Here is something interesting. I am reading the first three books of M. (Michael) R. Forbes' War Eternal series. As a plot device he uses a time loop. It is a similar concept to a causal loop. In a causal loop nothing changes nor can it change. A time loop, on the other hand, loops back on itself and while everything starts over again exactly as before the future can be changed - if there is a catalyst (be it a person or event) to cause that change. Then the loop resets to the new future.
In his universe, time cannot go backwards, only forwards. So, in order for someone from the future to "go back" he/she must go forward following the time loop until they get to the next past iteration, "The future past". Each successive loop leaves a wee bit of memory from the last loop. Interesting concept, kind of like remembering past lives, deja vu or the like. Kind of reminds me of the movie title Back to the Future.
Right now, this is mostly a plot device, but there are some scientific papers speculating on the nature of spacetime that address the possibility.
Back to the book series, I do like the characters and the story. I had read the first book a few years ago and thought it was interesting but not interesting enough to go on with the series. I am glad I reread the first, Starship Eternal. I am guessing here, but there are things in this rereading that I swear weren't in the original I read. A bit more explanation I think, and things that certainly helped me to understand the broader nature of the series. I can't imagine that I missed that much reading it the first time. But hey, like I said, I read it several years ago. Forbes recently published the seventh and last of this series. I am now well into the next book, The Fall of Liberty.
