Clifford Geometry as a Natural Minimal Framework for Causality, Unitary Time Evolution, and Non-Degenerate Volume

Preprint. Publicly released on Zenodo prior to journal submission. This paper formulates an operational carrier-selection problem for relativistic physics: determine the minimal unital associative algebra that simultaneously encodes Lorentzian geometry, realizes the Spin(3,1) sector with standard spinor representations, and supports the phase structure required for unitary time evolution—without modifying dynamics on the base metric.Under an explicit requirement set (R1–R5), the main result is a categorical uniqueness statement: the real Clifford algebra Cl(3,1) is selected as the unique minimal solution via its universal (initial) property, and admissible constructions factor uniquely through it. The manuscript also clarifies how an intrinsic complex structure arises from the pseudoscalar (I² = −1), distinguishing intrinsic phases from externally adjoined complexification. Version 2 notes. Major rewrite: restructured into a JMP-style format with explicit requirements (R1–R5) and a universal-property uniqueness theorem; expanded the intrinsic complex-structure discussion; removed self-referential related-preprint metadata.