A fun, fast paced science fiction thriller. I read it in 2 nights and couldn't put it down. The book is about the quantum theory of many worlds which states that all decisions we make throughout our lives basically create branches, and that each possible path through the decision tree can be thought of as a parallel world. And in this book, someone invents a way to switch between these worlds. This was nicely alluded to/foreshadowed in this quote: 
 "I think about all the choices we've made that created this moment. Us sitting here together at this beautiful table. Then I think of all the possible events that could have stopped this moment from ever happening, and it all feels, I don't know..." "What?" "So fragile." Now he becomes thoughtful for a moment. He says finally, "It's terrifying when you consider that every thought we have, every choice we could possibly make, branches into a new world." 
 This book can't be discussed without spoilers. It is a book about choice and regret. Ever regret not chasing the girl of your dreams so you can focus on your career? Well Jason2 made that choice and then did regret it. Clearly the author is trying to tell us to optimize for happiness - to be that second rate physics teacher at a community college if it means you can have a happy life. I'm being snarky because while there is certainly something to that, you also have to have meaning in your life that comes from within. I thought the book was a little shallow on this dimension. In fact, all the characters were fairly shallow. Daniela was the perfect wife. Ryan the perfect antithesis of Jason. Amanda the perfect loyal traveling companion, etc. This, plus the fact that the book was weak on the science are what led me to take a few stars off - but I'd still read it again if I could go back in time - was a very fun and engaging read. 
 If you want to really minimize regret, you have to live your life to avoid it in the first place. Regret can't be hacked, which is kind of the point of the book. My favorite book about regret is Remains of the Day. I do really like the visualization of the decision tree though - that is a powerful concept. 
 "Every moment, every breath, contains a choice. But life is imperfect. We make the wrong choices. So we end up living in a state of perpetual regret, and is there anything worse? I built something that could actually eradicate regret. Let you find worlds where you made the right choice." Daniela says, "Life doesn't work that way. You live with your choices and learn. You don't cheat the system."