Linear and Alinear Time Travel

Of all the great mysteries of the universe -- the nature of god, the variations of the human mind, where keys disappear to and, of course, women -- one in particular draws my attention and hardly a day goes by without my thinking of it.

Time.

I don't know why. Passion drives our activities, but what drives passion? A need to know the past? A desire to change it? To know the future and gain a greater sense of decisiveness in the present moment?
I never think there is one answer to a single question, nor is anything ever driven by a single reason. So my love of time is probably attributed to a multitude of thoughts and desires and have condensed into a single interest.

Time.

There's another one. Repetition. Time links things together. It connects us, and yet at the same time separates us. Sometimes I feel hopelessly alone and unconnected. Huh. Humans are funny creatures. My solution to that feeling of aloneness would be to say that everyone feels alone because there is no-one exactly like them and no-one who can be exactly certain of their thought patterns or emotions, and in that we are linked to one another -- united by our sense of loneliness. Somehow, that doesn't satisfy me. My sense of reason dictates that the only person who knows me completely is myself, and so to end my feeling of loneliness I would need to encounter myself. The only versions of myself I can separate from my current state of consciousness are those who exist in another time, past or present.
So that gets me thinking of time travel, the only perceivable way in which I might meet myself. It is an enticing thought. A scientific interest, combined with an emotional revelation. Ever the cynic, I doubt I will live long enough to walk into a time machine and meet myself in the past. Much like 'serious' scientists who refuse to acknowledge the impossible and call it a 'pseudo-science' I do not entertain the possibility, merely the fantasy.
However, the fantasy will not remain a fantasy for everyone. At some point in time, science will allow time travel to happen and the fantasies of the 19th, 20th and 21st centuries will become the theories upon which primary investigations into practical time travel revolve.
So now, I sit here in the past, and I vainly call myself a temporal theorist, perhaps hoping even as I type this for a visit from the future by some time traveller other than myself. I debate the various works of fiction I have read and seen and I try to piece together a working system based on the many possibilities in existence. There are many sources to be analysed. Herbert Wells' "The Time Machine". Michael Crichton's "Timeline". The highly confusing television series, "Heroes". Various romantic takes, such as "Kate and Leopold", and "The Time Traveller's Wife". Harry Potter.
To someone who wishes to create theories about something that does not exist in this dimension, shouldn't one rely on something that does not exist? Why not? Have a look and see just one of the principles I'm investigating.
The basic principles have their foundations in scientific theory. After all, we aren't complete Neanderthals. We are, in fact, Homo Homo Sapiens, which in future times will probably be an equivalent insult.

Time is called the Fourth Dimension; sitting beside its brethren, length, width and height, the essential agents of a single state of being. Everything in existence is said to have these four properties -- even vacuums. Of course, a sensible person might point out that everything in existence also has a temperature (including vacuums) and a degree of luminescence (vacuums debatable on this one) and many other things which would split our dimensional requirements into a list too long to teach to high school students.
So for the present, reality/existence has four dimensions which define a single instant. To confuse things further the linear transformation from one instant to the next is also considered a single 'dimension'. In this sense science fiction often refers to 'parallel dimensions', which have the same temporal value as our own but bear differing aspects of length, depth and height.
These parallel dimensions hold value in the messier examples of time travel. Take for example the fictional work (some might even call it the parallel dimension) of the "Red Alert" series. It discusses the possibility of a time machine being used to kill Adolf Hitler before the holocaust in order to prevent the second world war and the subsequent tragedies involved. When the time traveller returns to the future, they find that though they have progressed along their original timeline, the three spacial values of dimension have altered to fit the adjusted ones caused by the time traveller. Without Germany as a military superpower, the Soviet Union becomes much more powerful than it would have been otherwise and is a key player in a vicious power struggle with the Allied Forces.
This is the first kind of what I term "Alinear Time Travel", because it involves crossing between two or more parallel universes. It can become extraordinarily confusing, but personally I find it as a viable theory, because it explains why our own timeline isn't poked through with wormholes leading to a future where time travel is possible.

Predictably the other theory is "Linear Time Travel", which would be a consistent timeline with an internally viable temporal discrepancy. This type of time travel is more rare, as writers need to concentrate to make sure they work out effectively. A great example would be J.K Rowling's Harry Potter and the Prisoner of Askaban, wherein the character Hermione has to muster all her wit into travelling through time without altering the preexisting reality in a visible way. It deals remarkably well with the quantum theories concerning "probability" and "possibility", and even the concept of "certainty".
First, Miss Rowling establishes the "certain" dimensions of the timeline through the use of various observations and hints about what is to come.

• Harry feels as if he is being watched.
• (cinematic) There is a rustling at the edge of the Forbidden Forest.
• Hagrid howls as an axe fall is heard.
• Harry sees someone who looks like himself cast a Patronus to banish a hoard of dementors.

From this we gain a probability -- less politely called an assumption -- of what has happened.

• Harry is breaking the rules, so he is likely to be paranoid.
• (Cinematic) The Forbidden Forest is filled with a variety of lifeforms, any of which could cause leaves to rustle.
• Buckbeak has just been executed, and Hagrid is overcome with anguish.
• By the shape of the Patronus, we are led to the hopeful assumption that James Potter has survived and has returned to save his son from having his soul eaten.

However we must admit at this point that probability is pure conjecture. It 'could' be happening. Sometimes it is even what we believe we are being led to 'know' is happening. A chapter or two later, Miss Rowling rubs our noses in the fact that we are wrong, because instead of the "probable" being confirmed to be "certain", it turns out that the "probable" is, after all, only "possible", and the "improbable" is indeed "certain".
For the improbable reveals itself as:

• Harry's paranoia was justified, as he was watching himself from the forest.
• (Cinematic) The future  Harry and Hermione caused the leaves to rustle.
• The executioner has swung his axe into a barren stump out of frustration, as Buckbeak has escaped, and Hagrid's howl is of uncontrollable happiness.
• Harry saw himself cast the Patronus.

Thus the nature of Alinear time travel is divined: the "possible" can be changed, despite the "probable", so long as the "certain" remains unaltered. This principle relies heavily upon the age old paradigm: 'if a tree falls in a forest, and no one is there to hear it, does it make a sound?', more directly phrased as "does something exist until we sense it?"

Another example of a Linear Temporal Loop is detailed below.
One day while walking through the park I witness a neatly wrapped parcel appear out of thin air and land directly in front of me. Curious and excited, I unwrap the parcel with trembling fingers to reveal a crumpled schematic. Upon investigating the schematic, I realise it is a blueprint for the construction of a simple time machine, which could easily be created by linking my microwave to a lava lamp and adjusting the speed of the turn table.
Naturally I rush home to see if it works, and swiftly build my slightly-retro time machine. For a moment I am at a loss at to what I should use it for. Then it dawns on me that I need to send the schematics back through time to the park so I will find them that morning. I wrap them up exactly as they were and send them back in the time machine to the precise time I saw them appear.
With this done, I sigh to myself and realise I need a bigger microwave.

This example shows that in Linear time travel, certain events can only occur if the future events remain constant. If, for example, I decided I was hungry while walking through the park and I would be better served by sending back a burrito I would change the past that allowed me to build the time machine, preventing me from sending anything back at all and indeed destroying the dimensional values of the instant my consciousness resided in. This would have two possible results:

• The death of my consciousness and the space time continuum as I know it.
• The manifestation of an Alinear temporal loop.

In the second and far more preferable case, three parallel dimensions exist at the same time: one in which I send back a schematic for a time machine, another in which I send back a burrito, and a third in which I am very confused but pleased by the instantaneous manifestation of a delicious Mexican snack food.
The second option also suggests a far more complicated relationship between parallel dimensions wherein by deliberately reshaping "certain" events we can construct sequences that don't rely on a single timeline of instants, but on several crossing timelines' instants.
The general rule is:

• Time travel affecting possible events in order to bring about a different one than is generally considered probable (without time travel) creates a Linear temporal loop.
• Time travel which directly alters certain spacial dimensions will result in an Alinear temporal loop.

Which is really what Miss Rowling illustrated in her book. Yet, for some reason, people think that the possibility of colliding several parallel dimensions in an Alinear temporal loop is dangerous... More on that later.