For asymptotically flat universes, Einstein and others salvage conservation of energy by introducing a specific global gravitational potential energy that cancels out mass-energy changes triggered by spacetime expansion or contraction. This global energy has no well-defined density and cannot technically be applied to a non-asymptotically flat universe; however, for practical purposes this can be finessed, and so by this view, energy is conserved in our universe. Alan Guth stated that the universe might be "the ultimate free lunch", and theorized that, when accounting for gravitational potential energy, the net energy of the Universe is zero.
For asymptotically flat universes Einstein and others salvage conservation of energy by introducing a specific global gravitational potential energy that cancels out mass-energy changes triggered by spacetime expansion or contraction This global energy has no well-defined density and cannot technically be applied to a non-asymptotically flat universe; however for practical purposes this can be finessed and so by this view energy is conserved in our universe Alan Guth stated that the universe might be "the ultimate free lunch" and theorized that when accounting for gravitational potential energy the net energy of the Universe is zero