|Space in Physical Theories|
Space here means the space of the science of mechanics, which encompasses planetary and celestial (i.e., “outer”) space, but is presupposed by the motion—spatial change—of any bodies whatsoever, from the tiniest particles through human-sized bodies to the whole universe. The investigation of space has been perhaps the most fruitful interaction between physics and philosophy.
Physics endows space with specific properties playing a crucial role in determining the motions of bodies, but, despite being omnipresent, space (prerelativistically) is frustratingly inert—not having even the indirect causal effects of subatomic particles, say. Thus physics ascribes substantive properties to space on the basis of indirect evidence, allowing metaphysical bias to influence understanding, and calling (in part) for philosophical clarification.
One of the main strands of this clarification involves the “absolute-relative” debate. In fact a number of (interconnected) debates go under this title, of which two are focused on in the historical development of mechanics: Of all the motions a body has (relative to different frames of reference), which if any are privileged or “absolute”?