In Einstein's general relativity, coordinates like x, y, z, and t are not only "relative" in the global sense of translations like t → → t + C , rotations, etc., but become completely arbitrary, so that, for example, one can define an entirely new time-like coordinate according to some arbitrary rule such as t → → t + t 3 / t 0 2 , where t 0 has dimensions of time, and yet Einstein's equations will have the same form.