I was thinking around a bit. We are unable to perceive anything that is not 3D (width, length and height). Think about it, for example, we can illustrate a 2 dimensional surface, but for us, it will be impossible to literally perceive it, without the surface having at least a bit of heigt (for instance, these letters look 2D, but if they wouldn't have had a certain amount of height, they would just be invisible. another example, the ink on a paper can be seen as 2D, but has a tiny amount of atoms that make up the height). 1D, or a single point, is also impossible to perceive if it wouldn't have at least a bit of width, a bit of height and a bit of length) So the idea is that we can never perceive anything but 3D, only ways to interpret it.There are no things known and observable to us in directly in diff. dimensions. If we use that idea to go a little further, we can say that, when we think about a 2D surface (as a thought, not literally perceivable), and apply a mass to it (like Einsteins spacetimecontinuum in a 2D model) , it will bend through, thus implying an extra dimension (height, or in this case depth), 3D. So allowing our 2D universe we've created to be dynamic, it needs an extra dimension, in which the force will be observable.. In our 3D world, this would mean that the curvature of spacetime,through masses, and the perception of spacetime as a whole, is only possible through a 4th dimension.