Take movement for example. Forces acting up, down, or from side to side. You make theories to explain it all, but you might well remember that it was you that invented them all. For Mach there was no reason to believe the rest of the cosmos was doing what your little bit was doing, so science should only describe not try to explain. Even description is relative. Am I moving or is the back ground? Or take the position of a star. It depends on the position you see it from, which depends on the date and time, which in turn depends on the position of the earth, in a solar orbit, in a solar system, moving around the edge of a Galaxy which may be moving away from other Galaxies. Say that you've decided that I'm moving and the background is standing still. Is the background moving relative to something else?
James Burke (science historian)