The third is the dimension in which we feel at home. Our space is three-dimensional. And this time, again, we must add a new line in space. To length and width, we add a third dimension which is height.
Therefore, a three-dimensional body has length, width, and height. Like every human being, every house, the Earth, or any observable body in the Universe. In the Cosmos with which we interact, objects are three-dimensional, and we move in a space that is also three-dimensional. We only have to look around to understand this dimension.
Imagining three dimensions is extremely simple since we are used to a three-dimensional environment. Length, width, and height. But you can see another way to define the third dimension. Recall the flat two-dimensional universe, imagining that it is a huge cardboard, which we fold in such a way that some points of the cardboard are in contact with other points of the cardboard. A two-dimensional being inhabiting that folded two-dimensional universe would not be able to perceive those folds. But in certain places, it could pass from one point of its universe to another very far away (for it), in an instant of time, since those two points touch each other, because the cardboard is folded. Let us now return to the one-dimensional beings. For them, the second dimension would be a bifurcation in their linear universe, so that they could access another linear universe. But if that «two-dimensional multiverse» folds into a third dimension, one-dimensional beings could not only go to other one-dimensional universes, but to other points in their own universe. Moreover, they could move to another linear universe without the need to use the «bifurcation» where their universe is cut off from the other.
To recapitulate: one dimension means that I can join two points with a line. A second dimension means that my line bifurcates at certain points. A third dimension means that I can fold those lines.
I invite everyone to read Matias’ post with the topic of the day.
Finally, I encourage everyone to reflect on the concept of the day. No one else but us can re-signify our own being