A ring wormhole might be a time portal
Wormholes are often thought of as tunnels through space-time with black holes for entrances, but they could theoretically be flat instead, like a door into another location or even another universe. These are known as “ring wormholes”, and in some cases they could also become time machines.
Ring wormholes, first proposed in 2016, are made up of a string of exotic matter with negative energy – a property that is possible due to quantum effects, but only, as far as we know, …