Umbo: “‘Because none of that has happened yet, so now it won’t,’ said Umbo. So why do you need to deliver the messages this time at all?” “Loaf: “…you learned how to go back in time … delivered the warnings, and now everything is happening differently. Present-Umbo wants to figure out how to do it so he makes sure Future-Umbo knows how to do it: What follows is typical dialogue in the book, occurring in this exchange between the characters named Loaf and Umbo, after Future-Umbo went back in time to deliver a warning to the character Rigg before disaster could strike. Somewhere in all of this there is a story, but to me, it got almost totally loss in all the craziness. Now, imagine a whole book of over 650 pages that makes it seem like you are caught inside such a math puzzle for the entire book! A book that has to explain to you in an appendix such facts as “the ship made it through that first jump … 31 light years from Earth times 19 squared”…! A book all about characters who travel back and forth in time but are always arguing about whether they have influenced each other in the past or in the future, or whether they are making time slow down or time speed-up, or if the current incarnation of the character needs the future self to go back and interact with the past self, and did that mean the past really happened or never had happened or never would happen or….? Are you screaming yet? Because I was!!!

How many kilometers does the fly travel before getting squashed in the collision of the two trains?” Upon reaching the other train, the fly turns around and continues towards the first train. A fly starting out at the front of one train, flies towards the other at a speed of 75 km/h. Remember those math problems from school that gave so many of us nightmares? Like, “Two trains are on the same track a distance 100 km apart heading towards one another, each at a speed of 50 km/h.

Pathfinder by Orson Scott Card