What exactly are the theoretical motivations for considering space and time as a four dimensional continuum? Is it a natural consequence of requiring that the speed of light is independent of the frame of reference that it is measured in, since this implies that time and time are not absolute, but depend on the frame of reference that one measures them in, i.e. they are relative quantities. Also, requiring the constancy of the speed of light and that the laws of physics are independent any particular inertial frame, requires that spatial and temporal coordinates transform via the Lorentz transformations from one inertial reference frame to another. Such transformations explicitly "mix-up" spatial and temporal coordinates, such that the temporal coordinate of the "new" inertial frame is dependent on the spatial and temporal coordinates of the "old" inertial frame (that one has transformed from), and likewise for the spatial coordinates. Finally, unlike in classical mechanics where the spatial line element is frame independent, it is a combination of temporal a spatial coordinates that form a frame independent quantity, suggesting that the "natural" geometry is four dimensional, forming a continuum called "spacetime", with a length in this four dimensional spacetime being determined by this new combination of spatial and temporal coordinates. Is this in any way a correct motivation for considering spacetime instead of space and time as separate entities?