The constancy of the speed of light is a fundamental principle in physics, established by Albert Einstein’s theory of special relativity. According to this theory, the speed of light in a vacuum, denoted as “c,” is an unchanging constant, approximately 299,792,458 meters per second (or about 186,282 miles per second). Special relativity posits that the speed of light is the same for all observers, regardless of their relative motion. This principle has profound implications for our understanding of space, time, and the nature of reality. The constancy of the speed of light challenges classical intuitions about the nature of time and space, leading to effects such as time dilation and length contraction at relativistic speeds. It also forms the foundation of Einstein’s famous equation, E=mc^2, which relates energy and mass. The constancy of the speed of light is a well-supported empirical fact, confirmed by numerous experiments and observations. It underpins our understanding of the laws of physics and the structure of the universe, shaping the foundations of modern physics.