If I want to consider the velocity of distant receding galaxies which may be receding at velocities close to the speed of light can I use SR? I know you are not suppose to use SR with when velocities are close to the speed of light. If a velocity is due to universal expansion does that make a difference? It would seem not, but I am not sure if a velocity due to universal expansion is really a velocity, just like relitivistic mass is not really mass. It is a poor example, I know, but it helps with the point.