Since ancient times, philosophy has grappled with fundamental questions: Why does our space have three dimensions, while time has only one? Why are all objects around us extended in three spatial dimensions and only one temporal dimension? The advent of Einstein’s theory of relativity introduced a new challenge—one that profoundly impacts our entire understanding of the universe: why is spacetime four-dimensional? The problem of space’s three-dimensionality dates back to the early days of science itself. Despite over two centuries of scientific progress, the mystery of why our universe has three spatial dimensions and one time dimension remains unsolved. This book explores the main approaches to understanding this puzzle through the lens of philosophy and natural science. It reveals how, over time, it has become clear that only theoretical physics can provide a potential answer. The book also examines some promising perspectives from modern physics on solving this complex problem. Additionally, it raises the question of whether the universal property of three-dimensional space and one-dimensional time can be explained, and whether the data of contemporary science and principles of dialectical materialism allow us to imagine the existence of a real universe with an unusual topology—particularly, with a different number of dimensions. Written as an engaging popular science essay, this book is aimed at readers interested in the philosophical issues at the heart of modern natural science.