Discrete Relativity — General Relativity: Active Spacetime

The general theory of relativity describes spacetime as a geometric object that curves in the presence of mass and energy, and its expansion as a stretching of that geometry. This paper raises a conceptual question about the physical picture underlying that mathematics — if spacetime curves and stretches, distances between points change, yet the speed of light c is held constant — and proposes a candidate physical picture that resolves the tension: spacetime expansion is a matter of site activation rather than metric stretching. New units of spacetime become active between existing points; the distance between any two adjacent points remains constant, and c remains constant because the unit it traverses never changes. This paper also develops, at the general-relativistic and cosmological scale, a set of consequences that follow if matter and antimatter carry opposite gravitational parity (the central proposal of the Intro paper) — candidate accounts of the matter-antimatter asymmetry, dark energy, the structure of the cosmic web, phenomena currently attributed to dark matter, and a proposed nested hierarchy of force-mediated structure across scales, echoing atomic structure at the cosmic scale. This paper makes no new mathematical predictions distinguishable from GR at currently measurable scales for the active-spacetime question specifically; the gravitational-parity cosmology carries its own testable predictions, detailed in the Intro paper.