Wormholes and Ringholes in a Dark-Energy Universe

The effects that the present accelerating expansion of the universe has on the size and shape of Lorentzian wormholes and ringholes are considered. It is shown that, quite similarly to how it occurs for inflating wormholes, relative to the initial embedding-space coordinate system, whereas the shape of the considered holes is always preserved with time, their size is driven by the expansion to increase by a factor which is proportional to the scale factor of the universe. In the case that dark energy is phantom energy, which is not excluded by present constraints on the dark-energy equation of state, that size increase with time becomes quite more remarkable, and a rather speculative scenario is here presented where the big rip can be circumvented by future advanced civilizations by utilizing sufficiently grown up wormholes and ringholes as time machines that shortcut the big-rip singularity.