The problem with time travel

I've always loved second hand bookshops, particularly the science fiction/fantasy section. These shops are often as well-stocked and have as many quality titles as a regular bookshop. In the past though, I've tended to avoid time-travel titles. Look I can buy giant three headed ogres, faster than light travel, and mental telepathy. But time travel never gets past the suspension of disbelief hurdle for me. I guess that part of the problem is that standard views of time travel violate my understanding of both how the past works, and how the future works. What I have only recently realized is that, firstly, I can suspend disblief on the time travel front, and secondly, much science fiction is more sophisticated in its treatment of time than I realized.
Standard 'hollywood' time travel is often of the back-to-the-future variety: the protagonist travels backward to change a key event in the past. In the case of Back to the Future, Marty McFly (played by Michael J Fox) visits an eccentric professor, accidentally travels back in time, and stops his parents from meeting each other. With the professor's help, he must travel back again and undo the mistake, or he will cease to exist.
In The Terminator, the bad guys travel back, and they travel back from the future to the present, but the concept is the same. We learn that there is a war in the future between humans and robots. The leader of the human resistance is a man called John Connor. The robots send a robot assassin - a "terminator" - back in time to kill Connor's mother, Sarah, before she can give birth to the future leader (the terminator robot was played by Arnold Schwarzenegger). The humans also send a man, Kyle Reese, back in time, to stop the terminator. Thus the stage is set for a thrilling damsel in distress story, with Sarah relentlessly pursued by an indestructible robot, saved at every turn in the nick of time by the resourceful Reese. There were two sequels, each with exactly the same plot.
Back to the Future is light-hearted fun, while The Terminator is a tense thriller. Both rely on exactly the same time travel concept: travelling back into the past to change the present in one's favor. Of course, this opens a hornet's nest of questions, such as "what will happen if I meet myself?", "if I cause someone to not exist, is there a parallel universe where they still exist?" and so forth. Back to the Future, and it's sequels (yes it has two as well) actually explores these and other questions in some detail. It solves many problems by creating a parallel time-line every time the past is changed. This actually leads to some rather convoluted plots in the sequels as the heroes jump back and forth through a maze of timelines that they have created.
The "go into the past to change the present" concept was also employed in at least two Star Trek movies (Star Trek IV: The Voyage Home and Star Trek: First Contact), and has made numerous other appearances on the large and small screen. It was boredom with this conceit that put me off time travel science fiction. However, when I started reading time travel books, written by classic authors such as Clifford Simak, Brian Aldiss, and others, I discovered that the treatment of time travel is much more diverse in the written sci-fi literature than the ubiquity of the go-back-to-save-the-present plotline lead me to believe.
For instance, in Cryptozoic, by Aldiss, humans can go back in time, but only as observers. They can see events unfold around them but they cannot alter them. They can also see and interact with other time travellers. The book is about an artist who has travelled back to the cryptozoic era for inspiration, but has spent so much time in time travel that he is going mad. There is also a sinister sub-plot about him being chased by agents of a shadowy organization (or is that just his brain-addled fantasy?).
In Simak's Tomorrow's people, portals open from the future and people start walking out in the thousands. They are escaping from an apocalyptic confrontation with aliens that are all-powerful and bent on wiping out humanity. There is no hope, so they escape into the past... literally. They stop by in the present on their way back to a distant past millions of years ago, long before the advent of humans.
Phillip K Dick's Now Wait for Last Year involves a drug that can allow you to travel backwards and forwards through time. However the drug is very addictive, and may send you insane. Now wait for last year explores numerous permutations of time-travel problems, from meeting oneself, through to changing the past and the future, and encountering numerous paradoxes.
For me, the problem is with plots that involve travelling into the future, starting right back with Wells' The Time Machine. For the very concept of visiting the future demonstrates a lack of understanding of what the future is: it is that which has not yet been created. Not having been created, it therefore does not exist. There is no future to visit. Visiting the future uses a defunct model of time and space: strict determinism. Once, learned people, scientists, philosophers, theologans and such, believed that the future was fixed and immutable. The principles of cause and effect made it so. If we understood the laws of physics well enough, and we knew everything about the present down to the tiniest detail, then we would be able to predict the future as easily as a professional snooker player can predict which pocket the ball will fall into. Physicists aimed to predict the weather and other mysterious events. Theologans talked of predestination. Philosophers talked of free will and its absense in a deterministic universe.
That concept of the future died with quantum mechanics. Even if you know everything there is to know, any event is still probabilistic. Those uncertainties add up over lots of events, so that in the end, all that is ahead is unknown. Schroedinger's cat is both alive and dead.
Similarly, visiting the past and talking to people in the past shows a lack of understanding of what the past is. The past is fixed, the future fluid. Science fiction that acknowledges this, such as Aldiss' Cryptozoic, can actually be more surprising and thought-provoking than stories that do not, such as Now Wait for Last Year, The Terminator, or Back to The Future. Ignore these fundamental truths about time and you end up with contradictions, paradoxes, and hopelessly messy plots. Such stories may be fun, but they are unconvincing, and therefore, ultimately, unsatisfying.