The Cosmic Return Stroke: Unique Eigenstate Selection and the First-Passage Resolution of the Fermi Paradox

We present a foundational resolution to the Fermi Paradox derived directly from Time-Symmetric Quantum Darwinism (TSQD). In our preceding work, we demonstrated that the universe bootstraps a unique, self-consistent final boundary condition as the non-degenerate dominant eigenstate of a retro-causal pointer-selection operator. Here, we prove that the non-degeneracy of this final state imposes a strict "winner-take-all" First-Passage Theorem on macroscopic evolutionary trajectories. Modeling cosmic history selection as dielectric breakdown in Hilbert space—where forward-time quantum branches act as stepped leaders exploring candidate planetary biospheres and the backward-propagating final boundary acts as the return stroke—we show that classical reality requires only a single closed amplification loop between the initial state and the final boundary. The first evolutionary lineage to cross the macroscopic Quantum Darwinist amplification threshold completes the circuit, triggering a retro-causal return stroke that locks in that single path and drains the probability amplitude from all competing stepped leaders. Because the realized eigenstate threads directly through abiogenesis on Earth and humanity, other exoplanetary branches never closed the loop on our timeline. Consequently, there are no concurrent extraterrestrial civilizations: humanity is not merely one observer among many, but the specific first-passage trajectory that anchored the cosmic eigenstate.