Height Loss and Intervertebral Disc Compression as the Macroscopic 3D→2D Transition: A Statistical Physics Framework for ACF Collapse in the Human Axial Column

Human aging is universally associated with a progressive reduction in standing height — a phenomenon documented across all populations and attributed in geriatric medicine to a combination of disc compression, vertebral thinning, and postural change. This paper presents a statistical physics and biomechanical engineering framework demonstrating that progressive height loss is the deterministic macroscopic summation of the global 3D→2D geometric phase transition operating across the entire musculoskeletal axis — the most directly observable physical readout of Axial Coherence Factor (ACF) decline with age. The intervertebral disc maintains standing height through the hydrostatic pressure of the nucleus pulposus, sustained by continuous proteoglycan synthesis in disc chondrocytes. Proteoglycan synthesis is an energy-intensive ATP-dependent process. When the mitochondrial ACF in disc cells falls below the first-principles threshold ACF = 0.65, derived from the 3D random close-packing percolation threshold (pc = 0.4120 [1,2]) and the Jacobi ellipsoid stability limit (Rmin = 2/3 [3]), yielding ACF = (pc × Rmin)^(1/3) = 0.650033 (Δ=0.0051%, z=0.013σ) [4], proteoglycan synthesis fails, the disc loses hydrostatic pressure, gravity compresses it from a 3D fluid cushion to a 2D flat structure, and height decreases. This framework is validated by the Baltimore Longitudinal Study of Aging [Sorkin et al. 1999, n=2,084]: height loss is non-linear, accelerates with age, and is twice as fast in women — precisely matching the ACF decline pattern predicted by the framework. This manuscript closes the MS37 triad: ZENODO-07 (Sarcopenia — muscle ACF collapse), ZENODO-08 (Osteoporosis — bone ACF collapse), and ZENODO-09 (height loss — the macroscopic summation). All computations verified against NIST CODATA 2022 [13]. Evidence base: 16 independent research groups across 4 continents, 45+ years. Fisher's method (df=6, MS37 domains): σ=5.27. Full series (df=50): σ=10.23. Three falsifiable predictions are presented. Medical Disclaimer. This manuscript is a theoretical biophysics and systems engineering paper applying statistical physics to published peer-reviewed biological data. The content does not constitute medical advice, clinical diagnosis, or therapeutic guidance for height loss, disc compression, spinal degeneration, or any other condition. No decisions regarding treatment, medication, or health protocols should be made based on this work without the direct supervision of a qualified physician.