This work introduces Temporal Determinacy Geometry, a new theoretical framework in which probability is not an intrinsic property of the universe but a manifestation of underdetermined surface states awaiting temporal completion. A physical state at time ttt is described by mmm observable variables and constrained by nnn independent physical equations. When m=n, the system forms a fully determined reality surface. When m≠n, the system is not probabilistic but simply incomplete, awaiting resolution through the temporal evolution function f(t). In this framework, observable reality is always a two-dimensional closed surface, while the remaining constraints reside in an orthogonal time component expressed symbolically as ictictict. Probability corresponds to the temporary absence of these constraints rather than ontological randomness. Quantum entanglement is reinterpreted as a geometric projection effect on closed surfaces, eliminating the need for nonlocal causation. Temporal Determinacy Geometry integrates closed-surface ontology, determinacy conditions, and orthogonal temporal structure into a unified model of physical reality. This theory provides a deterministic alternative to quantum probability, resolves paradoxes arising from point-particle assumptions, and presents a scale-independent geometric basis for physics.