propagations are superluminal, and causality is preserved. Tunnelling and its optical equivalent, the evanescent mode, have been conjectured to involve virtual particles and waves. Evanescent modes are described by imaginary wavenumbers. They are not measurable inside a barrier. In order to make them evident, either the energy of the virtual particle or wave has to be increased up to the barrier’s height or the barrier has to be reduced. Previous experimental tunnelling studies with photons and phonons indicated that the virtual waves or particles are non-local and thus spread instantaneously; the barrier traversal time is zero. However, a superluminal physical signal velocity does not necessarily violate causality; effect does not precede cause. In this study we investigated the propagation of virtual photons by inductive posts in undersized waveguides and in dielectric quarter wavelength lattices.