It is mentioned in the linked article. Since speed is always relative (to a frame of reference), Special relativity by definition proposes that, nothing can go

It is mentioned in the linked article. Since speed is always relative (to a frame of reference), Special relativity by definition proposes that, nothing can go faster than C. The article gives an example, if a spaceship is traveling at 0.6c, and another spaceship is traveling at 0.6c - away from first first ship. Their relative velocities are not 1.2c, but 0.8c (http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity...)