An independent, optical-domain test of the Temporal Equivalence Principle (TEP) is presented using 11 years (2015–2025) of Satellite Laser Ranging (SLR) data from passive ILRS geodetic satellites (LAGEOS-1/2 and Etalon-1/2). This analysis constrains "clock-artifact" explanations by employing two-way optical ranging to passive retroreflectors—a methodology orthogonal to the microwave measurements of active atomic clocks used in Global Navigation Satellite Systems (GNSS). Under strict 5-minute contemporaneous binning, distance-binned mean pass-correlations fluctuate with high variance. However, widening the overlap window to 15 minutes (thereby increasing multi-station overlap) reveals statistically significant, distance-structured inter-station correlations (Fisher-combined ²=15. 35 with 4 d. o. f. ; p=0. 0040) under a family-wise circular-shift test. This signal is driven primarily by LAGEOS-2 (p=0. 0005), which exhibits a strong negative correlation (r -0. 59) in the 5, 000–7, 500 km distance bin, whereas LAGEOS-1 remains consistent with the null hypothesis (p 0. 93). Although observation counts and temporal overlap are comparable, this asymmetry likely reflects a combination of orbital geometry—LAGEOS-2's prograde 52. 6^ orbit versus LAGEOS-1's retrograde 109. 8^ orbit—and small-number statistics in the critical distance bin. To validate this finding with more robust statistics, a daily-aggregation analysis (N=190 station pairs) was performed. This confirmed a subtler but statistically significant negative correlation at shorter ranges (500–1, 000 km, p=0. 017), suggesting a persistent global background structure independent of the high-amplitude LAGEOS-2 events. The observation of matching low-frequency structure in a system devoid of active clocks and microwave propagation challenges receiver electronics, clock steering, and ionospheric modeling errors as complete explanations. While current network sparsity limits testing to the conformal sector, this work demonstrates SLR as an independent, technology-orthogonal line of evidence for TEP phenomenology. Website: https: //mlsmawfield. com/tep/slr/Code Availability: https: //github. com/matthewsmawfield/TEP-SLR Keywords: temporal equivalence principle – Satellite Laser Ranging – SLR – LAGEOS – atomic clocks – modified gravity – spatial correlations Open Science Statement: This work is a preprint and is open to community review, ideas, and collaboration. All materials required for full reproducibility—including data downloads, analysis scripts, code, and manuscripts—are open-source. Feedback and contributions to further test these results are welcome.
Matthew Lukin Smawfield (Tue,) studied this question.