Time Machines
This seems like an interesting article, but I found it very difficult to read. For example, from the introductory paragraph:This literature equates the possibility of time travel with the existence of closed timelike curves (CTCs) or worldlines for material particles that are smooth, future-directed timelike curves with self-intersections.[3] Since time machines designate devices which bring about the existence of CTCs and thus enable time travel, the paradoxes of time travel are irrelevant for attempted “no-go” results for time machines because these results concern what happens before the emergence of CTCs.[4] This, in our opinion, is fortunate since the paradoxes of time travel are nothing more than a crude way of bringing out the fact that the application of familiar local laws of relativistic physics to a spacetime background which contains CTCs typically requires that consistency constraints on initial data must be met in order for a local solution of the laws to be extendable to a global solution.I'm not sure what the intended audience for this is; combination philosopher physicists? Given that it's on SEP it seems unreasonable to assume that CTCs need no other explanation than that they are smooth, future-directed timelike curves with intersections. I would love it if someone would ELI5 this concept, though.