If space is filled with virtual particles, then it would seem that as the volume of space increases, the rate of production of virtual particles would increase. Where does that energy come from? It would seem that energy is not actually conserved by the universe as a whole - that energy is conserved only within localized systems within the universe. Do we need to be careful about inferring physical laws on the universe as a whole? Perhaps nothing need be conserved by the universe as a whole.