Superluminal signal velocity is widely assumed to confront Einstein causality and thus the Special Theory of Relativity STR. Actually, there is only the tunneling mechanism known to permit superlum...
Superluminal signal velocity is widely assumed to confront Einstein causality and thus the Special Theory of Relativity (STR). Actually, there is only the tunneling mechanism known to permit superluminal signal velocities at present. The demonstrated negative group velocity experiments don't represent superluminal signal velocities. In those experiments only the signal's peak traveled faster than light and the signal was reshaped. In this Note we shall discuss why tunneling allows superluminal signal velocities. However, opposed to text books on STR we have shown that a superluminal signal beam does not allow the design of a time machine.
Photonic tunnelling experiments have shown that i) the Einstein energy relation is violated, ii) the tunnelling process is non‐local, iii) the signal velocity is faster than light, i.e. superluminal, iv) the tunnelling signal is not observable, since photonic tunnelling is described by virtual photons, and v) according to the experimental results the signal velocity is infinite inside the barriers, implying that tunnelling instantaneously acts at a distance. We think these properties are not compatible with the claims of many text books on Special Relativity, see for instance Refs. [1].
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.