Relativity says all inertial frames of reference are equally valid and true. From a photon's point of view the entire cosmos is flattened into a two-dimensional timeless plane.

Moving reference frames – aircraft problem Aircraft A and B are flying on the same horizontal plane, each with a constant speed. Aircraft A is traveling on a straight path, whereas the path of B is ...

Newton never explicitly described inertial reference frames, but they are a natural consequence of his First Law of Motion.