Einstein's Special Theory of Relativity can also be referred to as Einstein's theory of special relativity or simply special relativity. The theory explores the relationship between space and time, and how they are perceived by observers in different states of motion. Another synonym for this theory is the special theory of relativity, which distinguishes it from the general theory of relativity. Alternate terms for the theory include the theory of invariance, the theory of the uniformity of nature's laws, and the momentum theory. Regardless of the synonym used, Einstein's Special Theory of Relativity remains a foundational scientific idea that has withstood the test of time and helped to shape our understanding of the universe.