Perhaps,when one is using a microscope, viewing single-celled organisms, he takes note of the "cell membrane" that each one has. This "outer skin" protects the cell from other cells in this flat, 2-D environment. How "protected", though, would it be, from the person viewing, who has access to the sum total of everything inside the "outer skin"?
The book Flatland deals with little sentient beings who live in such a "tabletop-like" world. Such a universe would be limited entirely to a mere length and width. All planets and stars would be circles - little dots speckled all over their universe - the surface of a giant sphere.
If their universe is the surface of a giant sphere, what is the shape of our own? A "hypersphere"? Or does no 4th spatial dimension exist? And if it does, what limits are there to what we can know about it?
The material within this section often goes into discussion as to the shape and orientation of different surfaces. However, the material is written in a way that anyone can understand - free of any bewildering terms and strange concepts.
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