From Orion’s Arm, Why Time Travel Would Destroy the Universe.
(Hypothesis #4): The Radical Rewrite conjecture; in this scenario you can change your own history, which means the whole of time is mutable and can be shaped to one’s own whim. If there is only one universe, history becomes fluid. You might go back and change history, then another time traveler will change it again almost immediately, and the present will be an ever-changing kaleidoscope, with a different President or Prime Minister every day; you will go to sleep in a mansion, and wake up in a mobile home; your car will change from a Buick to a Volkswagen while you are driving it. What is worse, you will not be aware of such changes happening – you will suddenly have a whole new past and a new set of memories created by a meddling time traveler long ago. In some versions of this scenario, each time traveler which goes back in time effectively destroys his or her own future existence, and becomes orphaned in time.
Such a lack of continuity will invoke the Chronological Protection Conjecture: the universe will morph and mutate until it reaches a history in which time travel has never been invented, ever, at any time in the past or future. This is the only stable state for the universe, the one we are in now. The CPC has been proposed by many people, including Hawking, Asimov and Larry Niven. =read full article=