What does this mean for mass measurements? Basically the reason we can't travel faster then C (afaik) is because of the way relativistic velocities add. ie .8c +.2c +.2c +.2c = .935 c or something ...

Special relativity, even though it's over 100 years old, is still one of the most puzzling and perplexing discoveries about the nature of the Universe itself. The (Newtonian) laws of physics that ...