Thrice Upon a Time

Most time-travel stories are about people travelling back and forth in time, which is traditionally regarded as science fiction, although it's really fantasy because it doesn't seem scientifically plausible.

This story is about people exploiting an obscure feature of particle physics in order to send information (e-mail, in effect) back in time. That obscure feature of particle physics doesn't actually exist, as far as I know; but particle physics is so weird already that it seems excusable to add another minor oddity to it for the sake of a story.

Hogan makes quite a nice story about the implications and consequences of being able to send information back in time, and I think the book is worth reading. However, be warned:

1. It was apparently aimed at serious amateur physicists, who will be fascinated by lengthy technical discussions of particle physics, nuclear fusion, the nature of time, and (to a lesser extent) 1980-era minicomputer programming. Ordinary mortals must be ready to skim rapidly through all this stuff, which takes up most of the first half of the book. The second half of the book is more exciting, urgent things start to happen, and the technical details are more abbreviated.

2. The characters of the story, and their interactions, are managed competently enough by sf standards, but won't win any prizes for literature.

Overall, if you can digest or ignore all the technical discussions, this is a decent minor sf novel, not a great work of fiction. It's memorable mainly for describing a limited form of time travel that one can almost imagine being feasible, and seriously discussing its implications.