Does God play dice?

Einstein was one of the founders of quantum mechanics, yet he disliked the randomness that lies at the heart of the theory. God does not, he famously said, play dice. However, quantum theory has survived a century of experimental tests, although it has yet to be reconciled with another of Einstein's great discoveries – the general theory of relativity. Below four theorists – Gerard 't Hooft, Edward Witten, Fay Dowker and Paul Davies– outline their views on the current status of quantum theory and the way forward