Return Theory (RT) — SETI, Quantitative Observability Filters for Extraterrestrial Signal Searches

This work presents a standalone observational framework for SETI grounded in Return Theory (RT). Rather than assuming that the absence of detected signals implies the absence of extraterrestrial emitters, this paper reframes SETI null results as a problem of observability. Within RT, observation is treated as a geometric time-projection from shell-time to observer-time. Building on this principle, the paper introduces a set of quantitative, data-level observability filters: the Narrative Stability Index (NSI), Phase Coherence Measure (PCM), Bounded Variability Ratio (BVR), and Projection Robustness Test (PRT). These criteria operate directly on time–frequency data, require no assumptions about extraterrestrial biology, technology, or intent, and introduce no new physical dynamics. They are fully compatible with existing SETI pipelines and can be applied retroactively to archival datasets. This document complements the cosmological and observational foundations of Return Theory by extending its projection logic to the problem of extraterrestrial signal detection, offering a principled reinterpretation of the long-standing “Great Silence” as an observational accessibility issue rather than an existential one. Related framework: Return Theory (RT) Reference: Zenodo DOI: 10.5281/zenodo.17857410