actually there is a pretty sound physics rooted explanation for the operation of "lightsabers"
See it is in fact, plasma contained in a powerful magnetic field that loops back on itsself and is maintained as stated previously by the modulation and focusing crystals in the hilt. this is actually entirely feasible, the only point where it falls apart is the sheer amount of power it would require to maintain. Of course one could postulate that a society that can travel at near light speed probably can miniaturize fusion reactors or something. point is, with a viable power source, it is a not impossible to make plasma behave that way.