Time travel stories that make sense?

I've always liked time travel movies. The whole concept itself is fascinating, and like with sci-fi in general, the stories are often quite different from each other, which makes them memorable. Even though many of these movies are quite entertaining, the logic in them almost never stands any closer look.

Three very different time travel movies - Time Machine (2002), Looper (2012) and Primer (2004).

Although the distinction isn't always exactly clear-cut, the ways in which time travel movies impose inconsistency to their universes can be roughly divided into two groups. I can think of only one movie that does a good job at avoiding both of these categories, creating a group of its own, but let's first have a look at the more common groups. The examples given below are spoiler-free, unless revealing the time travel logic type can be considered as spoiling.

1. Fate - These movies state that even though you can interact with the past, you can never change it. 
• Examples: The Time Machine (2002), Lost (2004-2010), Time Traveler's wife (2009), 12 monkeys (1995)
2. Self-adjusting reality - In these movies changes made in the past only have the kind of effect on the future that happens to support the plot.
• Examples: Back to the future 1, 2 and 3 (1985-1990),  The Time Machine (2002), A Sound of Thunder (2005), Kate & Leopold, Bill & Ted's Excellent Adventure (1989)

Neither of these methods of explaining time travel really holds, but I think I prefer the idea of the second group, because the first one inevitably throws free will out of the picture. Nevertheless, how the way of thinking manifests itself in the movie really makes a bigger difference than the core principle of the story. For example the movie Time Traveler's wife (belonging to the group 1) has an interesting concept and is able to build an interesting story. 12 monkeys also only heavily implies the "fate idiology" but doesn't explicitly prove to be so, which make both of them quite good time traveling movies. From the group 2, Kate & Leopold shows a time travel consequence that's equally ridiculous to the episode of Futurama where Fry finds out he's actually his own grandfather due to to time travel. Whereas Futurama's example felt like a funny joke that epitomizes the problems of time travel in fiction, Kate & Leopold just seemed to quickly destroy any hope of finding some logic in the movie's time travel logic.

Back to the future trilogy is filled with problems related to time travel too. One of the most notable problems is the repeated plot device of depicting a photo or a newspaper that transforms as history changes - as if that photo would have been taken were there no-one to take the picture of and as if that newspaper would have been carried around if there was nothing interesting in it, and as if all of this wouldn't cause paradoxes. The series also often changes the future in ways that happens to fit the plot but doesn't change the future in ways that would in fact be unavoidable. The second part of the BTTF series has also at least two additional issues compared to the first and last movie in the trilogy. Still, these movies are undeniable classics in the genre, and even with all their time traveling issues I can't help but love them: they really make a lot out of the concept, they have a real sense of adventure to them, they keep an applicable level of tongue-in-cheek mood and are all around very entertaining.

So what do I find the worst example of a time travel story? Ironically, the movie called  The Time Machine (2002) (loosely based on the original H.G. Wells novel) takes the cake. By adding new content to the original story from 1895, it does a miraculous job of following both the Fate and Conforming reality concepts, a "dynamic fate" of sorts. While the protagonist is obviously able to change occurrences in the past, thus leaving free will somewhat intact, "important" things cannot change, and the universe will fix this. This feels just plain stupid, as it implies that the universe would distinguish small changes from big ones while still basically destroying free will at least partially.

Some one might have guessed my least favorite movie from the ones I've listed would have been Sound of Thunder (that has received very bad scores on imdb). Even though its premise is weird, doesn't make much sense and seriously underlines the idea that time travel only affects certain aspects of reality, its inner logic kind of holds: the viewer is given the premise early on, and then it just becomes an action ride in a transforming reality.

Of course there are also movies that involve time travel in a different fashion, where cause and effect play a somewhat different role. In Butterfly Effect the difference to most other time traveling stories is that the protagonist interacts with the past as his younger self. This takes the need for doppelgängers and nasty paradoxes out of the picture, which I think makes it a very good time travel movie (I think there was only one insignificant scene where the movie's inner logic failed). The short-lived television series FlashForward (2009) on the other hand is a sad example. I really liked the premise: everyone seeing a short glimpse of the future almost equals the idea of time traveling momentarily into the future. It could have created interesting stories that could have avoided all paradoxes much more easily compared to "traditional" backward time traveling stories. But what did it the series do? It failed miserably by constantly depicting people pursuing their sentimental "flashforwards" that would have never happened had they not seen them 6 months beforehand. It also takes itself far too seriously while doing that. Basically they forced paradox into a premise that wasn't inherently paradoxal!

You might wonder why I didn't include Teminators in the lists. Well, the reason is that although from a certain forgiving perspective the logic of the movies doesn't cause problems, for motivational purposes it seems to follow the logic of group 2. By this I mean that if the Terminator universe would follow the logic of group 3 (to be described below), the machines of the future would have no motivation to send the terminator machines back into the past.

So what is this third group that the Terminator movies almost follow?

3. Alternate timelines - The concept where moving backwards in time always creates an alternate timeline that never affects the original timeline in anyway.
• The only example I can think of: Primer (2004)

Primer succeeds where all other movies fail (or don't even try to succeed in): depicting a universe (or multiverse) where time travel doesn't cause paradoxes nor an obscure absence of free will. This of course doesn't mean that it would be the best in terms of movie entertainment, as that's more of a matter of taste. I agree with all those who find that Primer could have done a better job at delivering the story to the viewer, and accordingly I find eg. Back to the Future a better movie.

In fact, I'm still waiting for a time travel story that would be as fun as Back to the future, and as logically consistent as Primer. Creating a story like that shouldn't be that tough. The movie Looper (2012) that's just about to hit the theaters will probably deliver in the entertainment department but is unlikely to succeed otherwise, as the whole premise heavily suggests the idea of a Self-adjusting reality.