 Because worldliness can wrap around and around the cylinder, \(OP(q)=M\) for any event \(q\). This allows for great freedom in choosing Bob’s worldline \(\gamma\). In fact, we can choose it so that the total acceleration is zero – no fuel is needed to traverse it. Moreover, we can choose it so that there is also no divergent blueshift phenomenon (see Earman and Norton 1993). But, alas, we have a new problem: the spacetime is acausal. A worldline can start and end at the same event allowing for a type of “time travel”. It is unclear if spacetimes allowing for time travel are physically reasonable (see Smeenk and Wüthrich 2011). It turns out that more complicated examples can be constructed which avoid all the potential problems mentioned so far and more (Manchak 2010). But such examples contain spacetime “holes” which may not be physically reasonable (Manchak 2009; Doboszewski 2019). More work is needed to see if such problems can also be overcome. 