The Fourth Dimension + Beyond

PART ONE: THE 4TH DIMENSION
Imagine a line; Length - the 1st Dimension.
Imagine a square; Length and Width - the 2nd Dimension.
Imagine a cube; Length, Width & Depth - the 3rd Dimension.

Imagine the 4th Dimension like this; another cube extending off the back of the 3rd Dimensional cube. Got that? Now imagine an infinite number of cubes in such form; all connected to one another, and running in an infinite line.
What is the reasoning behind this line? If we consider the original 3rd Dimensional cube is our object of focus, then the other cubes are it, but as it appears in a different moment of time. In other words, the cube immediately next to it is the same cube, a millisecond later, and the cube on from that is the same cube another millisecond later, and so on.
This type of representation supports the theory of time travel. For travel to be possible, the place of destination must exist. In other words, for time travel to exist there has to be a time and place for the person to travel to. As such, if time travel is indeed possible in these methods, then it must be assumed that every millisecond (for lack of a better word) of the universe exists on a separate plane of existence simultaneously. This is what the line of cubes represents; a millisecond of events in the universe, beginning and ending at some unknown location.
It should also be remembered that the "line" concept would not realistically illustrate such a dimension - each cube is the same place, and as such, all the cubes and times should occupy the same area simultaneously.

PART TWO: THE 5TH DIMENSION
The 4th Dimension seems simple enough, once you grasp the basic idea behind it. Describing the 5th Dimension is much harder. The simplest (and completely incorrect) way of depicting it is to imagine a second infinite line of cubes running next to the cubes that make up the 4th Dimension. Put simply, the 5th Dimension is an alternate universe. This is a world where something as little as the placement of an atom has resulted in a completely different turn of events for the people within.
Here the first of the errors with the "Second Cube Line" arise. For one, there would not be just one of these cube lines; there would be beyond infinite! Remember, each single cube represents a millisecond of time in the universe, and when one considers that a single atom displacement results in one of these cubes results in another world, then consider how many worlds can and must exist; how many times and places an atom could be different in - A number so high that it would likely take the space of a universe to completely write it down.
With that in mind, another error comes to mind - a model of such a Dimension would be cone-shaped, not cube-shaped. All such changes would originate from one original point - the beginning of time - and then branch out from there, like the branches on a probability tree.
In addition to this, the title "5th Dimension" is a misnomer - there are multiple universes occupying the same Dimension. Whichever universe receives the title of "5th Dimension" is determined by the location of the person identifying the other places. Each universe is a "5th Dimension", in relation to the other universes, which would all contain a "4th Dimension" and exist in a "3rd Dimension" state.

PART THREE: THE 6TH DIMENSION
It would seem that by this point there would be no more room for any Dimensions - how could one go any higher than time and alternate realities, arguably covering any possible outcome for anything?
If a 6th Dimension did exist, a being inside it would be capable of seeing all the various 5th Dimensions at once, as well as every moment of time from the various 4th Dimensions. In other words, they would be omnipotent. If a God exists, it would be there that he or she would reside.

PART FOUR: TIME AND INTERDIMENSIONAL TRAVELLING
Two types of time travel are used by authors who use it as a plot device in fiction; Stable Time Loops, and Unstable Time Loops.

Type 1: Stable Time Loop:
Scenario: A person manages to go back in time. When they return to their present time, their actions in the past will not have changed anything - this is due to time travel meaning that their actions in the past would have happened before they even travelled to the past.
Example: Harry Potter And The Prisoner Of Azkaban.

Type 2: Unstable Time Loop:
Scenario: A person manages to go back in time. When they return to their present time, their actions in the past have changed some of the aspects of their present, perhaps for the better, perhaps for the worse.
Example: Back To The Future.

It's worth noting that an Unstable Time Loop does not necessarily mean that a person will wind up in a drastically different world from the one they left. The laws of probability and the Butterfly Effect itself both allow for an insane number of possibilities to occur, either good or bad, with none more or less likely to occur than the other. In popular media, it could be said that the Back To The Future Trilogy represents the best possible outcome for entering an Unstable Time Loop, whereas The Butterfly Effect represents the worst possible outcome.
Generally it is considered impossible for a story to contain both versions of a Time Loop, as the very nature of one cancels the other out. However, with this model of the universe, both are allowed for. A Stable Time Loop requires only travelling within the 4th Dimension - time, which as mentioned before will be unaffectable - whereas an Unstable Time Loop requires travel through the 5th Dimension as well as the 4th - by altering the events in their original past, a time-traveller has moved away from their original present and onto a new timeline of future events.

PART FIVE: FREE WILL AND PREDESTINATION
If the universe indeed does exist to the specifications I have described here, then this also adds another debate to the mix - that of Predestination and Free Will. They are one and the same.
Predestination is a religious concept that people's actions were already decided for them, and that they would be unable to change them in any way. Free Will, as the name suggests, is the opposite of this, a concept that people are free to make choices towards their actions, and as such alter how they would turn out.
Consider if a time-traveller visited the future, and discovered that a friend of theirs would become a King of some new country. Ignoring Time Loops, and the potential differences that might occur if he informs his friend of this outcome, his friend will arguably of his own free will become King, and yet to the time-traveller, his actions were predestined.
Predestination and Free Will are the same thing; it merely depends on whose point of view the knowledge is coming from. To a higher dimensional being, capable of seeing multiple times at once, a single person's life would be predetermined, but to the single person, their life would be unwritten, and free for them to alter. When reading a book, a person turning the pages could skip to the end, and as such know the outcome for the characters within, and yet the fact that the characters have free will throughout the entire book has not changed - the choices inside are their own.

PART SIX: CONCLUSIONS
So what does this all mean?
Does this have anything to do with the Meaning Of Life? In a way, yes, but only as a whole. Through the various universes where any number of outcomes has happened a million times over in many different ways, arguably every possible event ever imagined and every event not imagined will ultimately occur, meaning that life in a single universe has no meaning, but together as a part of a series of universes, life functions as a test of probability, and how things could work out.
What does this mean for the average person? Absolutely nothing. All this means is that there are an equal amount of worlds where wondrous things have happened to them, an equal amount of worlds where horrible things have happened to them, and an equal amount of worlds where nothing of either has happened to them. This cannot be changed, and so there is no point thinking about it or worrying about it. Que Sera Sera; What Will Be, Will Be.