The First-Fluctuation Hypothesis: The Monomedium Era, the Onset of the Universe's Expansion and the Origin of Matter

This paper is part of the SRDP (Self-Replication of Dark Particles) programme. It is a conceptual note with no new calculations. Our founding assumption is "nothing comes from nothing": something has always existed, and that something is the monomedium — a homogeneous continuous medium not composed of particles. What is eternal is an equilibrium, unchanging on average (like a gas: molecules move, pressure stays constant), not literally. The monomedium era is an eternal equilibrium of a vacuum-like medium; the simplest version is a stable "parent" vacuum, not our present one (ours is probably metastable). The first-fluctuation hypothesis: a rare fluctuation, the first for our world rather than for the monomedium, turned a region of the medium into a Gliner "heavy vacuum" (p = −ρ), and inflation began; self-replication starts with it. Of three routes to a beginning (from equilibrium, evolution, "nothing"), a literally unchanging state with a single event is excluded; evolution without a beginning is excluded in the models considered; creation "from nothing" is not refuted but not chosen, on principle. In equilibrium "why not earlier" loses its meaning; the measure problem ("Boltzmann brains") remains open. Continuations on an equal footing: A — our world is born closed (Ω_k < 0); B — many bubble universes, ours open or practically flat (Ω_k ≥ 0). The fixed point "production = dilution" of version 2 is refuted. Status: the monomedium era and the first-fluctuation hypothesis — not established; the literal form of the earlier hypothesis — refuted.