Source of energy for infinite expansion

Question

I read in several sources that matter, dark matter & dark energy contributes 5%, 26% and 69% of the known universe. Also, I read in a slide deck about Big Bang theory on nobelprize.org that total energy in the universe is not conserved. Then how does universe generates new energy to propel infinite expansion?

Answer 1

The reason that energy is usually conserved in most contexts is that Noether's theorem guarantees that energy is conserved in systems with time translational invariance. But the metric of the universe as a whole is (approximately) the Friedmann–Lemaître–Robertson–Walker metric, which does not have time translational invariance (more precisely, there does not exist a timelike Killing field corresponding to conservation of energy). So there's no reason to expect that energy would be conserved in this context. There's no specific "source" of the new energy.