The fact that our universe, like Appleworld, is curved in an unseen dimension beyond our spatial comprehension has been experimentally verified. These experiments, performed on the path of light beams, shows that starlight is bent as it moves across the universe.

Hyperspace : A Scientific Odyssey Through Parallel Universes, Time Warps, and the 10th Dimension, Chapter 1 (p. 17), Oxford University Press, Inc. 1995