okay, things to do with relativity probably. how do you explain these: 1) 2 electrons are moving with respect to an observer, with a speed greater than the speed of light in that medium (not vacuum). so, the electrons, by cerenkov effect should emit photons, as should be observed by the observer. but, since the charges are at rest with respect to each other, an observer moving along with them such that relative velocity is 0, shouldnt observe any photons. now, how is it possible that the photons are being emitted but not being observed? 2) in a same conditions, the first observer should observe the charges moving under influence of both electric and magnetic fields whereas the second observer should observe them to move under only electric field. so, the trajectories calculated by them will be different and each of them is correct in his frame of reference. but how can the same charges move in two different ways?
The high speed electrons are bumping into molecules of the medium (e.g. H2O molecules). The molecule's electron is bumped into a higher orbital and then drops down again releasing a photon. The photon can be seen observed no matter how fast some observer is moving, even if the observer is moving at the same velocity as the electrons. The electron(s) moves relative to an observer. If there are two observers, then the electron moves with respect to each observer.
there is "covraiance" such that similar effects on electrons will be observed from any "inertial frame". this does not violate the "symmetry".