The quote on the cover proclaims Hogan the "Dean of hard SF." I'd think Arthur C. Clarke or Larry Niven better fits the title, but reading the book, even if he doesn't head the department, he definitely works there. This novel really does deal with a lot of fascinating and big ideas, and it isn't hand-waving Bat-science either in this book about the concept of the Multiverse. I can't recall ever reading a more lucid explanation of the paradoxes that inspired quantum physics. And from that hard physics foundation, Hogan spins a lot of implications biological, political and spiritual. It's well-written too, even if hardly literary fiction--all the science, for instance, is conveyed without of feeling of infodump. Yet I'm rating this only three stars and putting it in the box of books to sell, give away or throw out. That's not because I would not recommend it to fans of hard science fiction, but I don't feel it's a keeper either. I'd read this before some years ago but couldn't remember one thing about it before rereading. In contrast, decades after reading them, I could remember the characters and events in Herbert's Dune, Robert Heinlein's Starship Troopers, even short stories by Isaac Asimov only by their titles. The main reason this book is getting purged from my collection is that I can't imagine I'll want to read it again. Its writing doesn't evoke writer's envy, it doesn't have characters or a world I love such as with Lois Bujold's Vorkosigan Saga or Anne McCaffrey's Pern such as it would make a good comfort read. It's an entertaining book--just not one I could read over and over again or that I see as exceptional--and it wasn't as fun to read as the Hogan book I read just before this one, Realtime Interrupt (or Code of the Lifemaker, which I later reread).