Microphysics Shapes Cosmic Fate

Key unknowns in particle and dark‑sector physics — e.g., whether protons decay, whether dark matter self‑interacts, and whether dark energy is truly constant — are not just esoteric details: each plausible alternative produces qualitatively different end states for galaxies, planets, and radiation over trillions to googol years. Because current observations permit these possibilities, cosmological forecasts (and related science agendas) should treat multiple far‑future scenarios as scientifically open. — Framing the Universe’s fate as contingent on near‑term particle and astrophysics motivates public investment, shapes long‑range scientific priorities, and clarifies why ‘fundamental physics’ matters beyond the lab.