Okay, this si the explaination my science teacher gave to the fourth dimension. Image you're a cinemascreen-creature. The cinemascreencreature only sees in 2D. When you project a cube on the screen, it sees a square. So when we place it on a ball and it starts walking straight on, it will never, ever, realize it is actually coming over the same point every time again. Because he doesn't know shapes return to the same point if you follow a straight line. The creature will never understand this third dimension.
We humans see three dimesnions, but place us in a fourth and we will never realize, because we're not capable of understanding. We did figure out that there are three dimension, but maybe the cinemascreen creature did the same for it's two dimesnions. But none of us can understand the next dimension. So, to be short: Give it up, 'cause we're not capable of finding, undertsanding or realizing this forth dimension.