It is no good getting furious if you get stuck. What I do is keep thinking about the problem but work on something else. Sometimes it is years before I see the way forward. In the case of information loss and black holes, it was 29 years. – Stephen Hawking
Time travel used to be thought of as just science fiction, but Einsteins general theory of relativity allows for the possibility that we could warp space-time so much that you could go off in a rocket and return before you set out. – Stephen Hawking