Does faster than light motion contradict Einstein's theory of relativity?
In this talk, we are going to investigate the
possibility/impossibility of faster than light (FTL) motion in
relativity theory within an axiomatic framework.
We will see that, while the impossibility of FTL motion of observers (reference frames) follows from a few basic assumptions of relativistic kinematics, the existence of FTL particles is logically independent of both relativistic kinematics and dynamics (even if we assume a strong version of Einstein's principle of relativity).
So relativity theory does not decide (by itself) whether there can or cannot be FTL particles. However, relativistic dynamics implies that the relativistic masses of FTL particles do not increase but decrease with their speeds.