Using drudkh's example cited above and using Einstein's velocity addition formula, closure speed between a particle moving to the right at v and light coming from the right and moving left at c would still be c. Why? Let's use v as the velocity of the particle expressed as a fraction of c and therefore c = 1 closure velocity = (c + v)/(1 + vc/c2) = (1 + v)/1 + v) = 1 If, instead of a particle moving to right at v, we substitute a photon or a light wave moving at c or 1 and still light comes to the left at c or 1, the formula becomes: closure velocity = (1 + 1)/(1 + 1) = 1 Ain't life grand? The max speed attainable is 1 or c. Can we ever have a closure velocity > c? Not according to the above. Someone show me and drudkh wrong!