Misner space

Charles Misner discovered a simplified universe that could be applicable to understanding time travel. This is called Misner space and a good way to understand it is by picturing the room you are sitting in, as the entire universe. Opposite walls would be identified with each other. If you enter one wall, you will immediately emerge from the other wall. The ceiling is also identified with the floor. You would also see a carbon copy of your backside, looking through the transparent walls. However, you would never see your face, only a carbon copy of the back of your head. The reason Misner space is useful for our conversations right now about time travel, is that, it has the same topological properties as a wormhole. However, Misner space is much easier to work with mathematically. If we could make the walls move in a Misner space, time travel could be theoretically possible. You could travel so fast that you actually travel back in time. According to Hawking, the left and right wall would be representative of the two mouths of the wormhole. However, there is an instability: if a beam of light goes from the right wall to the left wall, it would gain energy every time it emerges from the right wall, until has reached infinite energy, which is impossible.