The radiation left over from the Big Bang is the same as that in your microwave oven but very much less powerful. It would heat your pizza only to minus 271.3*C – not much good for defrosting the pizza, let alone cooking it. – 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

