The Hilbert Filter Hypothesis: A Quantum-Encoded Resolution to the Fermi Paradox

The search for extraterrestrial intelligence (SETI) has largely focused on detecting classical electromagnetic emissions or large-scale astroengineering. However, this approach may overlook a class of signals accessible only to civilisations that have mastered quantum information science. We propose the Hilbert Filter Hypothesis: that advanced civilizations may encode interstellar messages in the entanglement structure of quantum states, such that meaningful information only emerges when measured in the correct quantum basis. Such encoding acts as a natural epistemic filter, allowing only sufficiently mature civilisations to detect and interpret these signals. Recent developments in cyclically symmetric entangled states (e.g., W-states with K-value labelling) support the feasibility of such communication. We outline an observational strategy and discuss implications for SETI, technosignature searches, and interstellar epistemology.