In relativity, the speed of light is the only constant speed; therefore, in which reference frame are you going at e.g. 10c?
Perhaps the CMB is the preferred frame of reference for all motion and this problem has a trivial solution (I am not a physicist), but everyone I’ve seen explain relativity starts with “there is no preferred frame”, and the rest follows.
Perhaps the CMB is the preferred frame of reference for all motion and this problem has a trivial solution (I am not a physicist), but everyone I’ve seen explain relativity starts with “there is no preferred frame”, and the rest follows.