This makes an interesting question to look at for my first post.
Alternate Time-lines. Tracks. Lines. Pathways. These are dangerous contradictions to comtemplate for most people if you're digging below the surface, as they provide some very conflicting moral arguments that would make people squirm and not wish to think about it.
Allow me to explain, by demostrating in either the existance or non-existance of alternate time-lines.
If there wasn't alternate time-lines, everything would be linear, which would also mean everything would be predictable, which ironically could allow for information of the future to be gleaned. It would also give rise to the moral question of 'fate'. You can't escape it as there is no alternate (since, obviously, we're discussing linear).
However, this is where the contradiction starts (I've already worked these ideas through several times already). If it IS linear, then you can predict, so you can foresee what happens and change it, which then means it's not linear... unless the changes were part of the linear process all along and it's a 'false choice'. But then you would argue what if I predicted myself predicting my prediction and knew it was linear and stopped it all from occuring?
The next contradiction lies here. If there are alternate time-lines, then prediction will be rendered impossible as any one time-line could be used, so the predictable becomes the unpredictable, thus rendering it linear again in an even further and interesting twist. I dubbed it the 'Central Nexus Theory' for an easier referrence. Basically, if you have more than one possible prediction, it proves the uncertainty remains and the predictions are worthless.
So, I thought, and I thought. What theory would allow the contradictions to be removed, but both linear and non-linear time to exist? Easy. Switch points.
Imagine time like a train track rather than like a million different tree-branches. For the most part it is linear *until* you reach a switch point, which, depending on the operator's decision (you, me, anyone), the track can either switch to another time-line, or remain on course.
Here's the twist - since all the tracks remain linear (no matter which one you choose, the track has already been laid down), you can predict what happens on every one, as in, every single possible alternative has already been mapped out. What can't be predicted is your path along these tracks. A bit of track A. A bit of track B.
And I know what you're thinking (linear track thinking, bah). If every one is already mapped out, then surely so is the path you will choose. Not true. Since every single alternate possibility has already been mapped out, the Central Nexus Theory applies - the unpredictable remains in the predictable since there are so many alternatives.
And, if every track can be predicted, so can the future, so you know where the switch points are so you can make your track changes even more unusual! Living in a track where you're about to die? Switch over to a track where you steal a car and drive to safety!