Mirrors And The Fourth Dimension
Mirrors do not show us a fourth dimension, but they do show us what a fourth dimension could do to us. First, notice that some things are the same as their mirror image, but some things are not. These two shapes are similar, but they cannot be rotated to look identical, to be superimposable on each other. This is called being chiral.
A chiral shape and its mirror image are called anatomorphs. These two shapes are anatomorphs in two dimensions. No amount of two-dimensional rotations will ever make them superimposable. To do that, I'll need to smash one of them inside out, turn it into its own mirror image, or rotate it in a third, higher dimension.
If I place a sticker here and face that side away from me, notice that the mirror inverts the object, just like a rotation through a higher dimension. The side of the real object that's furthest from me becomes the side of the virtual object that's closest to me. So, what would I look like if I was rotated around a plane in a fourth spatial dimension and then brought back? I would look like that.