On this and that
a straight line is purely a mental abstaction which in reality cannot exist in a non-euclidean (curved) universe. it will always be a minute fraction of a circle, as a line drawn on the floor is a minute curve upon the circumference of the earth.
the mind abstractly organizes to fit (make sense of) its own limited dimensional level of perception. until instruments sensitive enough to measure universal truths are created the mind can only imagine them behind the sensory illusions in which we are cradled