As Mrs. Whatsit and Charles Wallace explain to Meg and Calvin, there are five dimensions. The first three can be perceived by the human senses. Meg explains that the first dimension is a "line," (length) and the second dimension is a "square" (length and width) that one can draw on a piece of paper. The third dimension is no longer flat—it adds depth to the length and width of the first two dimensions.

After that, the concept of dimension becomes more abstract. The fourth dimension is time. Charles then explains that the fifth dimension is the tesseract. By using this dimension, one can quickly travel across space.

Mrs. Whatsit and Mrs. Who illustrate that a tesseract is a wrinkle in the space-time continuum. Mrs. Who first smooths her robe flat to show that if you were very small and tried to cross the robe that way, it would be a huge, time-consuming plain to cross. However, if you wrinkle the material up, you can bring the ends very close together and quickly jump from place to place. In this tesseract, or wrinkled dimension, you can "tesser," or leap from place to place.

By using the fifth dimension, Mrs. Whatsit, Mrs. Who, and Mrs. Which can transport the children to different planets, most notably Camazotz.