[AntonioLao]

in a many worlds scenario, who is the timekeeper? If there is one then this keeper must have a clock for each world and more than likely the rates of these clocks might not be the same and their zeros might not start at the same spacetime location (these must be possible in order not to violate the principle of special relativity). The singular solution that the rates are the same and the zeros are the same is for all the worlds to be at rest relative to each other, that is to say they are all in one inertial frame with relative velocities equal zero.