You wait years for a book on the interpretations of quantum theory and then they appear in droves. In reality though, it's a good thing - each of them has brought its own slant and approach, and never more so than in Einstein's Unfinished Revolution from theoretical physicist Lee Smolin. Although Smolin takes us on a tour of the best-known interpretations, he sets out his intention from the beginning - he is a realist and wants an interpretation that incorporates realism. That might not seem much of an ask - surely everyone in science wants realism? - until you realise that the long-prevailing approach, the Copenhagen interpretation is anti-realist. This is because we're dealing with a particularly theoretical physics view of the world. It's not that those who have held the Copenhagen interpretation don't think the world as a whole is real. Rather that the requirement that, say, a quantum particle has no location, just probabilities, until it interacts with...