This paper presents a naturalistic argument for the macroscopic spatial topology of the universe. The argument presupposes no intervention, no selector, no free parameters, and no anthropic principle. It proceeds from a single constraint—non-intervention—and derives the unique external spatial structure of the universe through a stepwise process of elimination. The starting premise is that the universe is neither designed, chosen, nor maintained. Any feature that requires external intervention to be established—sustaining, demarcating, pressing into symmetry, or selecting among possibilities—cannot exist in a universe devoid of a hand. From this, three initial criteria follow: the universe must be finite (infinity requires continuous impetus), must be a closed manifold without boundary (a boundary requires a boundary-drawer), and must be inherently asymmetric (symmetry requires global pressing). With these criteria, dimensionality is examined. One- and two-dimensional closed manifolds are either symmetric, thus requiring a pressing hand, or asymmetric, yet requiring selection from infinitely many possibilities. Neither can stand without intervention. In four or more dimensions, compact manifolds admit no finite classification; any concrete realization demands selecting a point from an immense moduli space, thereby introducing a selector. Hence, higher dimensions are likewise excluded. Three dimensions alone can simultaneously satisfy finitude, closure, asymmetry, and require no selection. Among closed three-dimensional manifolds, candidates are eliminated one by one: the 3‑sphere S³ is symmetric and requires pressing; the flat torus T³ requires an explanation for its exactly zero curvature and possesses translational symmetry that must be maintained; lens spaces L (p, q) demand two integer parameters; hyperbolic manifolds require a choice from an enormous moduli space; other quotient spaces all contain free parameters or special group selections. The sole remaining blueprint is three-dimensional real projective space RP³ — the quotient of S³ by antipodal identification Z₂. The quotient group is unique (the only group of order two), the action is unique (the antipodal map), there are no free parameters, asymmetry is topologically inherent in the quotient operation, and both closure and curvature are naturally inherited. Conclusion: In a universe without intervention, RP³ is not a chosen solution. It is the only structure that remains after all possibilities requiring a hand have been eliminated. It requires no anthropic principle to explain its existence, for it is simply the form that space necessarily takes when no hand is present. This argument provides a naturalistic foundation for cosmic topology, independent of observation and free of adjustable parameters. Keywords: Non‑intervention principle; naturalistic elimination; cosmic topology; three‑dimensional real projective space; RP³ So, in summary, once we set aside human aesthetics, human choices, and human artificial overcomplication, and imagine ourselves standing on the side of nature itself—what conclusion would we reach? I have offered one possible answer. physical theory;https: //doi. org/10. 5281/zenodo. 19571808 Xinyu Zheng wxsq1638@outlook. com
Xinyu Zheng (Wed,) studied this question.