Stephen Hawking, Leonard Mlodinow. The shortest history of time (№ 8704)

If, indeed, there is no comprehensive physical theory that governs everything, then it must be assumed that it determines our actions. However, it makes it so that its consequences cannot be predicability for such a complex organism as a human being, and, in addition, it includes a certain element of randomness, the corresponding quantum mechanical effects. This allows us to say that our statements about human free will stem from the impossibility to predict what he will do. However, if a person will fly on a space ship and return before I ever went, we could predict that he or she will do it, because it will be part of recorded history. Thus, in this situation, the time traveler would not have free will in any sense.