Galactic Delayed Signal Hypothesis

This preprint investigates whether an encoded electromagnetic transmission could leave Earth, reflect from a natural planetary or lunar body, and return to Earth at its future position. It considers practical scientific uses, deliberately delayed cultural messages, and the more demanding possibility of preserving knowledge for future societies. The study combines moving-target geometry, optical and radio link calculations, receiver requirements, and information-recovery models. It compares green and infrared lasers, distributed transmitters, beam coverage, energy requirements, and error-correcting codes. A nearby interstellar case uses Proxima b under explicitly stated assumptions about its unknown reflecting properties. A separate reanalysis of published lunar-radio observations provides a measured check of known-waveform processing. The results distinguish present-day capabilities, idealized modeled configurations, and conditional future engineering requirements. They identify possible improvements while showing substantial unresolved limits in targeting, transmitted energy, background rejection, and future receiver availability. No working interstellar archive, ancient transmission, or previously unknown astronomical signal is claimed. The manuscript distinguishes signal detection and recognition of a known message from recovery of previously unknown information. Accompanying code, calculation outputs, and supporting data document the methods and assumptions for reproducibility. This is a preprint and has not undergone external peer review. The manuscript is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). The original software files identified in the package license manifests are released under the MIT License; third-party data and previously licensed material retain their stated terms.