Right, forget any debates about the physicalities of time travel, Just say for a moment that it was possible. What would happen? In our present time, can it be denied that everything that has happened has happened? If you went back in time, your presence in that timeline would alter events no matter how careful you were. Your very existence would change time. These changes would then be present in your own time and you would have memories of them. or would you? During time travel would you disappear from your own time? could you meet your self in the past? or would you cause a shift in everything so that everything is as it was? Here's another question. Would you find anything in the past? Does the old model that everything is repeating itself over and over work? Everything that was there is now here, if you remove yourself from our time then could you garantee that you would end up anywhere at all? What about travel into the future? The future hasn't happened yet, so is there anything there at all? It can be said that when you arrive in the future, it will have happened. But what about the trousers of time? With an infinite number of futures, which one will you land in? and then how do get back to your own time? All questions and no answers, but that's what you are faced with when you start to try and mess with time. The truth is beyond us and always will be.