Description This paper presents a self-contained solution to the matter–antimatter asymmetry problem within a classical ether field framework. The ether field possesses an asymmetric self-interaction, giving rise to two non‑degenerate states: a high‑density state (matter) and a low‑density state (antimatter). A thermal phase transition in the early universe favours the high‑density state, naturally producing a net matter excess that matches the observed cosmic asymmetry. A key consequence of the model is that any region of the ether with lower density than its surroundings experiences repulsive gravity. All calculations are performed analytically and link the asymmetry directly to the overall scale of the universe.