A Direct Test of Gravitational Universality Across Interaction Sectors Using Optical and $^{229}\text{Th}$ Nuclear Clocks

The equivalence principle is a foundational pillar of General Relativity (GR), requiring that gravitational time dilation depends exclusively on the spacetime metric. While this metric universality has been confirmed to sub-centimeter resolution using optical lattice clocks, every existing precision test has compared oscillators governed entirely by the electromagnetic interaction. Consequently, the structural response of an oscillator governed by the strong nuclear force to a changing gravitational potential remains unprobed, leaving a fundamental gap in the empirical record. To assess possible non-geometric contributions to time dilation, we introduce a framework linking cosmological gravitational effects to nuclear mass-defect transformations. Building on recent proposals that fission and fusion scission events generate localized, pre-thermal Scission Pressure Pulses (SPPs) [1, 2], we posit that mass-defect products from pervasive cosmic nuclear events undergo a phase transition into an ultra-dilute, non-baryonic physical substrate. The continuous accumulation of this substrate forms a Gravitationally Variable Density Medium (GVDM) around massive bodies. If time dilation emerges from a potential-energy coupling between a quantum oscillator and the local medium density rather than from spacetime curvature, oscillators governed by different fundamental forces must couple differently, yielding differential fractional frequency shifts. The $^{229}\text{Th}$ nuclear clock provides a uniquely suited probe for this requirement. Its ~8.4 eV isomeric transition constitutes a genuine strong-force oscillator with entirely intra-nuclear dynamics. We propose an experimental protocol to continuously measure the frequency ratio $R = f_{nuc}/f_{opt}$ of a co-located optical lattice clock and a $^{229}\text{Th}$ nuclear clock. Measurements would be conducted across an altitude displacement of ~3000 m, as well as statically over a six-month period. This static measurement exploits the varying solar gravitational potential caused by Earth’s orbital eccentricity, thereby isolating pure potential-energy coupling from transport systematics. This protocol presents a strictly falsifiable dichotomy. Metric universality unambiguously requires a null shift ($\Delta R = 0$). Observing this null shift would definitively extend GR’s empirical domain to the strong-force sector for the first time. Conversely, observing the mass-ratio-derived predicted deviation ($\Delta R/R \sim 10^{-17}$ to $10^{-18}$) would falsify metric universality, providing direct evidence for a physical, mass-defect-generated gravitational medium. References: [1] George J. "Three Falsifiable Experimental Tests of a Sub-Picosecond Scission Pressure Pulse: Mechanistic Insights into High Burnup Structure in Irradiated $UO_{2}$". Zenodo. doi: 10.5281/zenodo.20125607. [2] George J. "Pre-thermal mechanical energy partition in fusion events: A falsifiable XFEL diagnostic for primary damage state modeling". Zenodo. doi: 10.5281/zenodo.20673613.