This is going to be a bit lot confusing.
Because, in reality we flip between one reality and the next billions of times a second. It is actually how we experience time and motion. And so, we are very often creating reality splits for ourselves. We see two choices ahead, and we often experience both choices.
However, what i referring to by this title is a split that is a choice by humanity. You could say it is a choice of those who choose to stay in 3D and those who wish to advanced into 5D.
What does the split even look like? Can we actually see it? Can only certain people see it? And, does there actually have to be a split? Can't we just stay together?
I will try to describe this process… And i will fail badly (we don't have any good words that we share to communicate with in this area)
Imagine aliens vs no-aliens
Now, you, personally, can decide if space aliens exist in your world.
You can choose to never see, never interact with aliens. And, if you do this alone, and the rest of the world decides to have interactions with aliens, you will be seen as insane. Or, just lucky, (or unlucky.) Someone who lives under a rock and doesn't see the news.
But, if the entire human race decided to not interact with aliens, we would just never meet them. They would go left, while we go right.
Now, imagine that half of humanity decided to see them, and half decided to not. It could work if just a villiage, or a tribe decided to not see them, and they would seem to be cut off from the rest of the world. Like the mythical tribe that never has been tainted by modern humans.
But, if half decided to see them, and the other half to not, there would be too much overlap, and one side or the other would have to abandon their choice, and join the greater whole, or they could split.
There would be a world with aliens and a world without. But, most people would never notice, because they would just see their world as THE WORLD.
3D vs 5D
This may take on different effects, or different visualizations for different people.
If you are a gamer, a description would be that you see the normal 3D and also a mini-map in your mind.
If you are a trained fighter, a description would be that you see the normal 3D but you also feel/see everything around your
Another way it could manifest as is that you see the normal 3D but also have a sense of what making a choice leads to. You can see the futures you are walking into.
The thing is that the people on the bleeding edge will get these "abilities"/view-points first. And, if they try to discuss it with others, with "normal" people, they will be told they are idiots, crazy, loony, should go get checked up, check themselves into a mental hospital… Just like people who can see ghosts or spirits do today.
So, if you start seeing things, don't just blurt them out. Make sure your group is receptive AND that they are not solid-3D people. (these people may act nice to you, nodding with your story, but they will find some way to split from you. And it might be painful, or very painful. An old-good friend may even attack you, because they cannot accept 5D)
Why the split?
We, the group of people on this planet have to stay in a particularly close band of beliefs. We are working in a shared reality. There is no real world out there, we are each in an individual bubble, and the way we interact is quite complex. And their are many beliefs that build our world and interactions.
Like, one person cannot be thinking we are playing chess, and another thinking we are playing checkers. This is sorta a bad analogy, because the person playing chess couldn't see the person playing checkers, they would be on different boards (worlds). We have to keep a focus on the shared beliefs so we can stay in the same game, on the same game board. (our sub-subconscious does this, and so, we, and our subconscious, believes this is the way the world is)
So, as we move, more and more strongly towards a group that is in 5D and a group that is in 3D we will have less and less overlap, until we aren't interacting with eachother at all. And that is a split.
Of course, there will be some explanation. (every moment of now, comes complete with a past and a future) Something to describe were the other half of people went. And, quite literally, another part of you, may stay on the other side of the split.
The split happens because a group of people cannot hang with the other. If a person wants to stay in 3D, then they will be extremely combative/resistant to any change. If they won't make the jump to 5D, then they will tend to avoid 5D people (and visa versa)
At this same time, 5D people will learn more and more about their vision/sight/perception and come to accept it, and then rely on it. It will become a part of who they are.
And so, we will see a sort of self sorting. There will be people in the 5D camp, and some who cling desperately to 3D and some in the middle who will gravitate towards 5D, but some will retreat to 3D. And then, at some point the division will be too big, and we will just stop seeing the other group.
From the 5D people's perspective, the 3D people just stopped existing (probably), or the 5D people felt they shifted into another world, that they can see now because of 5D. And from the 3D people's perspective, the 5D people all died off, or left for Mars, or were taken by aliens. There will be some story that makes sense to those people.
Probably within 50 years we will pass the point where there can be people who are on the line. This is the point were there is actual split.
And those who choose to stay in 3D, it is not permanent. You are not barred from ever experiencing 5D, it is just that you will most likely have to croak in between you shifting form 3D to 5D.