As per special theory of relativity, no inertial reference frame is special! If a space ship is moving at 100 m/s, no one can conduct an experiment to determine whether it is moving at 100 m/s or the rest of the universe is moving to the opposite direction at -100 m/s, if I understand the descriptions correctly! But what what about the huge difference in kinetic energy between these two scenarios? If the rest of the universe is moving in the opposite direction, won't it require huge energy? If an experiment can be devised to detect this difference in the energy of the whole system, can't it say if the space ship is moving or the rest of the universe is moving?