Abstract

Within a projection-based framework, effective physical descriptions are understood as aris- ing from the preservation of specific invariance structures under projection from a more general representational level. In this setting, projection provides the organizing principle, invariance stabilizes physical structure and compatibility determines when distinct descriptions may coexist consistently. This paper examines the implications of this framework for the status of spacetime. Rather than treating spacetime as a fundamental background in which physical processes occur, space- time is interpreted as an effective coordinative structure that becomes available when projection- invariant descriptions remain mutually compatible. Structural–coordinative projections jointly stabilize localization, metric comparability, causal ordering and inter-observer consistency, thereby enabling a shared spacetime description. Other projection classes remain compatible with this structure, restrict its domain of applicability or locally terminate it without generating spacetime themselves. The analysis does not modify existing physical theories or introduce new dynamical prin- ciples. Instead, it clarifies the conditions under which spacetime-based descriptions apply and explains why spacetime exhibits both robust stability in familiar regimes and apparent break- down in others. By framing spacetime in terms of structural coordination rather than as a fundamental background, the paper provides a unified and non-mysterious perspective on en- tanglement, measurement, and spacetime breakdown, while remaining fully consistent with established physical theory and practice.