Infinity- without beginning or ending is a different dimension of existence than our 3D existence where we are accustomed to beginnings and endings of things.
Anyway the Law of the Conservation of Energy/Matter is scientific proof that energy/matter cannot be created or terminally destroyed. A universe 'big bangs' into existence then eventually 'big crunches' into a single black hole then big bangs again into another new universe. Repeat infinitely without beginning or end of time.