The Tesseract
A tesseract is a four-dimensional geometric shape, also known as a hypercube. It extends the concept of a cube into an additional dimension, making it difficult to visualize since humans perceive only three dimensions. In a tesseract, each edge connects to four other edges, and it can be represented in three dimensions through projections or shadows.
In mathematics and physics, tesseracts are used to explore concepts of higher dimensions and can help in understanding complex theories, such as those in string theory. They also appear in popular culture, notably in the book "A Wrinkle in Time" by Madeleine L'Engle, where they are used as a means of travel through space and time.