What some of you are failing to realize is that time travel is only possible if time itself is non-linear. If time is non-linear then all time has already happened and is simply being replayed over and over again. So the traveling through time itself would happen in the same way over and over again. Time would have conformed itself to the traveling - it would have to because the simple act of traveling through time would, necessarily, alter the time traveled to. It would create another variable. That variable would always have had to exist every time that particular point in time happens.
Many of you talk like, yeah it is possible, we just haven't invented it yet. But it would HAVE to already exist. Otherwise you are looking at it from the viewpoint that we in "present time" are going through all of this for the first time, which would not be possible if time is non-linear. If time is non-linear this has all been done and is just on an "endless loop," which would mean that it could have NEVER happened for the "first" time. In other words, we would have no free will and not truly be making our own decisions as all of these decisions have already played out endlessly.
The THEORY of relativity, et al is just that... a theory. Some of you are SURE that it is fact, just like many used to be SURE that the world was flat and the earth revolved around the sun. We now know that those facts (theories) are not true. Yes, Einstien was quite smart but that does not mean the man was right 100% of the time. He was simply postulating theories based on "facts" known.
Long story short, if time is non-linear then time travel already exists, if it can exist at all... it HAS to. If it already exists then it HAS to be built into the time continuum. If that is the case then nothing can change what has, or is going to, happen as all of this is simply on an endless loop and time travel is already built into that loop. So there is no "going back and changing" this and that because if it was going to happen it would have already happened due to the endless loop. Hence whether time travlel is possible or not, it is a non-issue because the act itself is built into time and cannot alter time as it has all already happened.
The books out there do have some cute ideas based on theory but the simple fact of the matter is, if it can happen it is not going to change anything anyway because if it is possible then it has all already played out.
I realize I might be going over some of your heads, not meaning to sound condescending. Oh well, I guess I can always go back through time and edit this anyway.