The Fluid Cosmic Crystal Theory (FCCT) proposes that the vacuum may be effectively described as a structured, elastic, and dissipative medium rather than an empty geometric background. Within this framework, gravitational and cosmological phenomena are interpreted not only as manifestations of spacetime curvature, but also as emergent responses of an underlying substrate exhibiting mechanical and memory-like properties. The primary FCCT documents establish the conceptual and phenomenological basis of this approach. However, in order to transition from theoretical formulation to empirical relevance, it is necessary to examine whether observable data contain signatures that are at least consistent with such a structured-medium interpretation. This technical appendix is therefore introduced as an exploratory extension of the FCCT research program. Its purpose is not to provide definitive validation, but to investigate whether interferometric strain data—specifically from the LIGO Hanford (H1) and Livingston (L1) observatories—exhibit correlated spectral features that may motivate further study under the FCCT framework. The analysis presented herein focuses on cross-coherence structures within a constrained observational window centered on the GW150914 event. Particular attention is given to persistent spectral features that appear across detectors, as these may indicate either shared instrumental effects or nontrivial correlated responses. While certain features correspond to known calibration or environmental sources, additional structures emerge that are not immediately classified and therefore warrant further examination. It is essential to emphasize that the results reported in this appendix are preliminary and exploratory in nature. No claim of definitive detection of a structured vacuum is made. Instead, the findings are presented as empirical prompts that motivate a more rigorous program of statistical validation, multi-event replication, and theoretical refinement. In this sense, the appendix should be understood as a bridge between conceptual theory and observational inquiry. It defines a testable interface through which FCCT may be evaluated against real data, while maintaining methodological caution appropriate to the current level of evidence. The broader objective is to establish whether a consistent, reproducible relationship can be identified between interferometric observables and the hypothesized viscoelastic properties of spacetime. Achieving this will require not only expanded datasets and improved statistical treatment, but also the development of predictive structures within FCCT capable of specifying where and how such signatures should arise. Accordingly, this document represents an initial step in that direction: a constrained, data-informed exploration designed to open a pathway toward empirical assessment, rather than to close the question of physical interpretation.
Boris Calderon Martinez (Sun,) studied this question.