Quantum Mechanics as Dimensional Projection: A Geometric Derivation from Compact Extra Dimensions

This paper proves that quantum mechanics emerges as a mathematical necessity when a deterministic classical system possesses compact Kähler dimensions inaccessible to observation. The proof rests on three independent results from established mathematics: Spectral discreteness: The spectral theorem for elliptic operators on compact manifolds guarantees a discrete eigenspectrum, producing superposition and complex phase structure. The uncertainty principle: The Gromov non-squeezing theorem establishes an irreducible lower bound on observable uncertainties, with Planck's constant identified as the symplectic capacity of the compact space. The Born rule: The unique Kähler-compatible L² inner product determines the probability rule P = |ψ|² with no alternatives. Together, these results demonstrate that the complete axiomatic structure of quantum mechanics — complex Hilbert space, superposition, interference, the uncertainty principle, the Born rule, and entanglement — is a necessary consequence of dimensional projection rather than a set of independent postulates. The paper further shows that: The complex numbers in quantum mechanics originate from the complex structure (J) of the compact manifold, providing a geometric explanation for recent experiments ruling out real-valued quantum mechanics (Renou et al., Nature 2021; Chen et al., PRL 2022). Unitary time evolution arises because the complex structure converts what would otherwise be dissipative dynamics into probability-preserving oscillation. The number field of quantum mechanics (real, complex, or quaternionic) is determined by the topology of the compact dimensions (Riemannian, Kähler, or hyperkähler respectively), making laboratory quantum experiments probes of extra-dimensional geometry. CPT symmetry corresponds to orientation-invariance of the compact manifold, connecting discrete symmetry tests to the topology of the extra dimensions. The theorem requires no physical assumptions beyond the existence of inaccessible compact Kähler dimensions. It applies to any number of dimensions, any compact Kähler geometry, and any deterministic dynamics. The paper concludes that quantum mechanics is not a law of nature but a law of perspective — the second such law in physics, following relativity. Where relativity revealed that the separation of spacetime into space and time is observer-dependent, this work shows that the separation of dynamics into deterministic and probabilistic is equally observer-dependent. Originally submitted to Foundations of Physics on March 16, 2026