This book is the closest thing to my favorite book -- mostly because I can't really remember anything else I've read -- but I've read it countless number of times and so I'm really glad I reread it again.
It's a tale that weaves physics and 14th century history together into one story with action and knights and squires and ladies of the court and all of those awesome things that I love with historical stories into one.
I guess the most difficult concept in this book is that time travel is essentially impossible, that because time is continuous, it cannot move and you can't travel to a different time as if it's a location. The physics was kind of difficult to swallow because I know nothing about quantum mechanics, but oh god, it was so interesting. *____* I don't want to spoil anything because it's kind of important to the story, but there's so much adventure and imagery and it's the best thing.