Mugnai et al., “Observation of superluminal behaviors in wave propagation”, Phys. Chiao, “Dispersionless, highly superluminal propagation in a medium with a gain doublet”, Phys. Wong, “Linear pulse propagation in an absorbing medium”, Phys. McCumber, “Propagation of a gaussian light pulse through an anomalous dispersion medium”, Phys. Sommerfeld, “Ein Einwand gegen die Relativtheorie der Elektrodynamik und seine Beseitigung”, Phys. Such theories exist already, but so far there is no convincing evidence that could support the withdrawal of relativity in the favor of an alternative theory.Ī. Einstein's theory of relativity, will have to be revised or replaced with newer theories, possibly even allowing for superluminal propagation. Of course, it is conceivable that the currently accepted physical theories, e.g. A so-called precursor is traveling with that speed, but is normally too weak to be detected, except under very special circumstances. For such signals, it can be proven that the earliest time at which that switching event can be observed is limited exactly by propagation with the vacuum velocity. Therefore, a different kind of signal must be considered, where no information at all is sent out before a certain moment of time. For example, a Gaussian-shaped pulse can be detected long before its peak due to the rise of intensity at earlier times. However, the error lies in identifying the peak of the pulse with the temporal position of the carried information. Group velocities larger than then appear to lead to superluminal transmission and can occur e.g. The information then appears to propagate with the group velocity, i.e.
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