Almost 100 years after A. (which we find out stands for Albert) Square's adventures that were related in
Flatland, his great-great-granddaughter, Victoria Line (Vikki), finds a copy of his book in her basement. This prompts her to invite a sphere from Spaceland to visit her, but instead she is visited by the "Space Hopper" (a character looking somewhat like the "
Space Hopper" children's toy with a gigantic grin, horns and a spherical body). The Space Hopper, more than being able to move between Flatland and Spaceland, can travel to any space in the
Mathiverse, a
set of all imaginable worlds. After showing Vikki higher dimensions, he begins showing her more modern theories, such as
fractional dimensions and dimensions with
isolated points.
Topology and
hyperbolic geometry are also discussed, as well as the Projective "Plain" (complete with
intersecting "lions") and the
quantum level. Hopper and Victoria also visit the Domain of the
Hawk King to discuss
time travel and the
theory of relativity.
How to Escape from a Black Hole This is a diagram explaining how to escape from a black hole as mentioned in the book. • You are outside the
black hole. • You have fallen into the black hole. A future version of yourself (4) appears and gives you a portable
white hole. You use the portable white hole to escape the black hole. • Another future version of yourself (6) appears and gives you a
time machine. • You go back into the black hole and give the past version of yourself (2) the portable white hole. • You use the time machine to go far enough into the future (i.e. millions of years) that the black hole has evaporated due to
Hawking radiation. • You then travel back in time and give the past version of yourself (3) the time machine. • You are now outside of the black hole. The dashed red line indicates the path of the portable white hole (clockwise). The dashed blue line indicates the path of the time machine (counterclockwise). Movement from the bottom towards the top generally indicates movement forward in time (not to scale) and vice versa. ==Real-world references==