Against dogma: On superluminal propagation in classical electromagnetism

It is deeply entrenched dogma that relativity theory prohibits superluminal propagation. It is also experimentally well-established that under some circumstances, classical electromagnetic fields propagate through a dielectric medium with superluminal group velocities and superluminal phase velocities. But it is usually claimed that these superluminal velocities do not violate the relativistic prohibition. Here I analyze electromagnetic fields in a dielectric medium within a framework for understanding superluminal propagation recently developed by Geroch, 1996 and Geroch, 2011 and elaborated by Earman (2014). I will argue that for some parameter values, electromagnetic fields do propagate superluminally in the Geroch–Earman sense.