Gravitational binding sets cosmic reachability

Whether two objects are gravitationally bound (mutually trapped in orbits or potentials) — not merely physically close — determines if they will remain accessible to one another as space expands. In an accelerating Universe this boundary separates the future island that remains reachable from everything that will recede beyond our horizon. — That boundary reframes public discussion about the far future (astronomical isolation, the limits of interstellar travel, and the meaning of cosmic community) and grounds policy‑adjacent conversations about long‑term space priorities and storytelling.