Chapter 3: The τ³ Arena: Fiber T² as Microcosm

The fibered product τ³ = τ¹ ×_f T² was constructed in Books I and II. This chapter does not reconstruct it; instead it extracts the physical interpretation. The fiber T² = S¹ × S¹ (torus) is the microcosm: the arena of quantum mechanics, particle physics, and all phenomena at fixed worldline position. The base τ¹ is the macrocosm: the arena of gravity and cosmology (Book V). We describe the geometry of T² as a physical stage, the coordinate structure it carries, and the micro/macro decomposition that organizes Books IV and V.