The surprising answer is: nobody knows. Physicists, despite trying for almost a century to rule it out, have so far failed. The known laws of physics do not forbid time travel. In fact, they appear to make it easy - at least in principle.
28.000 light years away from Earth, towards the center of our Milky Way, an unexpectedly mighty hurricane blows around a tiny black hole. It is the strongest wind ever observed by astronomers and a great surprise because these pushed off particles exceed the speed of 32 million k.p.h