Apparent Superluminal Scales and Hierarchical Spacetime: A Phenomenological STLT Case Study of AT 2026abck

The JWST/NEXUS survey has reported a candidate young transient, AT 2026abck, at redshift : the rest-frame time from the last non-detection to the discovery is less than about 12 days, and the authors estimate that it was observed about 4–10 rest-frame days after explosion; model fits give a temperature of about 17,000 K and a radius of about 46 AU, overall supporting a core-collapse supernova candidate. This paper does not reject that classical interpretation. Instead, it raises a conceptual question: to what physical quantity does the "apparent superluminal number" constructed from a cosmological distance and an event timescale actually belong? Standard cosmology first requires distinguishing a distance–time ratio from a material expansion velocity; the Spacetime Ladder Theory (STLT) further proposes that such an apparent superluminal quantity can serve as a candidate observable of projections from different hierarchical levels of spacetime. This paper makes clear that: the material-end expansion velocity remains below ; the apparent distance–time ratio is used only to construct a phenomenological scale; and the three-tier velocity spectrum of STLT is a theoretical hypothesis, not a result measured from this single event. On this basis, the paper proposes a search scheme for "higher-level spacetime perturbations" (HLSPs) and gives falsifiable conditions based on multi-messenger time delays, non-tensor polarizations, and independent transient events. AT 2026abck therefore serves as a methodological case study, not as proof of the existence of a dark-matter layer.