The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing? – 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