Under suitable conditions near infinity, we prove a no breathers theorem in the spirit of Ivey-Perelman for some noncompact Ricci flows. These include Ricci flows on asymptotically flat (AF) manifolds with positive scalar curvature. Theoretical physicists have used these kind of Ricci flows as models for  the evolution of the Universe (in their mind). Our result confirms an expectation of theirs that the world sheets  are irreversible (世界层非轮回）.