Let's just set the premise first. Imagine yourself in two different worlds - one, where the world has only two dimensions, and second, where you'll find yourself in a parallel universe. Keep these two worlds in mind as we start.
A. You are a black square on a white paper on Flatland.Namaskar. Welcome to Flatland. Everyone here lives in two dimension. You are as free as a bird here but only in two dimensions. The third dimension doesn't exist, which means you can't even go up or down here. Enjoy!
B. The other sideNow on the other side of the paper, there is a parallel universe that hosts Flatlanders like you. So can you go over to the other side and greet your neighbours? But how will you? You can't cut through the piece of paper. Neither can you dig through because the third dimension doesn't exist. However, that doesn't mean there aren't things that are 3D. Only you aren't 3D.
But there is a way.
The Mobius strip. Look at the image above closely. If an ant were to crawl along the length, it would return to its starting point after having travelled through the entire length.
But can Flatland be twisted like that? Doesn't that mean Flatland is 3D? The Mobius Strip is 3D, but like those ants, the Flatlanders are limited to the two dimensions of the paper. So, it's possible.
Okay, time to come out of fantasy land now. Things are about to get pretty interesting here on.
If you look at it, we are quite similar to the population of Flatland. Just like them, we are free to move about in 3 dimensions, but can travel in the 4th dimension. 4th dimension to us is time. We can't alter time. Yet.
Now think of a Mobius Strip made up of our universe in 3 dimensions which is twisted. That actually gives us access to a parallel universe, i.e the other side of our 3D universe. A place where you might meet a version of you that's living the life that you have always dreamed of.
Growing jealous, you decide to replace him. Things start getting complicated from here, won't they? The world as you know it would change. Like we changed that ant's reality on the Mobius strip, do you think there is something, or someone with access to the 4th dimension creating twists in our lives? It doesn't feel so over-the-top now, does it?
2. Hubble Bubble experiment.